Details of a Researcher - Einaga, Yasuaki

Papers - Einaga, Yasuaki

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Fabrication of three-dimensional boron-doped diamond electrodes on SiC scaffolds

Otake A., Diaz-Herrezuelo I., Uchiyama K., Fiorani A., Belmonte M., Einaga Y.

Diamond and Related Materials (Diamond and Related Materials) 146 2024.06

ISSN 09259635

Three-dimensional (3D) architected electrode materials are expected to exhibit advantageous properties such as enlarged surface area, increased mass transfer, enhanced adsorption and more active sites exposed. In this paper, boron-doped diamond (BDD) electrodes on 3D printed patterned silicon carbide (SiC) scaffolds have been fabricated using chemical vapor deposition (CVD). The stabilization of the plasma sphere by using clamshell type CVD reactor, introducing the outer protecting plate, the optimization of CVD parameters, and the design of 3D-SiC scaffolds improved the sp3/sp2 ratio, uniformity and growth rate of BDD. 3D-BDD electrodes exhibit enough electrical conductivity for electrochemical applications. The preliminary test for electrochemical carbon dioxide reduction (CO2R) has showed the potential advantages of this type of 3D structured BDD electrodes.

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Fabrication of polycrystalline phosphorus-doped diamond electrodes from red phosphorus

Moriguchi T., Tomisaki M., Sato S., Nakamura J., Yamada H., Einaga Y.

Physical Chemistry Chemical Physics (Physical Chemistry Chemical Physics) 26 ( 20 ) 14825 - 14831 2024.05

ISSN 14639076

Polycrystalline phosphorus-doped diamond was fabricated by the quartz-tube-type microwave plasma-assisted chemical vapor deposition method. Significantly, red phosphorus was used as a source of phosphorous, instead of PH3. Phosphorus-doped diamond electrodes with hydrogen-terminated and oxygen-terminated surfaces were investigated for the redox reactions of K3[Fe(CN)6] and [Ru(NH3)6]Cl3. The carrier concentration was estimated as 2.1-5.3 × 1018 cm−3 from electrochemical impedance measurements. Polycrystalline phosphorus-doped diamond shows great promise as chemical electrode materials.

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Green Synthesis of Ceria Nanoparticles from Cassava Tubers for Electrochemical Aptasensor Detection of SARS-CoV-2 on a Screen-Printed Carbon Electrode

Zakiyyah S.N., Irkham N., Einaga Y., Gultom N.S., Fauzia R.P., Kadja G.T.M., Gaffar S., Ozsoz M., Hartati Y.W.

ACS Applied Bio Materials (ACS Applied Bio Materials) 7 ( 4 ) 2488 - 2498 2024.04

Green synthesis approaches for making nanosized ceria using starch from cassava as template molecules to control the particle size are reported. The results of the green synthesis of ceria with an optimum calcination temperature of 800 °C shows a size distribution of each particle of less than 30 nm with an average size of 9.68 nm, while the ratio of Ce3+ to Ce4+ was 25.6%. The green-synthesized nanoceria are applied to increase the sensitivity and attach biomolecules to the electrode surface of the electrochemical aptasensor system for coronavirus disease (COVID-19). The response of the aptasensor to the receptor binding domain of the virus was determined with the potassium ferricyanide redox system. The screen-printed carbon electrode that has been modified with green-synthesized nanoceria shows 1.43 times higher conductivity than the bare electrode, while those modified with commercial ceria increase only 1.18 times. Using an optimized parameter for preparing the aptasensors, the detection and quantification limits were 1.94 and 5.87 ng·mL-1, and the accuracy and precision values were 98.5 and 89.1%. These results show that green-synthesized ceria could be a promising approach for fabricating an electrochemical aptasensor.

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Modification of boron-doped diamond electrode with polyaniline and gold particles to enhance the electrochemiluminescence of luminol for the detection of reactive oxygen species (hydrogen peroxide and hypochlorite)

Rahmawati I., Fiorani A., Sanjaya A.R., Irkham , Du J., Saepudin E., Einaga Y., Ivandini T.A.

Diamond and Related Materials (Diamond and Related Materials) 144 2024.04

ISSN 09259635

A luminol electrochemiluminescence (ECL)-based sensor for reactive oxygen species (ROS), including H2O2 and hypochlorite was developed using gold particles-modified on polyaniline‑boron doped diamond electrode (Au-PANI/BDD). The gold particles were incorporated onto the surface of boron-doped diamond (BDD) electrode to enhance the electrochemiluminescence of luminol, while the polyaniline was used to provide better attachment of the gold particles on the surface of BDD electrode. The uniform distribution of gold particles on the PANI/BDD surface was verified through FE-SEM EDX analysis with an approximately weight percentage of 45.6 % (w/w). The modified electrode exhibited a remarkable five-fold increase in ECL intensity compared to the unmodified BDD, resulting in higher sensitivity. Furthermore, the sensor's performance was successfully demonstrated for H2O2 concentrations ranged linearly from 1 to 100 μM (R2 ≥ 0.99) with a low detection limit of 0.81 μM, and for hypochlorite concentrations from 1 to 20 μM (R2 ≥ 0.99) with a detection limit as low as 0.51 μM. Additionally, excellent repeatability and stability of the signals was also observed over 7 days. Furthermore, successful application in detecting H2O2 and hypochlorite in real sample highlights its promising potential as an ROS sensor.

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Sluggish Electron Transfer of Oxygen-Terminated Moderately Boron-Doped Diamond Electrode Induced by Large Interfacial Capacitance between a Diamond and Silicon Interface

Otake A., Nishida T., Ohmagari S., Einaga Y.

JACS Au (JACS Au) 4 ( 3 ) 1184 - 1193 2024.03

Boron-doped diamond (BDD) has tremendous potential for use as an electrode material with outstanding characteristics. The substrate material of BDD can affect the electrochemical properties of BDD electrodes due to the different junction structures of BDD and the substrate materials. However, the BDD/substrate interfacial properties have not been clarified. In this study, the electrochemical behavior of BDD electrodes with different boron-doping levels (0.1% and 1.0% B/C ratios) synthesized on Si, W, Nb, and Mo substrates was investigated. Potential band diagrams of the BDD/substrate interface were proposed to explain different junction structures and electrochemical behaviors. Oxygen-terminated BDD with moderate boron-doping levels exhibited sluggish electron transfer induced by the large capacitance generated at the BDD/Si interface. These findings provide a fundamental understanding of diamond electrochemistry and insight into the selection of suitable substrate materials for practical applications of BDD electrodes.

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Designing Molecularly Imprinted Polymer-Modified Boron-Doped Diamond Electrodes for Highly Selective Electrochemical Drug Sensors

Ishii K., Ogata G., Yamamoto T., Sun S., Shiigi H., Einaga Y.

ACS Sensors (ACS Sensors) 9 ( 3 ) 1611 - 1619 2024.03

Drug detection in biological solutions is essential in studying the pharmacokinetics of the body. Electrochemical detection is an accurate and rapid method, but measuring multiple drugs that react at similar potentials is challenging. Herein, we developed an electrochemical sensor using a boron-doped diamond (BDD) electrode modified with a molecularly imprinted polymer (MIP) to provide specificity in drug sensing. The MIP is a polymer material designed to recognize and capture template molecules, enabling the selective detection of target molecules. In this study, we selected the anticancer drug doxorubicin (DOX) as the template molecule. In the electrochemical measurements using an unmodified BDD, the DOX reduction was observed at approximately −0.5 V (vs Ag/AgCl). Other drugs, i.e., mitomycin C or clonazepam (CZP), also underwent a reduction reaction at a similar potential to that of DOX, when using the unmodified BDD, which rendered the accurate quantification of DOX in a mixture challenging. Similar measurements conducted in PBS using the MIP-BDD only resulted in a DOX reduction current, with no reduction reaction observed in the presence of mitomycin C and CZP. These results suggest that the MIP, whose template molecule is DOX, inhibits the reduction of other drugs on the electrode surface. Selective DOX measurement using the MIP-BDD was also possible in human plasma, and the respective limits of detection of DOX in PBS and human plasma were 32.10 and 16.61 nM. The MIP-BDD was durable for use in six repeated measurements, and MIP-BDD may be applicable as an electrochemical sensor for application in therapeutic drug monitoring.

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Impact of gate electrode on free chlorine sensing performance in solution-gated graphene field-effect transistors

Sugawara M., Watanabe T., Einaga Y., Koh S.

RSC Advances (RSC Advances) 14 ( 11 ) 7867 - 7876 2024.03

Free chlorine is widely used to disinfect water used for drinking and food processing. This requires highly sensitive, simple, and capable continuous-measurement sensors to enable the concentration of free chlorine in water to be monitored and controlled. Free chlorine sensors based on solution-gated graphene field-effect transistors (GFETs) are a suitable platform for highly sensitive and continuous measurements. However, their sensing mechanisms require further elucidation to improve their performance. In this study, we focused on the gate electrode and investigated its influence on the sensing performance. Using the free chlorine sensor based on the solution-gate GFET, we showed that the Dirac point voltage in the transfer curve changed significantly as the free chlorine concentration changed, and the electric double-layer capacitance of the gate electrode decreased. Furthermore, we demonstrated that a solution-gated GFET using graphene or boron-doped diamond as the gate electrode could be used to detect changes in the free chlorine concentration in the concentration range of tap water. The sensing performance in the low concentration range benefits from the wide potential window of carbon-based electrodes, which do not have electrochemically active sites. Using these carbon-based materials as gate electrodes, GFETs have the potential to be used as durable sensors that are resistant to surface fouling and oxidation.

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Real-Time Measurement of Antiglaucoma Drugs in Porcine Eyes Using Boron-Doped Diamond Microelectrodes

Ogata G., Yoneda M., Ogawa R., Hanawa A., Asai K., Yamagishi R., Honjo M., Aihara M., Einaga Y.

ACS Sensors (ACS Sensors) 9 ( 2 ) 781 - 788 2024.02

The primary treatment for glaucoma, the most common cause of intermediate vision impairment, involves administering ocular hypotensive drugs in the form of topical eye drops. Observing real-time changes in the drugs that pass through the cornea and reach the anterior chamber of the eye is crucial for improving and developing safe, reliable, and effective medical treatments. Traditional methods for measuring temporal changes in drug concentrations in the aqueous humor employ separation analyzers such as LC-MS/MS. However, this technique requires multiple measurements on the eyes of various test subjects to track changes over time with a high temporal resolution. To address this issue, we have developed a measurement method that employs boron-doped diamond (BDD) microelectrodes to monitor real-time drug concentrations in the anterior chamber of the eye. First, we confirmed the electrochemical reactivity of 13 antiglaucoma drugs in a phosphate buffer solution with a pH of 7.4. Next, we optimized the method for continuous measurement of timolol maleate (TIM), a sympathetic beta-receptor antagonist, and generated calibration curves for each BDD microelectrode using aqueous humor collected from enucleated porcine eyes. We successfully demonstrated the continuous ex vivo monitoring of TIM concentrations in the anterior chambers of these enucleated porcine eyes. The results indicate that changes in intracameral TIM concentrations can be monitored through electrochemical measurements using BDD microelectrodes. This technique holds promise for future advancements in optimizing glaucoma treatment and drug administration strategies.

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Hydroxyapatite-Gold Modified Screen-Printed Carbon Electrode for Selective SARS-CoV‑2 Antibody Immunosensor

Syafira R.S., Devi M.J., Gaffar S., Irkham , Kurnia I., Arnafia W., Einaga Y., Syakir N., Noviyanti A.R., Hartati Y.W.

ACS Applied Bio Materials (ACS Applied Bio Materials) 7 ( 2 ) 950 - 960 2024.02

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), or coronavirus disease 2019 (COVID-19), is still spreading worldwide; therefore, the need for rapid and accurate detection methods remains relevant to maintain the spread of this infectious disease. Electrochemical immunosensors are an alternative method for the rapid detection of the SARS-CoV-2 virus. Herein, we report the development of a screen-printed carbon electrode immunosensor using a hydroxyapatite-gold nanocomposite (SPCE/HA-Au) directly spray-coated with the immobilization receptor binding domain (RBD) Spike to increase the conductivity and surface electrode area. The HA-Au composite synthesis was optimized using the Box−Behnken method, and the resulting composite was characterized by UV−vis spectrophotometry, TEM-EDX, and XRD analysis. The specific interaction of RBD Spike with immunoglobulin G (IgG) antibodies was evaluated by differential pulse voltammetry and electrochemical impedance spectroscopy methods in a [Fe(CN)6]4−/3− solution redox system. The IgG was detected with a detection limit of 0.0561 pg mL−1, and the immunosensor had selectivity and stability of 103−122% and was stable until week 7 with the influence of storage conditions. Also, the immunosensor was tested using real samples from human serum, where the results were confirmed using the chemiluminescent microparticle immunoassay (CMIA) method and showed satisfactory results. Therefore, the developed electrochemical immunosensor can rapidly and accurately detect SARS-CoV-2 antibodies.

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Anode Reaction Control for a Single-Compartment Electrochemical CO<inf>2</inf> Reduction Reactor with a Surface-Activated Diamond Cathode

Otake A., Asai K., Einaga Y.

Chemistry - A European Journal (Chemistry - A European Journal) 30 ( 9 ) 2024.02

ISSN 09476539

The electrochemical reaction of carbon dioxide (CO2) in aqueous electrolyte solutions is attracting increasing attention for sustainable chemical production. Boron-doped diamond (BDD) electrodes have been previously shown to be very effective for the stable electrochemical production of formic acid from CO2. Typically, the electrochemical production of formic acid by CO2 reduction (CO2R) reaction is performed with a dual-compartment flow reactor equipped with a membrane separator. The problems caused by the membrane separator, such as scaling-up, complicated operational control and materials costs can be solved using a membrane free single-compartment reactor. Here we demonstrate anode reaction control for a single-compartment CO2R flow reactor using a surface-activated BDD cathode and achieve a Faradaic efficiency for formic acid production of over 70 %.

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Electrochemical CO<inf>2</inf> reduction properties of boron-doped diamond powder

Miyake Y., Kondo T., Otake A., Einaga Y., Tojo T., Yuasa M.

Diamond and Related Materials (Diamond and Related Materials) 142 2024.02

ISSN 09259635

The electrochemical CO2 reduction reaction (CO2RR) properties of boron-doped diamond powder (BDDP) were investigated. A BDDP-painted electrode was prepared by casting BDDP ink on the surface of a BDD thin-film electrode as a current collector. The CO2RR properties of the BDDP-painted electrode were compared to those of conventional BDD thin-film electrodes, which were prepared directly on a conductive silicon wafer substrate by the microwave plasma-assisted chemical vapor deposition method. The result of the electrolysis at −1.8 V vs. Ag/AgCl in 0.5 M KCl catholyte showed that the BDDP-painted electrode was superior to the BDD thin-film electrode because it produced a large amount of products (formic acid and carbon monoxide) at a low overpotential. The highest performance of the CO2RR in the BDDP-painted electrode was achieved with the BDDP with high boron doping and high sp2 carbon content. We considered that structural defects, boron doping level, and sp2 carbon content influenced the reactivity for CO2 reduction. Therefore, the BDDP-painted electrodes should be useful not only for the production of a large-size electrode but also for efficient CO2RR.

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Cu, Fe, N-doped Carbon Nanotubes Prepared through Silica Coating for Selective Oxygen Reduction to Water in Acidic Media

Kato M., Abe D., Xie S., Sato S., Fujibayashi N., Matsumoto K., Onoda A., Hayashi T., Mitsui T., Fujiwara K., Yamamoto T., Einaga Y., Tadgell C.A., Kato Y., Asakura K., Yagi I.

ChemCatChem (ChemCatChem) 2024

ISSN 18673880

We report Cu, Fe, N-doped carbon nanotubes, (Cu,Fe)−N−CNT, as electrocatalysts for the oxygen reduction reaction (ORR) in acidic media. (Cu,Fe)−N−CNT was prepared using a silica coating method in pyrolysis to minimize the formation of carbon-coated metal oxide or carbide nanoparticles, which are known to be inactive for the H2O2 reduction. (Cu,Fe)−N−CNT shows a turnover frequency of 0.66 e− site−1 s−1 at +0.8 V vs. RHE and H2O2 yields of <1 % for the ORR with a utilization factor of active sites of 82 %. Kinetic analysis reveals that 4e− transfer rates for (Cu,Fe)−N−CNT are higher than those of a monometallic counterpart of Fe−N−CNT. In situ X-ray absorption spectroscopy enables us to determine redox potentials: E°’(FeIII/FeII)=0.65 V vs. RHE and E°’(CuII/CuI)=0.45 V for (Cu,Fe)−N−CNT, and E°’(FeIII/FeII)=0.65 V for Fe−N−CNT. These results indicate that bimetallic doping into carbon nanotubes gives the effect on kinetic parameters but not on thermodynamic ones. In other words, there is no direct electronic interactions between the Cu and Fe active sites for (Cu,Fe)-N-CNT because such interactions should modulate their redox potentials.

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Measuring the Permittivity of Liposome and Yeast Using a 3D-printed Electrode-replaceable Measuring Cell

Kageyama Y., Sueoka H., Kimura A., Sato M., Ito A., Horie T., Ogata G., Einaga Y., Suzuki H., Murakami S.

Advanced Biomedical Engineering (Advanced Biomedical Engineering) 13 90 - 99 2024

The lipid bilayer membrane of microorganisms exhibits capacitance that can be used to assess the proliferation, reduction, or transformation of these microorganisms by evaluating the permittivity of their lipid bilay-er membrane. Traditionally, the effects of pharmacological substances on viruses have been measured indirectly by observing cytopathic effects on cultured cells. Nevertheless, the novel approach that depends on permittivity is antic-ipated to provide an innovative assay for preliminary screening of potential drugs against microorganisms. In an ef-fort to quantify directly the pharmacological effects of compounds on microorganisms, we devised a method that avoids the indirect pharmacological effects on cultured cells. Instead, this method measures the direct effect by as-sessing the permittivity induced by the lipid bilayer membrane itself. To validate the effectiveness of our approach, and to demonstrate the feasibility of permittivity measurements in microorganisms, we designed an electrode-re-placeable measuring cell using 3D printing technology. Using this measuring cell, we measured permittivity of egg phosphatidylcholine liposomes and yeast cells, both of which exhibit lipid bilayers and are suitable for experimental purposes. We measured the permittivity of a KCl solution, as well as suspension of liposomes or yeast cells in KCl solution. We observed an increase in permittivity within a frequency range of 104–108 Hz, which can be ascribed to the lipid bilayers of the liposomes and yeast cells. Following lysis of liposomes by adding Triton-X 100, we observed a reduction in the enhanced permittivity. Furthermore, when the yeast cell count was reduced by dilution, there was a corresponding decrease in the enhanced permittivity. A decrease in permittivity was also noted in a suspension of yeast cells in KCl solution following heat and enzyme treatments. These results suggest that the permittivity of lipid bilayer membrane can be measured and harnessed to estimate the concentration of microorganisms in a solution. Consequently, we anticipate that this method will be developed as a pioneering assay for early drug screening, given its capacity to evaluate the pharmacological effects of compounds on viruses, without the necessity for cultured cells.

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Effect of the Substrate Materials in the Fabrication of an Electrode Based on Mixed Nickel-Iron Oxide Electrocatalyst

Tsuji Y., Fiorani A., Einaga Y.

Advanced Sustainable Systems (Advanced Sustainable Systems) 2024

The effect of different substrate materials in the fabrication of an electrode intended for use in the water oxidation reaction is investigated. The electrocatalyst is nickel-iron oxide (NiFeOx) which is deposited by chronoamperometry on nickel, iron, titanium, and stainless steel substrates. The process of electrodeposition is optimized to achieve the lowest overpotential for the water oxidation reaction. The four electrodes are characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and glow-discharge optical emission spectroscopy (GDOES) to describe the effect of the substrate on the nature of the electrocatalyst layer. Electrochemical tests in 1 m NaOH are applied on the four electrodes to assess the stability and the retention of the electrocatalytic properties of the whole electrode. All electrodes show similar overpotential of ≈0.3 V at 10 mA cm−2 implying that the substrate do not affect the electrocatalytic activity of the NiFeOx. After use, the overpotential increases in a range of 30–50 mV for nickel, iron, and titanium substrates, while stainless steel retains the lowest overpotential with an increase of 10 mV. This limited variation can be the effect of smaller NiFeOx nanoparticles compared to other substrates. XPS analysis reveals that after galvanostatic electrolysis, the oxidation state of Fe shifts slightly from Fe(II) to Fe(III), likely Fe3O4 and Fe2O3, while NiO/Ni2O3 change partially to Ni(OH)2.

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Electrochemical Diagnosis of Urinary Tract Infection Using Boron-Doped Diamond Electrodes

Zhang Z., Ogata G., Asai K., Yamamoto T., Einaga Y.

ACS Sensors (ACS Sensors) 8 ( 11 ) 4245 - 4252 2023.11

Efficient detection of sodium nitrite in human urine could be used to diagnose urinary tract infections rapidly. Here, we demonstrate a fast and novel method for the selective detection of sodium nitrite in different human urine samples using electrolysis with a bare boron-doped diamond electrode. The measurement is performed without adding any other species, such as enzymes, and uses a simple electrochemical approach with an oxidation step followed by reduction. In the present study, we pay attention to the reduction potential range for the measurement, which is substantially different from many previous literature reports that focus on the oxidation reaction. The determination of added sodium nitrite based on cyclic voltammetry or differential pulse voltammetry is employed for two pooled urine samples and three individual urine matrices. From this, the linear response ranges for sodium nitrite detection are 0.5-10 mg/L (7.2-140 μmol/L) and 10-400 mg/L (140-5800 μmol/L). The results from these urine samples convert well to the calibration curve, with a limit of detection established as 0.82 mg/L (R2 = 0.9914), which is clinically relevant.

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Molybdenum oxide electrodeposition on boron-doped diamond: Investigation of valence state and application in electrochemical nitrogen reduction to ammonia

Kuramochi S., Fiorani A., Einaga Y.

Diamond and Related Materials (Diamond and Related Materials) 139 2023.11

ISSN 09259635

In this study, molybdenum-modified boron-doped diamond (MoBDD) was prepared by electrodeposition from a molybdate precursor, and the molybdenum oxide valence state was investigated by XPS analysis. The molybdenum oxide was used as an electrocatalyst in electrochemical nitrogen reduction for ammonia synthesis at room temperature and atmospheric pressure. MoBDD could produce ammonia at 1.26 nmol h−1 cm−2 with a faradaic efficiency of 9.15 % which was higher than a pure Mo plate set as a comparison. The XRD spectroscopy analysis suggests that high state Mo oxides are responsible for the electrocatalytic activity.

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Surface morphology-assisted electrochemical conversion of carbon dioxide to formic acid via nanocrystalline boron-doped diamond electrodes

Ashcheulov P., Otake A., Akai K., Taylor A., Klimša L., Hubík P., More-Chevalier J., Einaga Y.

Chemical Engineering Journal (Chemical Engineering Journal) 473 2023.10

ISSN 13858947

Due to its unmatched corrosion stability and overall versatility, boron-doped diamond (BDD) has superb potential as an electrode material for the production of valuable chemicals via electrochemical reduction of carbon dioxide (CO2). To advance its practical application, it is necessary to explore ways to achieve cost-effective fabrication of BDD electrodes, which can enable significant selectivity for product formation during CO2 electroreduction. Here, BDD electrodes of nanocrystalline form were fabricated employing two distinct chemical vapor deposition (CVD) techniques, which allow for substantial upscaling of electrode dimensions to match industrial/wafer-size standards. Thin (<400 nm) nanocrystalline BDD layers were fabricated at various synthesis temperatures to investigate its effect on the electrical, structural, and electrochemical characteristics. Furthermore, modification of the BDD layer crystallinity and morphology has been performed to significantly alter the overall electrode structure and sp3/sp2-carbon phase-composition. Finally, when employed as cathodes in electrochemical CO2 reduction, nanocrystalline BDD electrodes of modified structure demonstrated enhanced values of faradaic efficiency (FE) towards production of formic acid (HCOOH), surpassing FEHCOOH values observed for microcrystalline form of BDD cathodes. Reported findings present a basis for further development of BDD cathodes, including their design, structure, and composition, which leverages the advantages of scalable and cost-effective synthesis of BDD electrodes.

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Morphology modulation on boron-doped diamond electrodes and its effect on boosting the conversion of CO<inf>2</inf>-to-CO

Peng Z., Fiorani A., Tomisaki M., Nishide Y., Hagiwara M., Fujihara S., Einaga Y.

Diamond and Related Materials (Diamond and Related Materials) 138 2023.10

ISSN 09259635

Boron-doped diamond (BDD) electrodes have achieved excellent selectivity and switchable product formation for electrochemical CO2 reduction reaction (eCO2RR), although the current should be improved. Surface morphology modulation is a promising approach for improving it by exposing a larger electroactive area. Herein, we fabricated a porous 1 % BDD film (p-BDD) and a rough-surfaced 1 % BDD film (r-BDD) by modifying the surface of a flat 1 % BDD film (f-BDD). Fundamental electrochemical properties, including potential window, differential capacitance, and active area were examined, followed by eCO2RR activity evaluation. The synthetic r-BDD electrode enabled approximately 1.7-fold increases in current density and yield rate (17.6 μmol h−1) toward CO production compared to f-BDD (10.3 μmol h−1). This improvement in eCO2RR is ascribed to the larger electroactive area with a comparable kinetic performance, in comparison to f-BDD. On the other hand, p-BDD possesses the largest real area, but showed the lowest activity for eCO2RR (1.2 μmol h−1 for CO), which could result from hindered diffusion of CO2 inside the pores. X-rays photoelectron spectroscopy and electrochemical impedance spectroscopy were employed to disentangle the morphological structure effect from the chemical reactivity of the electrode surface.

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Urine protein quantification in human urine on boron-doped diamond electrodes based on the electrochemical reaction of Coomassie brilliant blue

Aoki H., Miyazaki R., Ohama M., Murata M., Asai K., Ogata G., Einaga Y.

Analyst (Analyst) 148 ( 18 ) 4396 - 4405 2023.08

ISSN 00032654

Urinalysis is attracting interest in personal healthcare management as part of a general move to improve quality of life. Urine contains various metabolites and the protein level in urine is an indicator of kidney function. In this study, a novel electrochemical sensing system based on boron-doped diamond (BDD) electrodes was developed for the detection of protein concentrations in human urine. BDD electrodes have the advantages of a wide electrochemical potential window and low non-specific adsorption, making them ideal for simple, rapid, and compact devices for home detection of bio-relevant substances. Coomassie brilliant blue (CBB), a dye that selectively and strongly binds to urine proteins, was found to be a redox-active indicator to show a decrease in its redox currents in relation to the concentration of protein in urine samples. Our detailed studies of BDD electrodes showed their limit of detection to be 2.57 μg mL−1 and that they have a linear response that ranges from 0 to 400 μg mL−1 in urine samples. We also investigated the detection of urine protein in different urine samples. Our results agreed with those obtained using conventional colorimetric analysis. We believe this to be the first study of electrochemical detection of urine protein in urine samples on BDD electrodes, which is of great significance to be able to obtain results with electrical signals rapidly compared to conventional colorimetric analysis. This CBB-BDD technique has the potential to assist healthcare management in the form of a rapid daily diagnostic test to judge whether a more detailed examination is needed.

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Electrochemical reduction of carbon dioxide to acetic acid on a Cu-Au modified boron-doped diamond electrode with a flow-cell system

Saprudin M.H., Jiwanti P.K., Saprudin D., Sanjaya A.R., Putri Y.M.T.A., Einaga Y., Ivandini T.A.

RSC Advances (RSC Advances) 13 ( 32 ) 22061 - 22069 2023.07

Boron-doped diamond (BDD) was modified with copper and gold particles by using an electrodeposition technique to improve its catalytic effect on CO2 reduction in a flow system. The system was optimized based on the production of formic acid by the electroreduction process. At the optimum applied potential of −1.0 V (vs. Ag/AgCl) and flow rate of 50 mL min−1, the copper-gold-modified BDD produced formic acid at the highest rate of 4.88 mol m−2 s−1 and a concentration of 15.93 ppm, while acetic acid was produced with a rate of 0.11 mol m−2 s−1 and a concentration of 0.47 ppm. An advantage of the flow system using the modified BDD was that it was found to accelerate the production rate of acetic acid as well as to decrease the reduction potential of CO2. Furthermore, better stability of the metal particles was observed when using mixed copper-gold modification on the BDD surface than single modification by either metal. The results indicated that a flow system is suitable to be employed for electroreduction of CO2 using the bimetal-modified BDD electrodes, especially with copper and gold as the modifying particles.

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Electrochemical investigation of hydroxyapatite-lanthanum strontium cobalt ferrite composites (HA-LSCF) for SARS-CoV-2 aptasensors

Hartati Y.W., Devi M.J., Irkham N., Zulqaidah S., Noviyanti A.R., Rochani S., Topkaya S.N., Einaga Y.

RSC Advances (RSC Advances) 13 ( 29 ) 20209 - 20216 2023.07

The hydroxyapatite-lanthanum strontium cobalt ferrite (HA-LSCF) composite showed a good response on a screen-printed carbon electrode (SPCE) electrochemical aptasensor to detect SARS-CoV-2. SPCE/HA-LSCF with a thiolated aptamer has a strong affinity for the SARS-CoV-2 spike RBD protein. This occurs due to the binding of -SH to the HA-positive region. In the presence of LSCF, which is conductive, an increase in electron transfer from the redox system [Fe(CN)6]3−/4− occurs. The interaction of the aptamer with the RBD protein can be observed based on the decrease in the electron transfer process. As a result, the developed biosensor is highly sensitive to the SARS-CoV-2 spike RBD protein with a linear range of 0.125 to 2.0 ng mL−1, a detection limit of 0.012 ng mL−1, and a quantification limit of 0.040 ng mL−1. The analytical application of the aptasensor demonstrates its feasibility in the analysis of saliva or swab samples.

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Boron- and Nitrogen-Codoped Diamond Electrodes for the Improved Reactivity of Electrochemical CO<inf>2</inf> Reduction Reaction

Miyake Y., Kondo T., Otake A., Einaga Y., Tojo T., Yuasa M.

ACS Sustainable Chemistry and Engineering (ACS Sustainable Chemistry and Engineering) 11 ( 23 ) 8495 - 8502 2023.06

We investigated the electrochemical CO2 reduction reaction (CO2RR) properties of boron- and nitrogen-codoped diamond (BNDD) electrodes. The BNDD electrodes exhibited higher CO2RR performance than boron-doped diamond (BDD) electrodes, indicating that the nitrogen doping can promote CO2RR reactivity. In particular, the faradaic efficiencies of the CO2RR products, obtained at a relatively low negative potential (−2.0 V vs Ag/AgCl) in this study, were significantly higher using BNDD electrodes with high nitrogen-doping levels. At this potential, it should be difficult to generate CO2•- as an initial intermediate of CO2RR; therefore, nitrogen doping promoted the generation of the intermediate through another reaction pathway. Linear sweep voltammetry revealed that nitrogen doping could promote the generation of adsorbed hydrogen atoms on the electrode surface by proton reduction. Thus, we concluded that nitrogen doping promoted the initial step of CO2RR through the adsorption of hydrogen atoms on the electrode surface. In addition, electrolysis using various electrolyte solutions confirmed that the influence of dopants on the BNDD electrode surface was significant for CO2RR, particularly at low overpotentials.

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Enhancement of the Catalytic Effect on the Electrochemical Conversion of CO<inf>2</inf> to Formic Acid Using MXene (Ti<inf>3</inf>C<inf>2</inf>T<inf>x</inf>)-Modified Boron-Doped Diamond Electrode

Jiwanti P.K., Alfaza A.M., Kadja G.T.M., Natalya S.A.C., Sagita F., Einaga Y., Purwaningsih A., Amalina I., Rizki I.N.

Energies (Energies) 16 ( 12 ) 2023.06

The rising concentration of carbon dioxide (CO2) as one of the greenhouse gases in the atmosphere is a major source of worry. Electrochemical reduction of CO2 is one of many ways to convert CO2 gas into usable compounds. An electrochemical technique was applied in this study to reduce CO2 using a boron-doped diamond (BDD) working electrode modified with MXene (Ti3C2Tx) material to improve electrode performance. MXene concentrations of 0.5 mg/mL (MXene-BDD 0.5), 1.0 mg/mL (MXene-BDD 1.0), and 2.0 mg/mL (MXene-BDD 2.0) were drop-casted onto the BDD surface. MXene was effectively deposited on top of the BDD surface, with Ti weight loads of 0.12%, 4.06%, and 7.14% on MXene-BDD 0.5, MXene-BDD 1.0, and MXene-BDD 2.0, respectively. The modified working electrode was employed for CO2 electroreduction with optimal CO2 gas aeration. The existence of the MXene substance in BDD reduced the electroreduction overpotential of CO2. For the final result, we found that the MXene-BDD 2.0 electrode effectively generated the most formic acid product with a maximum reduction potential as low as −1.3 V (vs. Ag/AgCl).

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Electrogenerated chemiluminescence at boron-doped diamond electrodes

Fiorani A., Valenti G., Paolucci F., Einaga Y.

Chemical Communications (Chemical Communications) 59 ( 51 ) 7900 - 7910 2023.05

ISSN 13597345

Electrogenerated chemiluminescence (ECL) refers to the phenomenon of light emission from molecular species which is triggered by an electrochemical reaction. Therefore, like most electrochemical systems, the electrode material plays a pivotal role and much effort has been made in order to find the best material for ECL, in terms of light signal intensity and long-term stability, especially after the development of ECL for analytical applications. In this article, we will introduce and highlight the distinctive features of boron-doped diamond (BDD) as an electrode material for ECL which has complementary properties compared to the most common metals (e.g., Au or Pt) and carbon materials (e.g., glassy carbon, carbon nanotubes and graphene). Boron-doped diamond electrodes emerged as novel electrodes, gaining more and more interest from the electrochemical community for their peculiar characteristics such as a wide solvent window, low capacitance, resistance to fouling and mechanical robustness. Furthermore, compared to metal electrodes, BDD does not form an oxide layer in aqueous solutions, and the sp3 carbon hybridization gives BDD the ability to enable peculiar electrochemical reactions that are not possible on sp2 carbon materials. Electrogenerated chemiluminescence investigations with boron-doped diamond electrodes have been reported for common ECL systems (luminophores and co-reactants), and special ECL that is only possible on BDD which includes the in situ electrochemical generation of the co-reactant.

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A strategy for low-cost portable monitoring of plasma drug concentrations using a sustainable boron-doped-diamond chip

Saiki T., Ogata G., Sawamura S., Asai K., Razvina O., Watanabe K., Kato R., Zhang Q., Akiyama K., Madhurantakam S., Ahmad N.B., Ino D., Nashimoto H., Matsumoto Y., Moriyama M., Horii A., Kondo C., Ochiai R., Kusuhara H., Saijo Y., Einaga Y., Hibino H.

Heliyon (Heliyon) 9 ( 5 ) 2023.05

ISSN 24058440

On-site monitoring of plasma drug concentrations is required for effective therapies. Recently developed handy biosensors are not yet popular owing to insufficient evaluation of accuracy on clinical samples and the necessity of complicated costly fabrication processes. Here, we approached these bottlenecks via a strategy involving engineeringly unmodified boron-doped diamond (BDD), a sustainable electrochemical material. A sensing system based on a ∼1 cm2 BDD chip, when analysing rat plasma spiked with a molecular-targeting anticancer drug, pazopanib, detected clinically relevant concentrations. The response was stable in 60 sequential measurements on the same chip. In a clinical study, data obtained with a BDD chip were consistent with liquid chromatography–mass spectrometry results. Finally, the portable system with a palm-sized sensor containing the chip analysed ∼40 μL of whole blood from dosed rats within ∼10 min. This approach with the ‘reusable’ sensor may improve point-of-monitoring systems and personalised medicine while reducing medical costs.

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Electrochemical CO<inf>2</inf> reduction to CO facilitated by reduced boron-doped diamond

Du J., Fiorani A., Einaga Y.

Diamond and Related Materials (Diamond and Related Materials) 135 2023.05

ISSN 09259635

In the mechanistic investigations of electrochemical CO2 reduction reaction (eCO2RR), the undercoordinated site and oxidized metals are generally considered the most likely sources of catalytic sites. However, in the eCO2RR on boron-doped diamond (BDD) electrodes, metal centers are not available, and undercoordinated sites from boron doping did not demonstrated a favorable effect on the catalytic activity. By means of electrochemical activation, we found that when the surface of BDD electrodes is in a stable reduced state, the catalytic activity of eCO2RR for CO production is optimal. The Faradaic efficiency for CO production was increased up to 64 %, and the corresponding production rate reached 23 μmol cm−2 h−1, which was more than three times of the non-activated BDD set as comparison. This work demonstrates that the catalytic activity for eCO2RR can also originate from a reduced surface of BDD electrode.

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Development of an Acrylamide Biosensor Using Guanine and Adenine as Biomarkers at Boron-Doped Diamond Electrodes: Integrated Molecular Docking and Experimental Studies

Anggraini L.E., Rahmawati I., Nasution M.A.F., Jiwanti P.K., Einaga Y., Ivandini T.A.

Bulletin of the Chemical Society of Japan (Bulletin of the Chemical Society of Japan) 96 ( 5 ) 420 - 428 2023.05

ISSN 00092673

An acrylamide biosensor was developed by utilizing purine bases, i.e. guanine and adenine, through computational and electrochemical approaches. The molecular docking simulation proved that interaction of double-stranded DNA with the purine bases has the lowest Gibbs binding free energy compared to other biomolecules with a ΔGbinding of -4.2759 kcal/mol. Meanwhile, cyclic voltammetry of both guanine and adenine in 0.1M phosphate buffer solution at pH 7.4 using a boron-doped diamond electrode showed an irreversible oxidation peak in the potential range of 0 to +1.8V (vs. Ag/AgCl), confirming that the oxidation reaction was irreversible. The current of these peaks decreased linearly with the concentration of acrylamide due to the adduct formation between the purine bases and acrylamide. The formation of acrylamide adducts between acrylamide and purine bases was confirmed by the shift of the peak wavelength of the UV spectrum from 260 to 257 nm. The use of guanine for acrylamide sensing showed a linear calibration curve in the concentration range of 0.20-1.00 μM (R2 = 0.99) with a limit of detection and limit of quantification attained at 0.11 and 0.36 μM, respectively. In the case of adenine, a linear calibration curve was observed in the concentration range of 0.14-1.00 μM (R2 = 0.99) with a limit of detection and limit of quantification of 0.10 and 0.34 μM, respectively. The developed method was successfully performed for the acrylamide determination in coffee samples and was validated by HPLC.

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Spin Manipulation in a Metal–Organic Layer through Mechanical Exfoliation for Highly Selective CO<inf>2</inf> Photoreduction

Wu D., Yin H.Q., Wang Z., Zhou M., Yu C., Wu J., Miao H., Yamamoto T., Zhaxi W., Huang Z., Liu L., Huang W., Zhong W., Einaga Y., Jiang J., Zhang Z.M.

Angewandte Chemie - International Edition (Angewandte Chemie - International Edition) 62 ( 18 ) 2023.04

ISSN 14337851

Spin manipulation of transition-metal catalysts has great potential in mimicking enzyme electronic structures to improve activity and/or selectivity. However, it remains a great challenge to manipulate room-temperature spin state of catalytic centers. Herein, we report a mechanical exfoliation strategy to in situ induce partial spin crossover from high-spin (s=5/2) to low-spin (s=1/2) of the ferric center. Due to spin transition of catalytic center, mixed-spin catalyst exhibits a high CO yield of 19.7 mmol g−1 with selectivity of 91.6 %, much superior to that of high-spin bulk counterpart (50 % selectivity). Density functional theory calculations reveal that low-spin 3d-orbital electronic configuration performs a key function in promoting CO2 adsorption and reducing activation barrier. Hence, the spin manipulation highlights a new insight into designing highly efficient biomimetic catalysts via optimizing spin state.

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Development of Ofloxacin Electrochemical Sensor in Milk Sample using Boron-doped Diamond Electrode Decorated by Zinc Nanoparticles

Jiwanti P.K., Hendri M., Wafiroh S., Einaga Y.

Analytical and Bioanalytical Electrochemistry (Analytical and Bioanalytical Electrochemistry) 15 ( 4 ) 280 - 293 2023.04

The study of Ofloxacin (OFL) electrochemical sensor on the surface of zinc modified boron-doped diamond (Zn-BDD) electrode is reported. OFL has been known as one of the fluoroquinolone antibiotics which is used in treating infectious diseases and also in animal agriculture. Despite its effectiveness, long-term consumption could promote antimicrobial resistance. Therefore, a sensitive and selective detection method is important. Meanwhile, BDD has been known for its low background current and high stability, in which, it is necessary for sensor application. Besides, Zn nanoparticles have been widely used for sensor applications due to their low toxicity and low cost. In this work, Zn-BDD electrode was prepared through electrodeposition. The S/B value and sensitivity for OFL analysis were 9.5 and 0.42 respectively on Zn-BDD, in which, it is higher compared to the use of a bare BDD electrode. The analysis in milk was possible with the recovery of 83.05% and 101.20% for BDD and Zn-BDD electrodes respectively. It is suggested that Zn-BDD electrode could be applied for OFL analysis for further real application.

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Low-interference norepinephrine signal on dopamine detection using nafion-coated boron doped diamond electrodes

Irkham , Nasa K., Kurnia I., Hartati Y.W., Einaga Y.

Biosensors and Bioelectronics (Biosensors and Bioelectronics) 220 2023.01

ISSN 09565663

The detection of dopamine in the presence of norepinephrine using nafion-coated boron doped diamond (Nafion-BDD) electrodes was presented. An increase current signal for dopamine could be observed at around 0.75 V using Nafion-BDD, while a change in the current signal of norepinephrine that appears at similar potential was not observed. This might be due to electronegativity of the norepinephrine that is not positive enough to be attracted towards the nafion membrane, albeit neutral enough to pass through the membrane and undergo electrochemical oxidation. An optimization process including accumulation time of dopamine inside the nafion layer, solution of the pH, and nafion thickness was conducted to exploit the difference electrochemical behavior between those two catecholamines at the Nafion-BDD. Using an accumulation time of 300 s, solution pH of 7, and nafion thickness of 1.1 μm, dopamine's LOD was found to be 0.966 μM. Low-interference signal of norepinephrine to the dopamine could be observed with an excellent %recovery of dopamine in 5% range when the concentration of norepinephrine was 10 times lower compared to dopamine concentration.

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Selective electro-oxidation of cumene utilizing a flow reactor equipped with diamond electrodes

Nihongi S., Matsuoka R., Saitoh T., Einaga Y., Yamamoto T.

Current Research in Green and Sustainable Chemistry (Current Research in Green and Sustainable Chemistry) 7 2023.01

Although oxidation of benzylic C(sp3)−H bonds is an important process for synthesizing biologically active compounds, the reactions generically require hazardous reagents, catalysts, and harsh conditions. Since electro-organic synthesis utilizes electricity itself as a reagent, reactions can proceed well even under ambient conditions. Herein, we report a selective oxidation of cumene in an electrochemical flow reactor. Cumyl alcohol was selectively obtained under optimum amount of charge and current density. The selective oxidation of cumene to cumyl alcohol was achieved because overoxidation of cumyl alcohol into acetophenone was suppressed by the electrochemical flow reactor.

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Photo-assisted electrochemical CO<inf>2</inf> reduction at a boron-doped diamond cathode

Iwai G., Fiorani A., Du J., Einaga Y.

Energy Advances (Energy Advances) 2023

We report on the coupling of photoelectrochemical water oxidation and electrochemical CO2 reduction to formic acid for a photoelectrochemical system capable of light and electrochemical energy conversion to chemical energy. Titanium oxide nanotubes (TiO2 NT) and boron-doped diamond (BDD) electrodes were used as a photoanode and a cathode, respectively. From CO2 electrochemical reduction at BDD, formic acid was obtained with a faradaic efficiency of about 86% and the system provided an overall energy conversion efficiency of 5.5%. From previous CO2 reduction at a dark electrolyzer based on a BDD cathode, the cell voltage was reduced from 2.7 V to 1.4 V with 52% saving of the electrical energy input. This resulted in an increase from 50% to nearly 80% of electrical-to-chemical energy conversion efficiency.

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The Dependence of Boron Concentration in Diamond Electrode for Ciprofloxacin Electrochemical Sensor Application

Savitri I.N.I., Jiwanti P.K., Putri I.Z.D., Irkham I., Einaga Y., Supriyanto G., Wong Y.H., Srivastava S.K., Abdullah C.A.C.

Indonesian Journal of Chemistry (Indonesian Journal of Chemistry) 23 ( 3 ) 809 - 822 2023

ISSN 14119420

This study investigates the effects of boron concentration on boron-doped diamond (BDD) electrodes for electrochemical sensors of ciprofloxacin. The effects of boron concentration, scan rate, and pH of BDD electrodes with boron concentrations of 0.1, 0.5, and 1% were examined to determine the optimal conditions. Furthermore, square wave voltammetry (SWV) in phosphate buffer pH 7 was used to analyze the electrochemical behavior of ciprofloxacin. The results revealed a linear calibration curve in the concentration range of 30–100 μM with a recovery of 85–110%. Meanwhile, BDD electrode with the highest boron concentration in this experiment (1%) showed a very low limit of detection of 0.17 μM, meaning that 1% BDD gave a highly sensitive and significant measurement result for the electrochemical sensor of ciprofloxacin. With the results given, this study provides new insights for controlling boron concentrations in diamond electrodes for the electrochemical sensors of quinolone antibiotics.

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Modification of Screen-printed Carbon Electrodes with Gold Particles to Enhance Luminol Electrochemiluminescence for Hydrogen Peroxide Detection

Syukur J.M., Rahmawati I., Sanjaya A.R., Ridwan M., Fiorani A., Einaga Y., Ivandini T.A.

Sensors and Materials (Sensors and Materials) 35 ( 5 ) 1785 - 1799 2023

ISSN 09144935

Screen-printed carbon electrodes (SPCEs) were modified with gold particles to improve luminol electrochemiluminescence (ECL) in the presence of H2O2 as the co-reactant. Gold particles with sizes ranging from 10 to 50 nm were successfully deposited by the electrochemical technique with around 3.4% (w/w) gold on the carbon surface. The gold-modified SPCE (Au-SPCE) increases the ECL intensity of luminol around 2.5 times more than that using the unmodified SPCE. These signals were also found to be linearly correlated to H2O2 concentration. At an optimum pH of 9, the ECL signals of 1 mM luminol in 0.1 M phosphate buffer solution using the Au-SPCE are linear in the H2O2 concentration range from 0.5 to 200 µM (R2 = 0.99) with an estimated detection limit of 4.78 µM. The developed sensor also showed the excellent repeatability and reproducibility of the ECL signals. Moreover, H2O2 detection in milk and tap water samples was also successfully demonstrated, indicating that the developed sensor is promising for H2O2 detection applications.

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Boron-Doped Diamond Electrodes: Fundamentals for Electrochemical Applications

Einaga Y.

Accounts of Chemical Research (Accounts of Chemical Research) 55 ( 24 ) 3605 - 3615 2022.12

ISSN 00014842

ConspectusBoron-doped diamond (BDD) electrodes have emerged as next-generation electrode materials for various applications in electrochemistry such as electrochemical sensors, electrochemical organic synthesis, CO2 reduction, ozone water generation, electrochemiluminescence, etc. An optimal BDD electrode design is necessary to realize these applications. The electrochemical properties of BDD electrodes are determined by important parameters such as (1) surface termination, (2) surface orientation, and (3) boron doping level.In this Account, we discuss how these parameters contribute to the function of BDD electrodes. First, control of the surface termination (hydrogen/oxygen) is described. The electrochemical conditions such as the solution pH and the application potential were studied precisely. It was confirmed that an acidic solution and the application of negative potential accelerate hydrogenation, and the mechanism behind this is discussed. For oxygenation, we directly observed changes in surface functional groups by in situ attenuated total reflection infrared spectroscopy and electrochemical X-ray photoelectron spectroscopy measurements.Next, the difference in surface orientation was examined. We prepared homoepitaxial single-crystal diamond electrodes comprising (100) and (111) facets with similar boron concentrations and resistivities and evaluated their electrochemical properties. Experimental results and theoretical calculations revealed that (100)-oriented single-crystal BDD has a wider space charge layer than (111)-oriented BDD, resulting in a slower response. Furthermore, isolated single-crystal microparticles of BDD with exposed (100) and (111) crystal facets were grown, and we studied the electrochemical properties of the respective facets by combination with hopping-mode scanning electrochemical cell microscopy.We also systematically investigated how the boron concentration and sp2 species affect the electrochemical properties. The results showed that the appropriate composition (boron and sp2 species level) is dependent on the application. The transmission electron microscopy images and electron energy loss spectra of highly boron-doped BDD are shown, and the relationship between the composition and electrochemical properties is discussed. Finally, we investigated in detail the effect of the sp2 component on low-doped BDD. Surprisingly, although the sp2 component is usually expected to induce a narrowing of the potential window and an increase in the charging current, low-doped BDD showed the opposite trend depending on the degree of sp2 carbon.The results and discussion presented in this Account will hopefully promote a better understanding of the fundamentals of BDD electrodes and be useful for the optimal development of electrodes for future applications.

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Boron-Doped Diamond as a Quasi-Reference Electrode

Peng Z., Fiorani A., Akai K., Murata M., Otake A., Einaga Y.

Analytical Chemistry (Analytical Chemistry) 94 ( 48 ) 16831 - 16837 2022.12

ISSN 00032700

As a working electrode, boron-doped diamond (BDD) has been studied in detail in electrochemical processes because of its superior electrochemical properties. However, these characteristics have rarely been mentioned when BDD is used as a quasi-reference electrode (QRE). Herein, we conducted a systematic investigation on BDD electrodes, with different boron-doping levels (1 and 0.1%) and different surface terminations (hydrogen and oxygen) for their application as a QRE. A BDD electrode with 1% boron and a hydrogen-terminated surface achieved the best stability. Its open-circuit potential (OCP) exhibited less than 100 mV of potential drift over 6000 s and showed a minuscule half-wave potential difference (E1/2) of 0.0037 V in 0.1 mM K3[Fe(CN)6]/1 M KCl solution before and after the OCP measurement. Based on these observations, anions are found to contribute to the potential, which we preliminarily speculate as related to the capacitance caused by electrostatic adsorption on the positively charged hydrogen-terminated surface. The repeatability of measurement was verified through continuous cyclic voltammetry tests in 0.1 mM K3[Fe(CN)6]/1 M KCl, showing a maximum E1/2 difference of 0.042 V. The contribution of the redox couples was excluded, and the repeatability was considered to originate from its surface stability. Finally, a linear response of the optimized BDD as a QRE was validated (R2 > 0.99) by determination of free chlorine and dopamine concentrations, respectively. These results consolidate the existing fundamental research on BDD electrodes and promote the possibility of its application as a QRE in harsh environments or in vivo biological monitoring.

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Electrochemical detection of triamterene in human urine using boron-doped diamond electrodes

Ishii K., Ogata G., Einaga Y.

Biosensors and Bioelectronics (Biosensors and Bioelectronics) 217 2022.12

ISSN 09565663

Urine is one of the most used biological fluids for screening drug delivery and the resultant metabolites. In sports, the use of diuretics such as triamterene is considered a violation of anti-doping rules and is stipulated to be present at less than 79 nM in urine by the World Anti-Doping Agency (WADA). It is therefore important to develop effective rapid and low-cost tests for this diuretic. Here we apply electrochemical analysis using boron-doped diamond (BDD) electrodes, which have superior properties such as low background current, a wide potential window, and high resistance to deactivation. Since real urine samples show clear oxidation current peaks in the potential range more positive than 0.5 V (vs. Ag/AgCl) due to the presence of bio-components such as protein, uric acid, and ascorbic acid, to detect triamterene effectively, the electrochemical protocol was optimized towards a potential range where the other components have limited effect. Our results show that reduced triamterene exhibits an oxidation peak at 0.1 V (vs. Ag/AgCl) in 0.1 M phosphate buffer (PB) and at 0.2 V (vs. Ag/AgCl) in pooled human urine. The peak current value increased according to the triamterene concentration. The limit of detection (LOD) was 3.15 nM in the PB and 7.80 nM in pooled human urine. Finally, triamterene detection was attempted in individual urine samples. Triamterene was electrochemically detectable in individual urine samples, excluding urine samples containing an excess amount of ascorbic acid. The limit of detection (LOD) in individual urine samples was determined to be 20.8 nM.

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Application of boron doped diamond electrodes to electrochemical gas sensor

Triana Y., Ogata G., Einaga Y.

Current Opinion in Electrochemistry (Current Opinion in Electrochemistry) 36 2022.12

ISSN 24519103

Boron-doped diamond (BDD) electrodes have been attracting attention as superior electrode materials for electrochemical sensing applications. Here, we focused on applications of the BDD electrodes to electrochemical gas sensing especially dissolved gas in aqueous solution. This article discusses arsine, hydrogen sulfide, nitrogen dioxide gas for environmental sensing, and oxygen in the blood for biomedical sensing. The analytical performances suggest that BDD electrodes are more than adequate for determining the concentration of these gas species.

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Amine-Functionalized Diamond Electrode for Boosting CO<inf>2</inf>Reduction to CO

Mikami T., Yamamoto T., Tomisaki M., Einaga Y.

ACS Sustainable Chemistry and Engineering (ACS Sustainable Chemistry and Engineering) 10 ( 45 ) 14685 - 14692 2022.11

Carbon capture, utilization, and storage (CCUS) have been attracting much attention as an initiative to achieve carbon neutrality. In the capture and storage strategy, amines are widely used for highly efficient separation and capturing of CO2since amines react with CO2to form carbamates. In the utilization strategy, CO2electroreduction is a promising method to convert CO2into value-added compounds because reaction conditions are relatively mild and easily controlled. In this work, toward combining CO2capture and storage technologies and CO2electroreduction, we focused on amine modification of the electrode surface, in which boron-doped diamond (BDD) was chosen as a sustainable electrode material. CO2electroreduction using the amine-modified BDD was performed, and an applied potential dependence of the product selectivity was examined. In situ attenuated total reflectance-infrared measurements showed that the peak intensity of the stretching vibration of the carbonyl group at around 1640 cm-1decreased as applied potentials became more negative. The effect of amine modification of the BDD surface lies in the formation of a C-N bond during CO2electroreduction, resulting in the enhancement of the selectivity of CO production up to 8 times compared to the unmodified BDD.

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Activation of Boron-Doped Diamond Electrodes for Electrochemical CO<inf>2</inf>Reduction in a Halogen-free Electrolyte

Otake A., Du J., Einaga Y.

ACS Sustainable Chemistry and Engineering (ACS Sustainable Chemistry and Engineering) 10 ( 44 ) 14445 - 14450 2022.11

The electrochemical reduction of carbon dioxide (CO2) has been attracting great interest in these days. In particular, the electrochemical production of formic acid from carbon dioxide in a halogen-free electrolyte is practically important for recently developed applications such as hydrogen carriers and fuel cells. In the present work, we have demonstrated highly selective electrochemical CO2 reduction in a halogen-free electrolyte by an "activation"process which involves an initial electrochemical CO2 reduction reaction at a boron-doped diamond (BDD) electrode. The BDD activation increased the Faradaic efficiency of formic acid from 10 to 90%. A mechanistic study on the BDD activation is presented, which can explain the drastic change of reaction selectivity from the perspective of reducing the energy of electron transfer from the BDD electrode and the mass transport of CO2 molecules to the electrode surface.

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Convection control in a flow cell on electrochemical CO<inf>2</inf> reduction using a boron-doped diamond electrode

Nihongi S., Otake A., Du J., Einaga Y.

Carbon (Carbon) 200 456 - 461 2022.11

ISSN 00086223

While it is well recognized that mass transfer is an important factor in electrochemical reactions, the influence of mass transfer, especially of the convection on the electrochemical CO2 reduction has not been investigated. In this study, we focused on the influence of convection in a flow cell system using a boron-doped diamond electrode. The results clearly showed that convection improved the product selectivity and electrode potentials in CO2 reduction. It suggested that convection controls CO2 mass transfer in a flow cell system and influences the reactivity of electrochemical CO2 reduction.

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Photophysics and electrochemistry of ruthenium complexes for electrogenerated chemiluminescence

Villani E., Sakanoue K., Einaga Y., Inagi S., Fiorani A.

Journal of Electroanalytical Chemistry (Journal of Electroanalytical Chemistry) 921 2022.09

ISSN 15726657

Electrogenerated chemiluminescence, or electrochemiluminescence (ECL), is nowadays a powerful transduction method in electroanalysis, in particular regarding the application in clinical diagnostics. Indeed, its superior capability relies in the fruitful combination of electrochemical and photoluminescence properties. The research on efficient ECL luminophores has brought a wide range of molecules, form organic systems to inorganic complexes, however, despite this large pool of luminophores available, tris(2,2′-bipyridine)ruthenium (II) [Ru(bpy)3]2+ is still leading since the first report in 1972, in both academic research and commercially available systems. To acknowledge the outmost importance of this inorganic complex, here we report the photophysical and electrochemical properties of [Ru(bpy)3]2+ and its derivatives obtained by ligand design for application in ECL.

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A rapid and simple electrochemical detection of the free drug concentration in human serum using boron-doped diamond electrodes

Moriyama H., Ogata G., Nashimoto H., Sawamura S., Furukawa Y., Hibino H., Kusuhara H., Einaga Y.

Analyst (Analyst) 147 ( 20 ) 4442 - 4449 2022.09

ISSN 00032654

Monitoring drug concentration in blood and reflecting this in the dosage are crucial for safe and effective drug treatment. Most drug assays are based on total concentrations of bound and unbound proteins in the serum, although only the unbound concentration causes beneficial and adverse events. Monitoring the unbound concentration alone is expected to provide a means for further optimisation of drug treatment. However, unbound concentration monitoring has not been routinely used for drug treatment due to the long analysis time and the high cost of conventional methods. Here, we have developed a rapid electrochemical method to determine the unbound concentration in ultrafiltered human serum using boron-doped diamond (BDD) electrodes. When the anticancer drug doxorubicin was used as the test drug, the catalytic doxorubicin-mediated reduction of dissolved oxygen provided a sensitive electrochemical signal, with a detection limit of 0.14 nM. In contrast, the sensitivity of glassy carbon (GC) was inferior under the same conditions due to interference from the dissolved oxygen reduction current. The signal background ratio (S/B) of BDD and GC was 11.5 (10 nM doxorubicin) and 1.1 (50 nM), respectively. The results show that a fast measurement time within ten seconds is possible in the clinical concentration range. Additionally, in the ultrafiltered human serum, the obtained values of unbound doxorubicin concentration showed good agreement with those quantified by conventional liquid chromatography-mass spectrometry. This approach has the potential for application in clinical settings where rapid and simple analysis methods would be beneficial.

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Detection of dissolved hydrogen in water using platinum-modified boron doped diamond electrodes

Irkham , Kazama K., Einaga Y.

Journal of Electroanalytical Chemistry (Journal of Electroanalytical Chemistry) 917 2022.07

ISSN 15726657

The detection of molecular hydrogen in water using platinum modified boron doped diamond (Pt-BDD) was presented. A clear peak of hydrogen desorption was observed around −0.1 V in 0.1 M KCl solution. With a simple electrochemical pretreatment, the signal at Pt-BDD electrode was found to be higher and more stable compared to those using bare Pt electrode. The performance of the sensor was compared with gas chromatography method. The result shows a similar trend with either same or different concentration of H2. Lastly, the measurement was successfully conducted in the tap water even without addition of electrolyte. These result shows that Pt-BDD could be promoted as a good electrode candidate for sensing dissolved H2 in the water-based solution.

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Enzymatic Biosensors with Electrochemiluminescence Transduction

Rahmawati I., Einaga Y., Ivandini T.A., Fiorani A.

ChemElectroChem (ChemElectroChem) 9 ( 12 ) 2022.06

Sensors rely on a plurality of transduction methods, and among the available selections, electrochemical techniques offer the peculiar advantage of an easy interfacing between biological recognition elements and electronic signal transduction processes. Furthermore, electrochemical devices are qualified for decentralized point-of-care testing as they can be easily downsized and made at low cost for a wide range of potential applications, for example biomedical or environmental. Electrochemical methods of transduction differ for the technique used, as it can be voltammetry, chronoamperometry, impedance spectroscopy, or electrochemiluminescence. The latter is peculiar among electrochemical techniques since in electrochemiluminescence the analytical signal is light emission, and this offers several advantages, mainly related to background suppression and detection limit, combined with fast measurement. This review introduces the principles of enzyme biosensors coupled with electrochemiluminescence transduction, summarises the research, and finally highlights the strategies to take full advantage of this detection method.

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A New Pathway for CO<inf>2</inf>Reduction Relying on the Self-Activation Mechanism of Boron-Doped Diamond Cathode

Du J., Fiorani A., Inagaki T., Otake A., Murata M., Hatanaka M., Einaga Y.

JACS Au (JACS Au) 2 ( 6 ) 1375 - 1382 2022.06

By means of an initial electrochemical carbon dioxide reduction reaction (eCO2RR), both the reaction current and Faradaic efficiency of the eCO2RR on boron-doped diamond (BDD) electrodes were significantly improved. Here, this effect is referred to as the self-activation of BDD. Generally, the generation of carbon dioxide radical anions (CO2•-) is the most recognized pathway leading to the formation of hydrocarbons and oxygenated products. However, the self-activation process enabled the eCO2RR to take place at a low potential, that is, a low energy, where CO2•- is hardly produced. In this work, we found that unidentate carbonate and carboxylic groups were identified as intermediates during self-activation. Increasing the amount of these intermediates via the self-activation process enhances the performance of eCO2RR. We further evaluated this effect in long-term experiments using a CO2 electrolyzer for formic acid production and found that the electrical-to-chemical energy conversion efficiency reached 50.2% after the BDD self-activation process.

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Electrogenerated chemiluminescence of luminol at a boron-doped diamond electrode for the detection of hypochlorite

Rahmawati I., Saepudin E., Fiorani A., Einaga Y., Ivandini T.A.

Analyst (Analyst) 147 ( 12 ) 2696 - 2702 2022.04

ISSN 00032654

Electrogenerated chemiluminescence (ECL) of luminol at a boron-doped diamond electrode has been used for hypochlorite determination. The presence of H2O2 induces the generation of the ECL signals of luminol. In contrast, the presence of hypochlorite oxidizes luminol directly to decrease the ECL signals of luminol. Accordingly, a decrease of the ECL signals of luminol in the presence of H2O2 was used as the signal response for hypochlorite detection. A linear decrease of ECL signals with the NaClO concentration in the range from 0 to 20 μM was observed with a sensitivity of 18.56 a.u. μM−1 cm−2. An estimated detection limit of 0.88 μM was achieved, which is around one order lower than the detection limit obtained using the normal electrochemical method with the same electrode. The system also provides a good selectivity towards Cu2+ and Na+. A reproducibility of 3.40%RSD was noted for 15 repetitive measurements. The analytical performance was found to be favourable in comparison to those of other typical electrochemical and electrochemiluminescence methods, indicating that it is applicable for real sample detection.

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Boron-Doped Diamond Electrode Outperforms the State-of-the-Art Electrochemiluminescence from Microbeads Immunoassay

Sakanoue K., Fiorani A., Santo C.I., Irkham , Valenti G., Paolucci F., Einaga Y.

ACS Sensors (ACS Sensors) 7 ( 4 ) 1145 - 1155 2022.04

Electrochemiluminescence (ECL) is a powerful transduction technique where light emission from a molecular species is triggered by an electrochemical reaction. Application to biosensors has led to a wide range of electroanalytical methods with particular impact on clinical analysis for diagnostic and therapeutic monitoring. Therefore, the quest for increasing the sensitivity while maintaining reproducible and easy procedures has brought investigations and innovations in (i) electrode materials, (ii) luminophores, and (iii) reagents. Particularly, the ECL signal is strongly affected by the electrode material and its surface modification during the ECL experiments. Here, we exploit boron-doped diamond (BDD) as an electrode material in microbead-based ECL immunoassay to be compared with the approach used in commercial instrumentation. We conducted a careful characterization of ECL signals from a tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)32+)/tri-n-propylamine (TPrA) system, both homogeneous (i.e., free diffusing Ru(bpy)32+) and heterogeneous (i.e., Ru(bpy)32+bound on microbeads). We investigated the methods to promote TPrA oxidation, which led to the enhancement of ECL intensity, and the results revealed that the BDD surface properties greatly affect the ECL emission, so it does the addition of neutral, cationic, or anionic surfactants. Our results from homogeneous and heterogeneous microbead-based ECL show opposite outcomes, which have practical consequences in ECL optimization. In conclusion, by using Ru(bpy)32+-labeled immunoglobulins bound on microbeads, the ECL resulted in an increase of 70% and a double signal-to-noise ratio compared to platinum electrodes, which are actually used in commercial instrumentation for clinical analysis. This research infers that microbead-based ECL immunoassays with a higher sensitivity can be realized by BDD.

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Electrochemical Oxidation Behavior of Nitrogen Dioxide for Gas Detection Using Boron Doped Diamond Electrodes

Triana Y., Irkham , Einaga Y.

Electroanalysis (Electroanalysis) 34 ( 4 ) 752 - 760 2022.04

ISSN 10400397

The electrochemical oxidation reaction of nitrogen dioxide (NO2) using boron doped diamond (BDD) electrodes is presented. Cyclic voltammetry of NO2 in a 0.1 M KClO4 solution exhibits oxidation peaks at +1.1 V and +1.5 V (vs. Ag/AgCl) which are attributable to oxidation of HONO and NO2−, respectively. Moreover, the pH and scan rate dependences were investigated to study the oxidation mechanism. A linear calibration curve was observed in the concentration range of ∼1 to 5 mM (R2=0.99) with a detection limit of 11.1 ppb (S/B=3) for HONO and 58.6 ppb (S/B=3) for NO2−. In addition, the analytical performance was compared with those using glassy carbon, platinum and stainless steel as the working electrode.

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Simultaneous electrochemical detection of ozone and free chlorine with a boron-doped diamond electrode

Peng Z., Irkham N., Akai K., Murata M., Tomisaki M., Einaga Y.

Analyst (Analyst) 147 ( 8 ) 1655 - 1662 2022.03

ISSN 00032654

O3 and free chlorine play significant roles in disinfection and organic degradation. There are numerous reports about their mixed-use, yet detection of the residual concentrations is not easily accomplished, whilst the interactions between them remain unclear. Herein, we develop a detection method using a boron-doped diamond (BDD) electrode to achieve the simultaneous determination of O3 and free chlorine, which benefits from the unique property of the wide potential window of BDD electrodes. It is indicated that O3 can always be accurately determined at 0.35 V vs. Ag/AgCl in an acidic solution (pH = 4-5), whether or not free chlorine is present in the solution, whereas free chlorine can be precisely monitored at −0.78 V vs. Ag/AgCl only after the O3 is completely depleted. Furthermore, in a basic solution (pH = 9-10), the reduction peak of O3 at 0.57 V vs. Ag/AgCl promptly disappears accompanied by a decrease in the peak current of free chlorine at 1.41 V. All the phenomena observed in the acidic and basic solutions are concurrently confirmed in a quasi-neutral solution. Based on these complementary measurements, a mechanism is proposed, in which the O3 reduction results in partial oxidation of the BDD surface, hindering the reduction of free chlorine in the acidic mixture; whereas O3 reacts quickly with free chlorine in the basic solution, which causes the co-consumption of both of them. It is hoped these results will give us a guide as to how better utilize mixtures and more precisely simultaneously determine O3 and free chlorine in the mixture.

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Blood Oxygen Sensor Using a Boron-Doped Diamond Electrode

Triana Y., Ogata G., Tomisaki M., Irkham , Einaga Y.

Analytical Chemistry (Analytical Chemistry) 94 ( 9 ) 3948 - 3955 2022.03

ISSN 00032700

The electrochemical behavior of oxygen (O2) in blood was studied using boron-doped diamond (BDD) electrodes. Cyclic voltammogram of O2 in a 0.1 M phosphate buffer solution solution containing 1 × 10-6 M of bovine hemoglobin exhibits a reduction peak at -1.4 V (vs Ag/AgCl). Moreover, the scan rate dependence was investigated to study the reduction reaction mechanism, which was attributable to the reduction of O2 to H2O2 via two electrons. A linear calibration curve was observed in the concentration range of 86.88-314.63 mg L-1 (R2 = 0.99) with a detection limit of 1.0 mg L-1 (S/B = 3). The analytical performance was better than those with glassy carbon or platinum electrodes as the working electrode. In addition, an application to bovine blood was performed. The O2 concentration in the blood measured on the BDD electrodes was compared to that measured using an OxyLite Pro fiber-optic oxygen sensor device. Both methods gave similar values of the O2 concentration in the range of ∼40 to 150 mmHg. This result confirms that BDD electrodes could potentially be used to detect the O2 concentration in blood.

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Electrochemical study of CO<inf>2</inf> reduction on Ti<inf>3</inf>C<inf>2</inf>T<inf>x</inf> modified boron-doped diamond electrode

Jiwanti P.K., Alfaza A.M., Kadja G.T.M., Khalil M., Einaga Y.

Inorganic Chemistry Communications (Inorganic Chemistry Communications) 137 2022.03

ISSN 13877003

The electrochemical reduction of CO2 has been attracted researcher attention around the world. There are many researches on how to improve the value of CO2 gas by converting it to useful chemicals or feedstock. In this report, we studied electrochemical behavior of Ti3C2Tx modified on the surface of boron-doped diamond (BDD) electrode for CO2 reduction. It is shown that the presence of Ti3C2Tx could improve the catalytic effect for CO2 reduction, as the CO2 reduction peak was shifted to positive potentials. This work is expected to provide an information of potential catalyst to be applied for real CO2 reduction application.

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Core-shell copper-gold nanoparticles modified at the boron-doped diamond electrode for oxygen sensors

Gunlazuardi J., Kurniawan A.D., Jiwanti P.K., Einaga Y., Ivandini T.A.

Analytical Methods (Analytical Methods) 14 ( 7 ) 726 - 733 2022.02

ISSN 17599660

Bimetallic copper-gold (Cu@Au) nanoparticles were synthesized and utilised to modify boron-doped diamond (BDD) electrodes. Nanorod particles with a diameter size of around 10 nm and a length of around 20 nm were successfully synthesized. These nanoparticles were then attached to the BDD surface by using allylamine as the bridge. Comparison among the BDD modified with Cu@Au and individual gold nanoparticles showed that Cu@Au nanoparticles created around 3 times higher gold coverage on the BDD surface than normal gold nanoparticles. It was also found that the use of allylamine as the bridge can attach more gold than copper nanoparticles. Moreover, around two times higher current responses of oxygen reduction reaction were observed at Cu@Au-modified BDD. Good linearity in a concentration range from 2 to 9 ppm could be achieved with a sensitivity of 0.0138 mA ppm-1 and limit detection of 1.98 ppm. An application of the modified BDD for a biochemical oxygen demand (BOD) sensor using Rhodotorula mucilaginosa UICC Y-181 as the biosensing agent was also demonstrated with glucose solutions as the solution model. Sensitivity equivalent to 17.4 μA mM-1 BOD could be achieved. The system showed good stability with an RSD of 3.45% in 10 measurements. This journal is

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Electrochemical Sensor of Levofloxacin on Boron-Doped Diamond Electrode Decorated by Nickel Nanoparticles

Jiwanti P.K., Sitorus I.R., Kadja G.T.M., Wafiroh S., Einaga Y.

Indonesian Journal of Chemistry (Indonesian Journal of Chemistry) 22 ( 5 ) 1321 - 1329 2022

ISSN 14119420

Levofloxacin (LEV) was known as one of the fluoroquinolone antibiotics that widely used as an antibacterial agent. Monitoring of LEV is important due to its negative side effect on humans. The determination of LEV was studied for the first time on nickel modified on a boron-doped diamond (NiBDD) electrode using the square wave voltammetry (SWV) method to improve the catalytic and sensitivity of the sensor. The response was linear in the range of 30–100 mM LEV. LEV sensor on NiBDD was found to be selective in the presence of urea, glucose, and ascorbic acid interferences. Good reproducibility with % a relative standard deviation of 1.45% (n = 10) was achieved. Therefore, the NiBDD electrode could be potentially applied for the real detection method of LEV.

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Application of Boron-doped Diamond Electrodes: Focusing on the Electrochemical Reduction of Carbon Dioxide

Einaga Y.

Electrochemistry (Electrochemistry) 90 ( 10 ) 2022

ISSN 13443542

Boron-doped diamond (BDD) electrodes are next generation electrode materials and their electrochemical applications have been actively developed in recent years. They are expected to be useful electrode materials for improving the environment and for bio-medical applications. Here, examples of practical applications as electrochemical sensors, the development of in vivo real time measurements, and electrochemical organic synthesis using BDD electrodes are briefly introduced. In the second part, our recent work on the production of useful chemicals by means of the electrochemical reduction of CO2 using BDD electrodes is described. The work has attracted particular attention for its potential contribution to carbon neutrality and carbon recycling.

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Electro-conversion of cumene into acetophenone using boron-doped diamond electrodes

Kitano M., Saitoh T., Nishiyama S., Einaga Y., Yamamoto T.

Beilstein Journal of Organic Chemistry (Beilstein Journal of Organic Chemistry) 18 1154 - 1158 2022

A straightforward electro-conversion of cumene into acetophenone has been reported using boron-doped diamond (BDD) electrodes. This particular conversion is driven by the addition reaction of a cathodically generated hydroperoxide anion to an anodically generated cumyl cation, where the BDD's wide potential window enables the direct anodic oxidation of cumene into the cumyl cation. Since electricity is directly employed as the oxidizing and reducing reagents, the present protocol is easy to use, suitable for scale-up, and inherently safe.

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Electrochemical CO<inf>2</inf> reduction on sub-microcrystalline boron-doped diamond electrodes

Peng Z., Xu J., Kurihara K., Tomisaki M., Einaga Y.

Diamond and Related Materials (Diamond and Related Materials) 120 2021.12

ISSN 09259635

Boron-doped diamond (BDD) electrodes are being increasingly investigated for application to electrochemical CO2 reduction. Previous, studies have mainly focused on microcrystalline (MC) BDD electrodes. In our study, we present an analysis of electrochemical CO2 reduction using sub-microcrystalline (SMC) BDD electrodes with different boron doping concentrations (0.28%, 0.11% and 0.03%). Unlike the microcrystalline case, these synthetic SMC BDD films with high sp2-bonded carbon do not show a boron-concentration dependence in terms of the activity of CO2 reduction to form formic acid (HCOOH). All the electrodes enabled efficient CO2 reduction at close to the maximum Faradaic efficiency for HCOOH in the range of 70% to 80%. From our observations, it is suggested that the sp2-bonded carbon should be crucial for the CO2 reduction. The results are hoped to enable a relaxation on the restrictions on the use of BDD electrodes towards industrial CO2 reduction application.

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NickelCobalt Modified Boron-Doped Diamond as an Electrode for a Urea/H<inf>2</inf>O<inf>2</inf> Fuel Cell

Putri Y.M.T.A., Jiwanti P.K., Irkham , Gunlazuardi J., Einaga Y., Ivandini T.A.

Bulletin of the Chemical Society of Japan (Bulletin of the Chemical Society of Japan) 94 ( 12 ) 2922 - 2928 2021.12

ISSN 00092673

Among many types of fuel cells, urea/H2O2 fuel cells have garnered attention from the scientific community due to the advantages of urea. In connection to this, a nickel-cobalt-modified boron-doped diamond (NiCo-BDD) electrode was prepared via chronoamperometry. A Ni/Co ratio of 4:1 in solution was determined as the optimum ratio for the urea oxidation reaction. Results showed that the Ni and Co particles were homogeneously deposited on the BDD surface and deposited without any interaction between the particles. The prepared NiCo-BDD electrode for a urea fuel cell showed optimum performance with a 0.1M KOH and 0.50M urea solution as the anode electrolyte and a 2.0M H2O2 and 2.0M H2SO4 solution as the cathode electrolyte. An opencircuit voltage of 0.817 V with a power density of approximately 0.632 mW/sq cm at room temperature and excellent stability after 6 hr of application were achieved. NiCo-BDD significantly enhanced the catalytic activity of urea oxidation reaction compared with the Ni plate, unmodified BDD, Ni-BDD, and Co-BDD.

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Localized Graphitization on Diamond Surface as a Manifestation of Dopants

Catalan F.C.I., Anh L.T., Oh J., Kazuma E., Hayazawa N., Ikemiya N., Kamoshida N., Tateyama Y., Einaga Y., Kim Y.

Advanced Materials (Advanced Materials) 33 ( 42 ) 2021.10

ISSN 09359648

Doped diamond electrodes have attracted significant attention for decades owing to their excellent physical and electrochemical properties. However, direct experimental observation of dopant effects on the diamond surface has not been available until now. Here, low-temperature scanning tunneling microscopy is utilized to investigate the atomic-scale morphology and electronic structures of (100)- and (111)-oriented boron-doped diamond (BDD) electrodes. Graphitized domains of a few nanometers are shown to manifest the effects of boron dopants on the BDD surface. Confirmed by first-principles calculations, local density of states measurements reveal that the electronic structure of these features is characterized by in-gap states induced by boron-related lattice deformation. The dopant-related graphitization is uniquely observed in BDD (111), which explains its electrochemical superiority over the (100) facet. These experimental observations provide atomic-scale information about the role of dopants in modulating the conductivity of diamond, as well as, possibly, other functional doped materials.

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Efficient photocatalytic conversion of benzene to phenol on stabilized subnanometer WO<inf>3</inf>quantum dots

Ohno A., Watanabe H., Matsui T., Somekawa S., Tomisaki M., Einaga Y., Oaki Y., Imai H.

Catalysis Science and Technology (Catalysis Science and Technology) 11 ( 19 ) 6537 - 6542 2021.10

ISSN 20444753

Band engineering with a quantum size effect is proposed to be utilized to design photocatalytic activity for the conversion of organic compounds. Subnanometer WO3 quantum dots (QDs) are spontaneously produced with the enhancement of the photocatalytic activity in a mesoporous silica matrix by preliminary photochemical dissolution. An appropriate upshift of the conduction band of subnanometer WO3 QDs stabilized by the coverage with the surface WO bonds promotes the efficient conversion of benzene to phenol without decomposition of the product into CO2 under ultraviolet illumination.

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Metal modified carbon-based electrode for CO<inf>2</inf> electrochemical reduction: A review

Jiwanti P.K., Sultana S., Wicaksono W.P., Einaga Y.

Journal of Electroanalytical Chemistry (Journal of Electroanalytical Chemistry) 898 2021.10

ISSN 15726657

The carbon-based electrode has been widely used for electrochemical analysis and synthesis. It is relatively inert for hydrogen evolution in the negative potential range, which is suitable for CO2 electrochemical reduction. In improving the catalytic activity, a modification of metal particles is commonly used on its surface. Various metal particles have been reported with multiple modification methods, including electrochemical and physical methods. In this report, the utilization of different metal particles, including metal oxide, metal hydroxide, and metal complexes, which are modified on carbon-based electrodes for CO2 electrochemical reduction application is specifically reviewed. This review is expected to provide comprehensive information on related topics.

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Effect of Boron-Doping Level and Surface Termination in Diamond on Electrogenerated Chemiluminescence

Sakanoue K., Fiorani A., Irkham , Einaga Y.

ACS Applied Electronic Materials (ACS Applied Electronic Materials) 3 ( 9 ) 4180 - 4188 2021.09

Electrogenerated chemiluminescence (ECL) is a phenomenon of light emission from a molecular species that is triggered by an electrochemical reaction. As with many electrochemical systems, ECL is highly dependent on the electrode material and its surface state. Boron-doped diamond (BDD) has been applied for ECL, however, thoughtful investigation remains scarce. In particular, a peculiar feature of BDD is the tuning of its properties by changing the amount of boron doping which in turn affects the electrochemical response. Here, we summarize the results from the most important ECL systems, such as Ru(bpy)32+(bpy = 2,2′-bipyridine)/tri-n-propylamine (TPrA), Ru(bpy)32+/S2O82-, Ru(bpy)32+/SO42-, Ru(bpy)32+/CO32-, and the luminol/CO32-system, by using BDD and correlating the doping level to the ECL response. We showed that the most suitable boron doping level and surface state are highly dependent on the ECL system investigated, highlighting the importance of the right choice of the BDD electrode. While focused on ECL systems, these results offer a general interpretation and might be adapted to different electrochemical systems where BDD finds application.

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Unique properties of fine bubbles in the electrochemical reduction of carbon dioxide using boron-doped diamond electrodes

Tomisaki M., Natsui K., Fujioka S., Terasaka K., Einaga Y.

Electrochimica Acta (Electrochimica Acta) 389 2021.09

ISSN 00134686

The electrochemical CO2 reduction on boron-doped diamond (BDD) electrodes in an aqueous solution with fine bubbles was studied. The overpotential decreased and the production of carbon monoxide was promoted in the CO2 reduction with fine bubbles compared to that without fine bubbles. It is suggested that fine bubbles in solution could facilitate the mass transport and also act as the catalyst for producing carbon monoxide. Potential-dependent in-situ attenuated total reflectance-infrared (ATR-IR) measurements confirmed the catalytic activity, showing that in solutions with CO2 fine bubbles the CO2•– intermediate or the CO2 molecules themselves become stabilized near the electrode and these can be adsorbed on the electrode surface more easily compared to using solutions without CO2 fine bubbles. The reported work is a first step in understanding the effects of fine bubbles in CO2 reduction reactions.

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Boron position-dependent surface reconstruction and electronic states of boron-doped diamond(111) surfaces: An: ab initio study

The Anh L., Catalan F.C.I., Kim Y., Einaga Y., Tateyama Y.

Physical Chemistry Chemical Physics (Physical Chemistry Chemical Physics) 23 ( 29 ) 15628 - 15634 2021.08

ISSN 14639076

Boron-doped diamond (BDD) has attracted much attention in semi-/superconductor physics and electrochemistry, where the surface structures and electronic states play crucial roles. Herein, we systematically examine the structural and electronic properties of the unterminated and H-terminated diamond(111) surfaces by using density functional theory calculations, and the effect of the boron position on them. The surface energy increases compared to that of the undoped case when the boron is located at a deeper position in the diamond bulk, which indicates that boron near the surface can facilitate the surface stability of the BDD in addition to the H-termination. Moreover, the surface energy and projected density of state analyses suggest that the boron can enhance the graphitization of the pristine (ideal) unterminated (111) surface thanks to the alternative sp2-sp3 arrangement on that surface. Finally, we found that surface electronic states depend on the boron's position, i.e., the Fermi energy (EF) is located around the mid-gap position when the boron lies near the surface, instead of showing a p-type semiconductor behavior where the EF lies closer to the valence band maximum. This journal is

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An efficient, formic acid selective CO<inf>2</inf>electrolyzer with a boron-doped diamond cathode

Du J., Fiorani A., Einaga Y.

Sustainable Energy and Fuels (Sustainable Energy and Fuels) 5 ( 10 ) 2590 - 2594 2021.05

We fabricated a CO2 electrolyzer in order to investigate the energy requirements and the electrical-to-chemical energy conversion efficiency obtained when using boron-doped diamond as the cathode. The main product in the electrochemical reduction of CO2 using a boron-doped diamond electrode is formic acid, with a faradaic efficiency of 96%. The electrical-to-chemical energy conversion efficiency was investigated at various bias voltages, and it reached 43%, very close to the predicted maximum value, at a cell voltage of 3 V. If the secondary products, hydrogen and carbon monoxide, are also considered, the total electrical-to-chemical energy conversion efficiency was as much as 45%. This journal is

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Modification of boron-doped diamond electrodes with gold-palladium nanoparticles for an oxygen sensor

Ivandini T.A., Luhur M.S.P., Khalil M., Einaga Y.

Analyst (Analyst) 146 ( 9 ) 2842 - 2850 2021.05

ISSN 00032654

Modification of boron-doped diamond (BDD) with gold-palladium nanoparticles (Au@PdNPs) was successfully performed. Prior to the modification, BDD was modified with allylamine to provide active sites for the attachment of nanoparticles, while the synthesis of Au@PdNPs was performed by chemical reduction of a palladium salt solution in a colloidal solution of gold nanoparticles. Characterization using TEM images showed that by controlling the palladium concentration, flower and core-shell shaped Au@PdNPs can be prepared. XPS studies confirmed that the nanoparticles with a flower shape could be attached better on the BDD surface. The Au@PdNPs-modified BDD (Au@PdNPs-BDD) electrodes were then examined for the oxygen reduction reaction in comparison with gold and palladium-based electrodes. One order higher current response was observed at Au@PdNPs-BDD compared to AuNPs-BDD, indicating the contribution of palladium in the oxygen reduction reaction. Good linearity with comparable limits of detection suggested that Au@PdNPs-BDD electrodes are promising for use as oxygen sensors. Furthermore, their application as BOD sensors was demonstrated.

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Analysis of Pharmacokinetics in the Cochlea of the Inner Ear

Sawamura S., Ogata G., Asai K., Razvina O., Ota T., Zhang Q., Madhurantakam S., Akiyama K., Ino D., Kanzaki S., Saiki T., Matsumoto Y., Moriyama M., Saijo Y., Horii A., Einaga Y., Hibino H.

Frontiers in Pharmacology (Frontiers in Pharmacology) 12 2021.05

Hearing loss affects >5% of the global population and therefore, has a great social and clinical impact. Sensorineural hearing loss, which can be caused by different factors, such as acoustic trauma, aging, and administration of certain classes of drugs, stems primarily from a dysfunction of the cochlea in the inner ear. Few therapeutic strategies against sensorineural hearing loss are available. To develop effective treatments for this disease, it is crucial to precisely determine the behavior of ototoxic and therapeutic agents in the microenvironment of the cochlea in live animals. Since the 1980s, a number of studies have addressed this issue by different methodologies. However, there is much less information on pharmacokinetics in the cochlea than that in other organs; the delay in ontological pharmacology is likely due to technical difficulties with accessing the cochlea, a tiny organ that is encased with a bony wall and has a fine and complicated internal structure. In this review, we not only summarize the observations and insights obtained in classic and recent studies on pharmacokinetics in the cochlea but also describe relevant analytical techniques, with their strengths, limitations, and prospects.

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Enhancing the Electrochemical Reduction of CO<inf>2</inf>by Controlling the Flow Conditions: An Intermittent Flow Reduction System with a Boron-Doped Diamond Electrode

Irkham , Nagashima S., Tomisaki M., Einaga Y.

ACS Sustainable Chemistry and Engineering (ACS Sustainable Chemistry and Engineering) 9 ( 15 ) 5298 - 5303 2021.04

Electrochemical CO2 reduction using an intermittent flow cell system with boron-doped diamond (BDD) as the working electrode is presented. A stop-start motion of the flow conditions in the intermittent cell is created using a piston pump, and this considerably increases the rate of electrochemical conversion of CO2 to HCOOH compared to a continuous flow system. The system works by stopping the flow of the electrolytes at a controlled frequency, which allows for sufficient time for more CO2 anion radicals (intermediate species) to be reduced into HCOOH instead of being washed away from the surface of the electrode. The findings presented here provide an important basis from which the design of CO2 reduction systems for industrial-scale applications can be started.

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Fabrication and electrochemical properties of boron-doped SiC

Uchiyama K., Yamamoto T., Einaga Y.

Carbon (Carbon) 174 240 - 247 2021.04

ISSN 00086223

Silicon carbide (SiC) has excellent properties such as chemical and physical stability, biocompatibility, and high thermal conductivity. However, electrical conductivity of SiC is not high enough for electrochemical applications, which has been a major challenge. Here, in order to improve the conductivity, we prepared boron-doped SiC (SiC:B) and evaluated the electrochemical properties. SiC and SiC:B were fabricated by a microwave plasma chemical vapor deposition method. Structural characterization revealed that the main phase of SiC:B is 3C–SiC where the concentration of doped boron could be controlled by tuning the growth conditions. Electrochemical properties were evaluated by cyclic voltammetry measurements, indicating that the reactivity and sensitivity of the SiC:B electrode was comparable of that of the glassy carbon electrode.

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Annealing enhancement in stability and performance of copper modified boron-doped diamond (Cu-BDD) electrode for electrochemical nitrate reduction

Kuang P., Natsui K., Einaga Y., Feng C., Cui Y., Zhang W., Deng Y.

Diamond and Related Materials (Diamond and Related Materials) 114 2021.04

ISSN 09259635

Nitrate contamination in groundwater requires efficient remediation to prevent adverse environmental impacts. This study illustrates the improvement in nitrate reduction process using copper modified BDD (Cu-BDD) with higher stability after annealing treatment. The highest values for nitrate reduction and the selectivity of nitrogen gas were about 71% and 45%, respectively, which were obtained using annealed Cu-BDD electrode. Annealing process promoted the homogeneity of copper oxides that consolidated the electrodeposited copper oxides on the surface of Cu-BDD to enhance the stability of electrode. Meanwhile, annealed Cu-BDD exhibited higher conductivity to facilitate nitrate reduction initiating at a more positive potential. Furthermore, cuprous ions and metallic Cu were formed during the annealing treatment, and had active chemical reaction with nitrate and excellent catalytic capability for the reaction, which efficiently enhanced either the nitrate reduction efficiency or the selectivity of nitrogen gas. The findings advance the current understanding on the enhancement of electrochemical stability and nitrate reduction performance using Cu-BDD after the annealing treatment, and also offer a promising technology for remediation of nitrate-contaminated groundwater.

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Nickel hydroxide nanoparticles for application in immunochromatographic strip tests of melamine

Saepudin E., Yuliani T., Musyarofah N.R.R., Nasution M.A.F., Gunlazuardi J., Einaga Y., Ivandini T.A.

Sensors and Materials (Sensors and Materials) 33 ( 3-2 ) 1027 - 1036 2021.03

ISSN 09144935

Nickel hydroxide nanoparticles [Ni(OH)2-NPs] synthesized by a complexation-precipitation method under hydrothermal conditions were employed as a probe in immunochromatographic strip tests for the selective detection of melamine. The characterization of Ni(OH) -NPs and their conjugation to anti-melamine antibody (anti-MEL) were performed using a UV- visible spectrophotometer, Fourier transform infrared (FTIR) spectroscopy, and TEM. On the basis of the green line intensity, the strip test can selectively detect melamine at a minimum concentration of 25 ppm. Our results suggest that this system is promising for the quantitative detection of melamine. 2

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Nanodiamonds Inhibit Cancer Cell Migration by Strengthening Cell Adhesion: Implications for Cancer Treatment

Guo Q., Li L., Gao G., Liu R., Einaga Y., Zhi J.

ACS Applied Materials and Interfaces (ACS Applied Materials and Interfaces) 13 ( 8 ) 9620 - 9629 2021.03

ISSN 19448244

Nanodiamonds (NDs) are a type of biocompatible nanomaterial with easily modified surfaces and are considered as promising candidates in biomedicine. In this work, the inhibition of tumor cell migration by carboxylated nanodiamonds (cNDs) was investigated. AFM-based single cell adhesion and F-actin staining experiments demonstrated that cNDs treatment could enhance cell adhesion and impair assembly of the cytoskeleton. The mechanism analysis of the regulatory protein expression level also proved that cNDs could inhibit the migration of Hela cells by preventing the epithelial-mesenchymal transition (EMT) process through the transforming growth factor β (TGF-β) signaling pathway. The in vivo pulmonary metastasis model also showed that cNDs effectively reduced the metastasis of murine B16 melanoma cells. In summary, cNDs have been demonstrated to inhibit cancer cell migration in vitro and decrease tumor metastasis in vivo. Therefore, cNDs might have potential utility for specific cancer treatment.

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Electrogenerated Chemiluminescence of Luminol Mediated by Carbonate Electrochemical Oxidation at a Boron-Doped Diamond

Irkham , Rais R.R., Ivandini T.A., Fiorani A., Einaga Y.

Analytical Chemistry (Analytical Chemistry) 93 ( 4 ) 2336 - 2341 2021.02

ISSN 00032700

The electrogenerated chemiluminescence of luminol is a process by which light generation is triggered by adding hydrogen peroxide and then applying a suitable electrode potential. Here, we take this phenomenon one step forward by avoiding the addition of hydrogen peroxide using a smart combination of a boron-doped diamond electrode and a carbonate electrolyte to generate the hydrogen peroxide directly in situ. The reaction occurs because of the carbonate electrochemical oxidation to peroxydicarbonate and the following hydrolysis to hydrogen peroxide, which triggers the emission from luminol. The electrogenerated chemiluminescence emission has been optimized by an investigation of the applied potentials, the carbonate concentration, and the pH. Furthermore, these results have been used to shine a light on the reaction mechanisms. Because this method does not require the addition of hydrogen peroxide, it might find application in efforts to avoid instability of hydrogen peroxide or its interference with the analytes of interest.

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Recent progress in direct urea fuel cell

Putri Y.M.T.A., Gunlazuardi J., Yulizar Y., Wibowo R., Einaga Y., Ivandini T.A.

Open Chemistry (Open Chemistry) 19 ( 1 ) 1116 - 1133 2021.01

Direct urea fuel cell (DUFC) has attracted many researchers' attention due to the use of wastewater, for example urine, which contains urea for the fuel. The main factor to improve the electrochemical oxidation performance of urea and further enhance the performances of DUFC is the use of a good anode catalyst. Non-noble metal catalyst, such as nickel, is reported to have a good catalytic activity in alkaline medium towards urea electro-oxidation. Besides optimizing the anode catalyst, the use of supporting electrode which has a large surface area as well as the use of H2O2 as an oxidant to replace O2 could help to improve the performances. The recent progress in anode catalysts for DUFC is overviewed in this article. In addition, the advantages and disadvantages as well as the factors that could help to escalate the performance of DUFC are discussed together with the challenges and future perspectives.

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In situ infrared spectroscopy of dopamine oxidation/reduction reactions on a polycrystalline boron-doped diamond electrode

Hosoda R., Kamoshida N., Hoshi N., Einaga Y., Nakamura M.

Carbon (Carbon) 171 814 - 818 2021.01

ISSN 00086223

The oxidation of dopamine (DA) on a boron-doped diamond (BDD) electrode was investigated using in situ attenuated total reflection infrared spectroscopy (ATR-IR) and infrared reflection absorption spectroscopy (IRAS). Voltammogram showed multiple anodic/cathodic peaks for the oxidation/reduction of DA and its oxidized derivatives on the BDD electrode. The oxidation/reduction species on the surface and in solution were assigned using ATR-IR and IRAS, respectively. The anodic oxidation of DA promoted polymerization, and the polymerized DA (PDA) was continuously deposited on BDD without being reduced by potential cycles, which resulted in the irreversible behavior of the voltammogram. A decrease in the oxidation current of DA by potential cycles was due to the deposition of PDA. Some intermediate quinone species, such as dopaminequinone and dopaminechrome, were reversibly reduced to hydroquinone.

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Nanoscale Reactivity Mapping of a Single-Crystal Boron-Doped Diamond Particle

Ando T., Asai K., MacPherson J., Einaga Y., Fukuma T., Takahashi Y.

Analytical Chemistry (Analytical Chemistry) 93 ( 14 ) 5831 - 5838 2021

ISSN 00032700

Boron-doped diamond (BDD) is most often grown by chemical vapor deposition (CVD) in polycrystalline form, where the electrochemical response is averaged over the whole surface. Deconvoluting the impact of crystal orientation, surface termination, and boron-doped concentration on the electrochemical response is extremely challenging. To tackle this problem, we use CVD to grow isolated single-crystal microparticles of BDD with the crystal facets (100, square-shaped) and (111, triangle-shaped) exposed and combine with hopping mode scanning electrochemical cell microscopy (HM-SECCM) for electrochemical interrogation of the individual crystal faces (planar and nonplanar). Measurements are made on both hydrogen- (H-) and oxygen (O-)-terminated single-crystal facets with two different redox mediators, [Ru(NH3)6]3+/2+ and Fe(CN)64-/3-. Extraction of the half-wave potential from linear sweep and cyclic voltammetric experiments at all measurement (pixel) points shows unequivocally that electron transfer is faster at the H-terminated (111) surface than at the H-terminated (100) face, attributed to boron dopant differences. The most dramatic differences were seen for [Ru(NH3)6]3+/2+ when comparing the O-terminated (100) surface to the H-terminated (100) face. Removal of the H-surface conductivity layer and a potential-dependent density of states were thought to be responsible for the behavior observed. Finally, a bimodal distribution in the electrochemical activity on the as-grown H-terminated polycrystalline BDD electrode is attributed to the dominance of differently doped (100) and (111) facets in the material.

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Anodic Oxidation of Phenols: A Key Step for the Synthesis of Natural Products

Yamamoto T., Saitoh T., Einaga Y., Nishiyama S.

Chemical Record (Chemical Record) 21 ( 9 ) 2254 - 2268 2021

ISSN 15278999

Natural products have played a significant role not only in discovery of drugs but also in development of organic chemistry by providing the synthetic challenges. Inspired by biosynthesis where enzymes catalyze a multi-step reaction, we have investigated the natural product synthesis utilizing electrochemical reactions as the key step. Electrochemical organic synthesis, so-called electro-organic synthesis, enables to control the reactivity of substrates simply by tuning electrolysis conditions. In this Personal Account, we overview the recent progress of our research projects about natural product synthesis, in which anodic oxidation of phenol compounds affords the important frameworks such as diaryl ether, spirodienone, and spiroisoxazoline.

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Electrochemical Sensing Applications Using Diamond Microelectrodes

Ivandini T.A., Einaga Y.

Bulletin of the Chemical Society of Japan (Bulletin of the Chemical Society of Japan) 94 ( 12 ) 2838 - 2847 2021

ISSN 00092673

The miniaturization of boron-doped diamond (BDD) electrodes is an important requirement for application to the study of electrochemical processes in living beings. In this work, we describe the fabrication and characterization of BDD electrodes with micrometer dimensions, with a particular emphasis on micro needle electrodes. As a result of the combination of the microelectrode size effect and the intrinsic properties of the diamond films, these electrodes showed not only a significantly lower background current than diamond macroelectrodes, but also an ability for use in analytical sensing in low conductive media. Accordingly, a wider range of experiments including in vivo measurements could be performed.

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Micro-band Boron-doped Diamond Electrode in Capillary Electrophoresis for Simultaneous Detection of AMP, ADP, and ATP

Prayikaputri P.U., Jiwanti P.K., Nasution M.A.F., Gunlazuardi J., Saepudin E., Einaga Y., Ivandini T.A.

International Journal of Technology (International Journal of Technology) 12 ( 2 ) 252 - 262 2021

ISSN 20869614

A micro-band boron-doped diamond (BDD) electrode was prepared by sealing a piece of BDD film with an area of 1.11×10-7 m2 between two insulating plates, one Teflon and one silicon rubber, to form sandwich-like layers, so the surface area could be investigated. The micro-band BDD was combined with capillary zone electrophoresis as an electrode for the simultaneous detection of adenosine monophosphate (AMP), adenosine diphosphate (ADP), and adenosine triphosphate (ATP) in a solution. These adenosine phosphates can be separated with a 0.3 m-long fused silica capillary using Britton–Robinson buffers at pH 2.0. Current in the concentration range of 0.1 to 2.0 mM were linear with the limits of detection of 0.004 μM, 0.006 μM, and 0.011 μM for AMP, ADP, and ATP, respectively. A comparison with an unmodified BDD as the detector in the same electrophoresis system showed that the micro-band generated better limits of detection (LODs) than the macroelectrode. This method was successfully applied to human urine samples injected with three adenosine phosphates, as well as adenine and guanine, which can be well-separated with recovery percentages of adenine, guanine, AMP, ADP, and ATP of 99.2%, 102.5%, 107.4%, 107.7%, and 105.4%, respectively.

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Electrogenerated Chemiluminescence for Immunoassay Applications

Rahmawati I., Irkham I., Wibowo R., Gunlazuardi J., Einaga Y., Ivandini T.A.

Indonesian Journal of Chemistry (Indonesian Journal of Chemistry) 21 ( 6 ) 1599 - 1618 2021

ISSN 14119420

Electrogenerated chemiluminescence (ECL) has recently become one of the most prominent and well-established transducers for immunoassay techniques. ECL relates a luminophore concentration in solution with the emission of light triggered by an electrochemical stimulus. ECL immunoassay (ECLIA) performance depends on the parameters of its light generation, including the luminophore, the species that emit light called labels in ECLIA; co-reactants, which are added reagents that support the luminophore to undergo the excited state; electrodes, which are the place for the ECL reactions to take place; and the format of the immunoassay. This review discusses the behaviour of ECLIA parameters, the required instrumentations, and some important examples of detections based on ECLIA.

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Study of carbon dioxide electrochemical reduction in flow cell system using copper modified boron-doped diamond

Zahran Ilyasa S., Krisma Jiwanti P., Khalil M., Einaga Y., Anggraningrum Ivandini T.

E3S Web of Conferences (E3S Web of Conferences) 211 2020.11

ISSN 25550403

High concentrations of CO2 in the atmosphere may cause climate and environmental changes. Therefore, various research has been extensively performed to reduce CO2 by converting CO2 directly into hydrocarbons. In this research, CO2 electrochemical reduction was studied using boron-doped diamond (BDD) modified with copper nanoparticles to improve BDD electrodes' catalytic properties. The deposition was performed by chronoamperometry technique at a potential of -0.6 V (vs. Ag/AgCl) and characterized using SEM, EDS, XPS, and cyclic voltammetry (CV). CO2 electrochemical reduction on BDD and Cu-BDD was carried out at -1.5 V (vs. Ag/AgCl) for 60 minutes. The products were analyzed using HPLC and GC. The product was mainly formic acid with a concentration of 11.33 mg/L and 33% faradaic efficiency on a Cu-BDD electrode.

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In Vivo Real-Time Simultaneous Examination of Drug Kinetics at Two Separate Locations Using Boron-Doped Diamond Microelectrodes

Hanawa A., Ogata G., Sawamura S., Asai K., Kanzaki S., Hibino H., Einaga Y.

Analytical Chemistry (Analytical Chemistry) 92 ( 20 ) 13742 - 13749 2020.10

ISSN 00032700

Methylcobalamin, which is used for the clinical treatment of patients with neuropathy, can have an impact on the sensorineural components associated with the cochlea, and it is possible that the auditory threshold in a certain population of patients with deafness may be recovered. Nonetheless, it remains uncertain whether the action site of methylcobalamin is localized inside or outside the cochlea and which cellular or tissue element is targeted by the drug. In the present work, we developed a method to realize in vivo real-time simultaneous examination of the drug kinetics in two separate locations using boron-doped diamond microelectrodes. First, the analytical performance of methylcobalamin was studied and the measurement protocol was optimized in vitro. Then, the optimized protocol was applied to carry out real-time measurements inside the cochlea and the leg muscle in live guinea pigs while systemically administering methylcobalamin. The results showed that the methylcobalamin concentration in the cochlea was below the limit of detection for the microelectrodes or the drug did not reach the cochlea, whereas the compound clearly reached the leg muscle.

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Study of nitrate contaminants removal from groundwater on copper modified BDD electrode

Kuang P., Cui Y., Feng C., Einaga Y.

E3S Web of Conferences (E3S Web of Conferences) 194 2020.10

ISSN 25550403

The electrochemical nitrate reduction by using boron-doped diamond (BDD) and copper modified boron-doped diamond (Cu-BDD) electrodes was investigated at various potentials. Nitrate reduction efficiency and the products distribution was strongly dependent on the applied potential for both electrodes. The highest nitrate reduction efficiency of 77% was obtained at -2.0 V (vs. Ag/AgCl) by using Cu-BDD. Compared with BDD electrode, nitrate reduction on Cu-BDD electrode occurred at more positive potential. Copper oxides formed on BDD surface efficiently promoted enhanced conductivity of electrode to promote electrons transfer during nitrate reduction process. Meanwhile, the catalytic ability of copper was also conductive to the nitrate transformation. Therefore, the developed Cu-BDD would be a promising approach for efficient nitrate removal from groundwater.

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Oxidation reaction of dissolved hydrogen sulfide using boron doped diamond

Triana Y., Tomisaki M., Einaga Y.

Journal of Electroanalytical Chemistry (Journal of Electroanalytical Chemistry) 873 2020.09

ISSN 15726657

© 2020 Elsevier B.V. We studied an oxidation reaction of dissolved hydrogen sulfide using boron doped diamond (BDD) electrodes and 0.1 mol Lˉ1 KClO4 as an electrolyte. Oxidation of H2S and HSˉ started at potentials of +1.7 V and + 0.5 V (vs. Ag/AgCl), respectively. In order to study the oxidation behavior, the effects of pH and the scan rate were investigated. Moreover, as demonstrated by X-ray photoelectron spectroscopy, no sulfur fouling was detected on the BDD surface. A linear calibration curve was observed in the concentration range of 0.08–2.34 mg Lˉ1 (r2 = 0.99) with a detection limit of 0.82 μg Lˉ1 (S/N = 3). In addition, an interference test with CO2 was performed, which showed there was no significant interference to the sensor.

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Weak Antilocalization and Spin Hall Effect in Pt Films Doped with Molecular Spin

Iwamoto W., Yamamoto T., Tsuchii K., Tazaki Y., Asami A., Hayashi H., Einaga Y., Ando K.

ACS Applied Electronic Materials (ACS Applied Electronic Materials) 2 ( 7 ) 2098 - 2103 2020.07

© 2020 American Chemical Society. A high degree of tunability and versatility of organic chemistry has paved the way toward molecular engineering of electronic and spintronic devices. Here, we report molecular spin doping of a Pt film, the key material in spin orbitronics. The molecular spin doping using a monolayer of a metal terpyridine complex allows to control the interaction between the conduction electrons and localized magnetic moments in the Pt film. The interaction was probed by measuring the weak antilocalization, which demonstrates enhanced magnetic impurity scattering induced by the molecular spin doping. By measuring the spin-orbit torque generated by Pt doped with molecular spins, we found that the spin Hall effect is robust against the magnetic impurity scattering, showing that the significant spin-orbit coupling dominates the charge-to-spin conversion in Pt. These results demonstrate that the molecular spin doping paves the way to explore spin-orbitronics phenomena.

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Quantification of electrogenerated chemiluminescence from tris(bipyridine)ruthenium(ii) and hydroxyl ions

Fiorani A., Valenti G., Irkham , Paolucci F., Einaga Y.

Physical Chemistry Chemical Physics (Physical Chemistry Chemical Physics) 22 ( 27 ) 15413 - 15417 2020.07

ISSN 14639076

© 2020 the Owner Societies. In this work, we quantify the electrogenerated chemiluminescence arising from the reaction of electrogenerated tris(bipyridine)ruthenium(iii) with hydroxyl ions, in terms of emission intensity and reaction rate. Different electrode materials (glassy carbon and boron-doped diamond) and different supporting electrolytes (perchlorate, phosphate, and carbonate) were investigated with pH variation. Relative quantification of the electrogenerated chemiluminescence was achieved using the Ru(bpy)32+/tri-n-propylamine system, taken as a reference, with relative emission as low as 600 and 230 times that observed at the same coreactant concentration and the same pH, respectively. The kinetics was investigated by foot of the wave analysis of cyclic voltammetry to measure the turnover frequency of the reaction. This journal is

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Electrochemical reduction of nitrate on boron-doped diamond electrodes: Effects of surface termination and boron-doping level

Kuang P., Natsui K., Feng C., Einaga Y.

Chemosphere (Chemosphere) 251 2020.07

ISSN 00456535

© 2020 Elsevier Ltd This study is among the first to systematically study the electrochemical reduction of nitrate on boron-doped diamond (BDD) films with different surface terminations and boron-doping levels. The highest nitrate reduction efficiency was 48% and the highest selectivity in the production of nitrogen gas was 44.5%, which were achieved using a BDD electrode with a hydrogen-terminated surface and a B/C ratio of 1.0%. C–H bonds served as the anchor points for attracting NO3− anions close to the electrode surface, and thus accelerating the formation of NO3−(ads). Compared to oxygen termination, hydrogen-terminated BDD exhibited higher electrochemical reactivity for reducing nitrate, resulting from the formation of shallow acceptor states and small interfacial band bending. The hydrophobicity of the hydrogen-terminated BDD inhibited water electrolysis and the subsequent adsorption of atomic hydrogen, leading to increased selectivity in the production of nitrogen gas. A BDD electrode with a boron-doping level of 1.0% increased the density of acceptor states, thereby enhancing the conductivity and promoting the formation of C–H bonds after the cathodic reduction pretreatment leading to the direct reduction of nitrate.

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Effect of sp2 species in a boron-doped diamond electrode on the electrochemical reduction of CO<inf>2</inf>

Xu J., Einaga Y.

Electrochemistry Communications (Electrochemistry Communications) 115 2020.06

ISSN 13882481

© 2020 The Authors The effect of sp2 carbon within a boron-doped diamond (BDD) electrode on the electrochemical reduction of CO2 is investigated for the first time. With increasing sp2 content, the Faradaic efficiency for the production of hydrogen (H2) under constant current density increases while that for the production of formic acid (HCOOH) decreases. Moreover, favorable electrolysis conditions for producing HCOOH shift in the negative potential direction with increasing sp2 content. This phenomenon is ascribed to the presence of adsorption sites on the sp2 carbon. This work provides guidance for selectively controlling the reduction of CO2 by adjusting the distribution of carbonaceous species in the BDD electrode.

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Improving the CO<inf>2</inf> electrochemical reduction to formic acid using iridium-oxide-modified boron-doped diamond electrodes

Jiwanti P.K., Ichzan A.M., Dewandaru R.K.P., Atriardi S.R., Einaga Y., Ivandini T.A.

Diamond and Related Materials (Diamond and Related Materials) 106 2020.06

ISSN 09259635

© 2020 Elsevier B.V. Modification of iridium on the surface of boron-doped diamond (BDD) electrode has been performed to decrease the overpotential reduction of carbon dioxide (CO2) and produce value-added carbon compounds. The modification was performed using the cyclic voltammetry (CV) technique that successfully deposited iridium oxide on the surface of the BDD electrode with an Ir-to-C ratio of approximately 1:100. When the modified BDD electrode was utilized for CV of a dissolved-CO2-saturated solution, hydrogen evolution occurred at a potential of approximately −1.2 V (vs. Ag/AgCl), which was lower than that when an unmodified BDD was used. Furthermore, when this electrode was utilized for amperometry of the same solution at −1.7 V for 1 h, formic acid (HCOOH) was produced with a Faradaic efficiency of approximately 50%. Results indicated that the modified electrode has considerable potential for application to CO2 electrochemical reduction.

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Enhancement of coercivity of self-assembled stacking of ferrimagnetic and antiferromagnetic nanocubes

Sawano K., Tsukiyama K., Shimizu M., Takasaki M., Oaki Y., Yamamoto T., Einaga Y., Jenewein C., Cölfen H., Kaiju H., Sato T., Imai H.

Nanoscale (Nanoscale) 12 ( 14 ) 7792 - 7796 2020.04

ISSN 20403364

© The Royal Society of Chemistry . The coercivity of magnetic nanoparticles is enhanced by the exchange coupling effect at the interface of ferrimagnetic and antiferromagnetic self-assembled monolayers. Antiferromagnetic Co3O4 nanocubes were regularly stacked on an ordered monolayer of ferrimagnetic Fe3O4 nanocubes by layer-by-layer manipulation using evaporation-driven self-assembly. The ordered arrangements of the ferrimagnetic and antiferromagnetic nanocubes are effective for the enhancement of the ferromagnetic character.

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Stable iridium-modified boron-doped diamond electrode for the application in electrochemical detection of arsenic (III)

Agustiany T., Khalil M., Einaga Y., Jiwanti P., Ivandini T.

Materials Chemistry and Physics (Materials Chemistry and Physics) 244 2020.04

ISSN 02540584

© 2020 Elsevier B.V. Preparation of stable iridium-modified boron-doped diamond electrodes through electrodeposition was studied. The electrode was prepared by wet chemical seeding and thermal annealing that performed before and after the electrodeposition process in order to get a homogeneous deposition. The modified electrode from each step was characterized using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Raman and X-Ray photoelectron spectroscopy (XPS) to understand the surface topography and its elemental composition. In addition, cyclic voltammetry for arsenic (III) was performed to examine the electrochemical behavior of the modified diamond. At an optimum condition in a phosphate buffer solution pH 3 and a scan rate of 50 mV/s, a linear calibration curve in the concentration range of 1–100 μM with a detection limit of 4.64 μM was achieved. Excellent stability and repeatability were also observed with relative standard deviations of 2.6% and <0.4%, respectively. Additionally, the electrode exhibited good linearity and sensitivity towards the measurement of arsenic (III) in both arsenic (III)-added tap water and lake water samples.

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Avian Influenza Virus Detection by Optimized Peptide Termination on a Boron-Doped Diamond Electrode

Matsubara T., Ujie M., Yamamoto T., Einaga Y., Daidoji T., Nakaya T., Sato T.

ACS Sensors (ACS Sensors) 5 ( 2 ) 431 - 439 2020.02

Copyright © 2020 American Chemical Society. The development of a simple detection method with high sensitivity is essential for the diagnosis and surveillance of infectious diseases. Previously, we constructed a sensitive biosensor for the detection of pathological human influenza viruses using a boron-doped diamond electrode terminated with a sialyloligosaccharide receptor-mimic peptide that could bind to hemagglutinins involved in viral infection. Circulation of influenza induced by the avian virus in humans has become a major public health concern, and methods for the detection of avian viruses are urgently needed. Here, peptide density and dendrimer generation terminated on the electrode altered the efficiency of viral binding to the electrode surface, thus significantly enhancing charge-transfer resistance measured by electrochemical impedance spectroscopy. The peptide-terminated electrodes exhibited an excellent detection limit of less than one plaque-forming unit of seasonal H1N1 and H3N2 viruses. Furthermore, the improved electrode was detectable for avian viruses isolated from H5N3, H7N1, and H9N2, showing the potential for the detection of all subtypes of influenza A virus, including new subtypes. The peptide-based electrochemical architecture provided a promising approach to biosensors for ultrasensitive detection of pathogenic microorganisms.

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Microfluidic screening system based on boron-doped diamond electrodes and dielectrophoretic sorting for directed evolution of NAD(P)-dependent oxidoreductases

Goto H., Kanai Y., Yotsui A., Shimokihara S., Shitara S., Oyobiki R., Fujiwara K., Watanabe T., Einaga Y., Matsumoto Y., Miki N., Doi N.

Lab on a Chip (Lab on a Chip) 20 ( 4 ) 852 - 861 2020.02

ISSN 14730197

This journal is © The Royal Society of Chemistry. We report the development of a micro total analysis system (μTAS) based on electrochemical measurements and dielectrophoretic sorting for screening of NAD(P)-dependent oxidoreductases. In this system, the activity of enzymes immobilized on microbeads, together with their encoding DNA, can be measured with a boron-doped diamond (BDD) electrode in each compartment (∼30 nL) of the microfluidic system. The 30 nL droplets containing microbead-displayed genes of enzymes with higher activity can then be recovered by dielectrophoretic sorting. Previously, we developed the NAD(P)H-measuring device containing the BDD electrode for high-throughput measurement of the activity of NAD(P)-dependent oxidoreductases. In this study, we fabricated an encapsulating device and a droplet-sorting device for nanoliter-size droplets, for the first time, and then combined these three devices to construct a μTAS for directed evolution of NAD(P)-dependent oxidoreductases. We confirmed that this system works by proof-of-principle experiments and successfully applied this system for screening of randomized libraries of NAD-dependent dehydrogenases.

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Unusual Electrochemical Properties of Low-Doped Boron-Doped Diamond Electrodes Containing sp2 Carbon

Xu J., Yokota Y., Wong R.A., Kim Y., Einaga Y.

Journal of the American Chemical Society (Journal of the American Chemical Society) 142 ( 5 ) 2310 - 2316 2020.02

ISSN 00027863

Copyright © 2020 American Chemical Society. Unexpected phenomena displayed by low-boron-doped diamond (BDD) electrodes are disclosed in the present work. Generally, the presence of sp2 nondiamond carbon impurities in BDD electrodes causes undesirable electrochemical properties, such as a reduced potential window and increased background current, etc. However, we found that the potential window and redox reaction in normally doped (1%) BDD and low-doped (0.1%) BDD exhibited opposite tendencies depending on the extent of sp2 carbon. Moreover, we found that contrary to the usual expectations, low-doped BDD containing sp2 carbon hinders electron transfer, whereas in line with expectations, normally doped BDD containing sp2 exhibits enhanced electron transfer. Surface analyses by X-ray/ultraviolet photoelectron spectroscopy (XPS/UPS) and electrochemical methods are utilized to explain these unusual phenomena. This work indicates that the electrochemical properties of low-doped BDD containing sp2 might be due partially to the high level of surface oxygen, the large work function, the low carrier density, and the existence of different types of sp2 carbon.

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Electrogenerated Chemiluminescence by in Situ Production of Coreactant Hydrogen Peroxide in Carbonate Aqueous Solution at a Boron-Doped Diamond Electrode

Irkham , Fiorani A., Valenti G., Kamoshida N., Paolucci F., Einaga Y.

Journal of the American Chemical Society (Journal of the American Chemical Society) 142 ( 3 ) 1518 - 1525 2020.01

ISSN 00027863

© 2019 American Chemical Society. An electrogenerated chemiluminescence (ECL) system by in situ coreactant production, where Ru(bpy)32+ emission is generated at a boron-doped diamond (BDD) electrode, is presented. The system takes advantage of the unique properties of BDD to promote oxidation of carbonate (CO32-) into peroxydicarbonate (C2O62-), which further reacts with water to form hydrogen peroxide (H2O2), which acts as a coreactant for Ru(bpy)32+ ECL. Investigation of the mechanism reveals that ECL emission is triggered by the reduction of H2O2 to hydroxyl radicals (OH•), which later react with the reduced Ru(bpy)3+ molecules to form excited states, followed by light emission. The ECL signal was found to increase with the concentration of CO32- therefore, with the concentration of electrogenerated H2O2, although at the same time, higher concentrations of H2O2 can quench the ECL emission, resulting in a decrease in intensity. The carbonate concentration, pH, and oxidation parameters, such as potential and time, were optimized to find the best emission conditions.

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An electrochemical aptamer-based sensor prepared by utilizing the strong interaction between a DNA aptamer and diamond

Asai K., Yamamoto T., Nagashima S., Ogata G., Hibino H., Einaga Y.

Analyst (Analyst) 145 ( 2 ) 544 - 549 2020.01

ISSN 00032654

© 2020 The Royal Society of Chemistry. Stable and continuous biosensing of electroactive species in vivo has been achieved by using boron-doped diamond (BDD) electrodes owing to their outstanding electrochemical properties. However, the present problem in biosensing using BDD electrodes is how to specifically measure/detect the target molecules, including electrochemically inactive species. A possible solution is to fabricate an electrochemical aptamer-based (E-AB) sensor using a BDD electrode. In a preliminary investigation, we found that DNA aptamers strongly adsorb on the BDD surface and the aptamer-adsorbed BDD apparently worked as an E-AB sensor. The present study reports the performance of the aptamer-adsorbed BDD electrode as an E-AB sensor. Doxorubicin (DOX), a widely used chemotherapeutic, was chosen as a target molecule. The sensor could be prepared by just dipping BDD in an aptamer solution for only 30 min, and the electrochemical signals were dependent on the DOX concentration. The adsorption of DNA was strong enough for continuous measurements and even a sonication treatment. Such behaviors were not observed when using gold and glassy carbon electrodes. In a kinetic measurement, distortion by a sluggish response was observed for both association and dissociation phases, indicating that the interaction between DOX and the aptamer involves several kinetic processes. By fitting to a Langmuir isotherm, a limit of detection of 49 nM and a maximum detectable concentration of 2.3 μM were obtained. Although the sensitivity was lower than those of the well-established E-AB sensors of gold, the values are within a drug's therapeutic range. Overall, the present work demonstrates that a DNA aptamer and a BDD electrode is an effective combination for an E-AB sensor with stable sensitivity, and a wide variety of DNA aptamers can be applied without any special treatment.

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Electrochemical Measurement of Bismuth Clusters in Dendrimer Through Transformation from Atomicity Controlled Complexes

Kambe T., Imaoka S., Hasegawa R., Tsukamoto T., Imaoka T., Natsui K., Einaga Y., Yamamoto K.

Journal of Inorganic and Organometallic Polymers and Materials (Journal of Inorganic and Organometallic Polymers and Materials) 30 ( 1 ) 169 - 173 2020.01

ISSN 15741443

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. Dendrimers can provide unique reaction space for sub-nano sized materials. Recently, we have demonstrated a luminous bismuth dendrimer and the on/off switching by stepwisely assembled bismuth units in a phenylazomethine dendrimers. In addition, formation of bismuth clusters was also demonstrated by the reduction of the bismuth salts assembled in the dendrimer. In this study, we have revealed the atomicity dependency about the reduction and oxidation potentials of the assembled bismuth complexes and clusters, respectively. The measurements were conducted by the electrochemical process of the bismuth assembled dendritic poly-phenylazomethines.

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Dielectrophoretic sorting system for screening of NAD(P)-dependent oxidoreductases.

Kanai Y., Shimokihara S., Shitara S., Oyobiki R., Watanabe T., Einaga Y., Wakamatsu K., Matsumoto Y., Fujiwara K., Doi N.

21st International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2017 (21st International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2017) 1383 - 1384 2020

ISSN 9780692941836

© 17CBMS-0001. Here we report the development of a flow injection analysis system based on electrochemical measurements and dielectrophoresis for screening of NAD(P)-dependent oxidoreductases. In this system, the activity of enzyme which is immobilized on microbeads together with its encoding DNA can be measured with a boron-doped diamond (BDD) electrode in each compartment (~30 nL) of the microfluidic system, and the large droplets (~30 nL) containing genes of enzymes with higher activity can be recovered by dielectrophoretic sorting.

Further study of CO<inf>2</inf> electrochemical reduction on palladium modified bdd electrode: Influence of electrolyte

Jiwanti P.K., Einaga Y.

Chemistry - An Asian Journal (Chemistry - An Asian Journal) 15 ( 6 ) 910 - 914 2020

ISSN 18614728

© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. The study of CO2 electrochemical reduction to useful compounds using bare or modified BDD electrode attracts numerous attentions. Meanwhile, the efficiency of products obtained from CO2 electrochemical reduction is known to be determined by the electrode material and the electrolyte. Formic acid as main product and CO as a minor product, have also been known on the CO2 reduction using BDD electrode. Recently, we reported the successful improvement of CO production from the reduction of CO2 by decorating the surface of BDD electrode with palladium particles. Following this, herein, we present further inves-tigation on electrolyte dependence, including cation and anion dependence and also concentration effect in order to understand deeply the CO2 reduction on surface of palladium modified BDD electrode. The results suggest the use of NaCl and KCl as a catholyte for optimum performance, in addition to the improvement of CO2 reduction product in higher electrolyte concentration.

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Preparation of boron-doped diamond modified by bimetal nickel and zinc

Putri Y.M.T.A., Jiwanti P.K., Irkham , Gunlazuardi J., Einaga Y., Ivandini T.A.

IOP Conference Series: Materials Science and Engineering (IOP Conference Series: Materials Science and Engineering) 902 ( 1 ) 2020

ISSN 17578981

Nickel has been known as a good catalyst due to its high activity and stability, but the potential formation of NiOOH is quite high. In this work, zinc together with nickel was used to modify the surface of boron-doped diamond (BDD) to lower the formation potential of NiOOH. Electro-deposition (multi pulse amperometry) technique was applied at a potential of -1.6 V for 600 s. The prepared electrode (NiZn-BDD) characterized using SEM-EDX and XPS shows that both nickel and zinc were deposited homogenously on the surface of BDD with the ratio of 1:2 for nickel:zinc.

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Diamond Electrodes for Electrogenerated Chemiluminescence

Fiorani A., Irkham1 , Valenti G., Einaga Y., Paolucci F.

Nanocarbon Electrochemistry (Nanocarbon Electrochemistry) 285 - 321 2019.11

ISSN 9781119468233

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Electrochemical oxidation of palmitic acid solution using boron-doped diamond electrodes

Muharam S., Jiwanti P., Irkham, Gunlazuardi J., Einaga Y., Ivandini T.

Diamond and Related Materials (Diamond and Related Materials) 99 2019.11

ISSN 09259635

© 2019 Elsevier B.V. Palmitic acid, a model compound for palm oil mill effluent (POME), was eliminated from a water–ethanol solution using electrochemical oxidation with a boron-doped diamond (BDD) electrode. For a palmitic acid solution in a water–ethanol solution, chronoamperometry with a potential of +3.0 V (vs Ag/AgCl) showed a decrease in chemical oxygen demand (COD) of ~85.75% in 4 h, whereas at a higher potential (+10.0 V), the COD decreased to 75.76% in 1 h. It was noticed that the use of high potentials for up to 4 h caused the structure damaged of the BDD.

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Observation of Proton Transfer Coupled Spin Transition and Trapping of Photoinduced Metastable Proton Transfer State in an Fe(II) Complex

Nakanishi T., Hori Y., Sato H., Wu S., Okazawa A., Kojima N., Yamamoto T., Einaga Y., Hayami S., Horie Y., Okajima H., Sakamoto A., Shiota Y., Yoshizawa K., Sato O.

Journal of the American Chemical Society (Journal of the American Chemical Society) 141 ( 36 ) 14384 - 14393 2019.09

ISSN 00027863

Copyright © 2019 American Chemical Society. An important technique to realize novel electron- A nd/or proton-based functionalities is to use a proton-electron coupling mechanism. When either a proton or electron is excited, the other one is modulated, producing synergistic functions. However, although compounds with proton-coupled electron transfer have been synthesized, crystalline molecular compounds that exhibit proton-transfer-coupled spin-transition (PCST) behavior have not been reported. Here, we report the first example of a PCST Fe(II) complex, wherein the proton lies on the N of hydrazone and pyridine moieties in the ligand at high-spin and low-spin Fe(II), respectively. When the Fe(II) complex is irradiated with light, intramolecular proton transfer occurs from pyridine to hydrazone in conjunction with the photoinduced spin transition via the PCST mechanism. Because the light-induced excited high-spin state is trapped at low temperatures in the Fe(II) complex- A phenomenon known as the light-induced excited-spin-state trapping effect-the light-induced proton-transfer state, wherein the proton lies on the N of hydrazone, is also trapped as a metastable state. The proton transfer was accomplished within 50 ps at 190 K. The bistable nature of the proton position, where the position can be switched by light irradiation, is useful for modulating proton-based functionalities in molecular devices.

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Oxidation of hydroxide ions in weak basic solutions using boron-doped diamond electrodes: Effect of the buffer capacity

Irkham , Einaga Y.

Analyst (Analyst) 144 ( 15 ) 4499 - 4504 2019.08

ISSN 00032654

© 2019 The Royal Society of Chemistry. The electrochemical oxidation of hydroxide ions using boron-doped diamond (BDD) electrodes in weak basic solutions was examined. Using simple linear sweep voltammetry (LSV), a well-shaped peak originating from the oxidation of hydroxide ions involving a CE mechanism was observed at ∼1.30 V versus a Ag/AgCl reference electrode in 20 mM H3PO4 solutions with hydroxide ion concentrations ranging from 0.1 to 10 mM. Compared to a NaOH solution with the same hydroxide ion concentration, the peak current in the phosphate solution was found to be higher due to the buffering capability of the phosphate solution, which maintains the hydroxide ion concentration, making it possible to provide more hydroxide ions to the surface of the electrode. The peak was found to depend not only on the hydroxide ion concentration, but also on the phosphate concentration, confirming that the origin of the peak was due to oxidation of the hydroxide ions enhanced by the buffering capability of the weak basic solution. These results further promote the use of BDD electrodes for measuring hydroxide ion concentration, and offer the possibility of directly measuring the buffer capacity of a solution.

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Electrochemical mineralization of dimethyl sulfoxide on boron-doped diamond electrodes

Natsui K., Hosomi T., Ikemiya N., Einaga Y.

Environmental Technology and Innovation (Environmental Technology and Innovation) 15 2019.08

© 2019 Elsevier B.V. Dimethyl sulfoxide (DMSO) is an excellent organic solvent, and widely used in laboratories and industries. Therefore, plenty amount of wastewater containing DMSO have been discharged. As the DMSO is high resistant to biological process which is mostly used for wastewater treatments, other strong treatments are needed. Electrochemical oxidation using boron-doped diamond (BDD) anode is a promising method due to effective generation of free hydroxyl radicals which are quite strong oxidizing agents. In this work, a simulated wastewater containing DMSO was treated by the anodic oxidation using BDD electrodes. We found that BDD electrodes could oxidize and completely mineralize DMSO. Removal of total organic carbon was more than 99% after the electrolysis for 5 h using BDD electrodes. This is first observation for the electrochemical mineralization of persistent DMSO. Moreover, BDD electrodes enabled to mineralize DMSO without electrolytic corrosion at low current densities and high pH of the solution for the treatments.

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Influence of the Nature of Boron-Doped Diamond Anodes on the Dehydrogenative Phenol-Phenol Cross-Coupling

Gleede B., Yamamoto T., Nakahara K., Botz A., Graßl T., Neuber R., Matthée T., Einaga Y., Schuhmann W., Waldvogel S.

ChemElectroChem (ChemElectroChem) 6 ( 10 ) 2771 - 2776 2019.05

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Boron-doped diamond (BDD) represents a powerful and innovative electrode material. In particular, in combination with fluorinated solvents such as 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), the system exhibits the largest known electrochemical window of approximately 5 V in protic media. Furthermore, the anodic treatment allows the direct formation of oxyl radicals, which are known to exhibit specific reactivity. The electrochemical dehydrogenative phenol-phenol cross-coupling is a versatile and useful transformation to non-symmetric biphenols. This electro-organic conversion can be divided into two regimes: initial oxidation at the anode and the electrolyte-controlled follow-up reaction. This work intends to provide an answer about the influence of BDD electrodes on oxidation reactions in electrosynthesis. Depending on the electro-organic transformation, the support material of BDD, its boron content, and its fabrication method have a significant influence on the electrosynthetic efficiency.

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Thermoresponsive, Freezing-Resistant Smart Windows with Adjustable Transition Temperature Made from Hydroxypropyl Cellulose and Glycerol

Nakamura C., Yamamoto T., Manabe K., Nakamura T., Einaga Y., Shiratori S.

Industrial and Engineering Chemistry Research (Industrial and Engineering Chemistry Research) 58 ( 16 ) 6424 - 6428 2019.04

ISSN 08885885

© 2019 American Chemical Society. A thermoresponsive smart window that can switch its transmittance to control heating from sunlight is attracting great attention. Such windows made from a hydrogel of a thermoresponsive polymer such as poly(N-isopropylacrylamide) (PNIPAm) or hydroxypropyl cellulose (HPC) have been successful and can switch their transmittance at room temperature. However, such hydrogels occasionally freeze in cold places, degrading their transmittance. Thus, a thermoresponsive hydrogel that can be used in various geographical regions is desired. Here, we produced a thermoresponsive smart window with freezing resistance made from HPC and glycerol. We could adjust its switching temperature by simply changing the amount of added glycerol, letting us easily change it to room temperature for practical use. These smart windows show high cyclic performance, freezing resistance, and heat shielding, demonstrating great potential.

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In Situ Spectroscopic Study on the Surface Hydroxylation of Diamond Electrodes

Kasahara S., Ogose T., Ikemiya N., Yamamoto T., Natsui K., Yokota Y., Wong R., Iizuka S., Hoshi N., Tateyama Y., Kim Y., Nakamura M., Einaga Y.

Analytical Chemistry (Analytical Chemistry) 91 ( 8 ) 4980 - 4986 2019.04

ISSN 00032700

Copyright © 2019 American Chemical Society. Carbon-based materials are regarded as an environmentally benign alternative to the conventional metal electrode used in electrochemistry from the viewpoint of sustainable chemistry. Among various carbon electrode materials, boron-doped diamond (BDD) exhibits superior electrochemical properties. However, it is still uncertain how surface chemical species of BDD influence the electrochemical performance, because of the difficulty in characterizing the surface species. Here, we have developed in situ spectroscopic measurement systems on BDD electrodes, i.e., in situ attenuated total reflection infrared spectroscopy (ATR-IR) and electrochemical X-ray photoelectron spectroscopy (EC-XPS). ATR-IR studies at a controlled electrode potential confirmed selective surface hydroxylation. EC-XPS studies confirmed deprotonation of C-OH groups at the BDD/electrolyte interface. These findings should be important not only for better understanding of BDD's fundamentals but also for a variety of applications.

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Switchable Product Selectivity in the Electrochemical Reduction of Carbon Dioxide Using Boron-Doped Diamond Electrodes

Tomisaki M., Kasahara S., Natsui K., Ikemiya N., Einaga Y.

Journal of the American Chemical Society (Journal of the American Chemical Society) 141 ( 18 ) 7414 - 7420 2019.04

ISSN 00027863

© 2019 American Chemical Society. The main product obtained by electrochemical reduction of CO 2 depends on the electrode material, and in many cases the Faradaic efficiency for this is determined by the electrolyte. Only a few investigations in which attempts to produce different products from the same electrode material have been done so far. In this work, we focus on boron-doped diamond (BDD) electrodes with which plentiful amounts of formic acid and small amounts of carbon monoxide have been produced. By optimizing certain parameters and conditions used in the electrochemical process with BDD electrodes, such as the electrolyte, the boron concentration of the BDD electrode, and the applied potential, we were able to control the selectivity and efficiency with which carbon monoxide is produced. On one hand, with a BDD electrode with 1% boron used for the cathode and KClO 4 for the catholyte, the selectivity for producing carbon monoxide was high. On the other hand, with a BDD electrode with 0.1% boron used for the cathode and KCl for the catholyte, the production of formic acid was the most evident. In situ attenuated total reflectance-infrared (ATR-IR) measurements during electrolysis showed that CO 2·- intermediates were adsorbed on the BDD surface in the KClO 4 aqueous solution. Here, switchable product selectivity was achieved when reducing CO 2 using BDD electrodes.

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Influence of Surface Orientation on Electrochemical Properties of Boron-Doped Diamond

Ivandini T., Watanabe T., Matsui T., Ootani Y., Iizuka S., Toyoshima R., Kodama H., Kondoh H., Tateyama Y., Einaga Y.

Journal of Physical Chemistry C (Journal of Physical Chemistry C) 123 ( 9 ) 5336 - 5344 2019.03

ISSN 19327447

© 2019 American Chemical Society. To study the influence of crystal orientation on the electrochemical properties of boron-doped diamond (BDD), electrodes comprising (100) and (111) homoepitaxial single-crystal layers of BDD were investigated and these were compared with a thin polycrystalline BDD electrode. The BDD samples with similar amounts of boron of around 1020 cm-3 and resistivity of around 6 × 10-3 ? cm were prepared. Evaluation of the electrochemical reactivity of each of the samples with both H- and O-terminated surfaces showed that polycrystalline BDD was the most reactive, whereas the (111) samples proved to be more reactive than the (100) ones for single-crystal BDD. Moreover, considering the results of first-principles molecular dynamics simulations, it is proposed that surface transfer doping is the dominating factor for H-terminated surfaces, whereas the degree of band bending and the thickness of the space-charge layer are the dominating factors for O-terminated surfaces.

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In situ ATR-IR study of Fe(CN) <inf>6</inf>3− /Fe(CN) <inf>6</inf>4− redox system on boron-doped diamond electrode

Kamoshida N., Kasahara S., Ikemiya N., Hoshi N., Nakamura M., Einaga Y.

Diamond and Related Materials (Diamond and Related Materials) 93 50 - 53 2019.03

ISSN 09259635

© 2019 Hexacyanoferrate redox couple is extensively used as a benchmark to evaluate electrode activity in aqueous electrochemistry. Interestingly, boron-doped diamond (BDD) electrode shows surface-dependent behaviors: fast electron transfer rate on hydrogen terminated surface and slow rate on oxygen terminated surface. On the other hand, origin of the surface-dependent response still remains unclear. In this study, we spectroscopically investigated the determinants of electrochemical activity of this system using in situ ATR-IR technique. Our experiment revealed that adsorbed intermediate species of this redox system exist on the hydrogen terminated BDD. On the oxygen terminated BDD, the bands of adsorbed species were weakened, indicating that the oxygen functional groups specifically inhibited the adsorption of the intermediate species.

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Conductive diamond: Synthesis, properties, and electrochemical applications

Yang N., Yu S., MacPherson J., Einaga Y., Zhao H., Zhao G., Swain G., Jiang X.

Chemical Society Reviews (Chemical Society Reviews) 48 ( 1 ) 157 - 204 2019.01

ISSN 03060012

© 2019 The Royal Society of Chemistry. Conductive diamond possesses unique features as compared to other solid electrodes, such as a wide electrochemical potential window, a low and stable background current, relatively rapid rates of electron-transfer for soluble redox systems without conventional pretreatment, long-term responses, stability, biocompatibility, and a rich surface chemistry. Conductive diamond microcrystalline and nanocrystalline films, structures and particles have been prepared using a variety of approaches. Given these highly desirable attributes, conductive diamond has found extensive use as an enabling electrode across a variety of fields encompassing chemical and biochemical sensing, environmental degradation, electrosynthesis, electrocatalysis, and energy storage and conversion. This review provides an overview of the fundamental properties and highlights recent progress and achievements in the growth of boron-doped (metal-like) and nitrogen and phosphorus-doped (semi-conducting) diamond and hydrogen-terminated undoped diamond electrodes. Applications in electroanalysis, environmental degradation, electrosynthesis electrocatalysis, and electrochemical energy storage are also discussed. Diamond electrochemical devices utilizing micro-scale, ultramicro-scale, and nano-scale electrodes as well as their counterpart arrays are viewed. The challenges and future research directions of conductive diamond are discussed and outlined. This review will be important and informative for chemists, biochemists, physicists, materials scientists, and engineers engaged in the use of these novel forms of carbon.

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The Utilization of Boron-doped Diamond Electrodes for the Electrochemical Reduction of CO <inf>2</inf> : Toward the production compounds with a high number of carbon atoms

Jiwanti P., Natsui K., Einaga Y.

Electrochemistry (Electrochemistry) 87 ( 2 ) 109 - 113 2019

ISSN 13443542

© The Electrochemical Society of Japan, All rights reserved. The utilization of boron doped diamond (BDD) as an electrode material for the electrochemical reduction of CO 2 has been studied in recent decades. Its stability and ability to suppress hydrogen evolution makes it an attractive choice for the electrochemical reduction of CO 2 . It has been confirmed that, when using a bare BDD electrode, very high selectivity and productivity can be achieved in the production of formic acid. Moreover, by modifying the surface of a BDD electrode with copper (Cu) particles, we have been able to produce compounds with a high number of carbon atoms. In this article, we summarize the results of our work on the electrochemical reduction of CO 2 using BDD electrodes, with the specific aim of the producing compounds with a high number of carbon atoms.

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Modification of boron-doped diamond electrodes with platinum to increase the stability and sensitivity of haemoglobin-based acrylamide sensors

Wulandari R., Ivandini T., Irkham, Saepudin E., Einaga Y.

Sensors and Materials (Sensors and Materials) 31 ( 4 ) 1105 - 1117 2019

ISSN 09144935

© MYU K.K. Boron-doped diamond (BDD) electrodes modified with platinum and haemoglobin (Hb) have been prepared for application as stable and sensitive acrylamide biosensors. The Platinum-modified BDD (Pt-BDD) was prepared in several steps, including the wet chemical seeding of Pt particles, the electrochemical overgrowth of Pt seeds, thermal annealing at 700 °C under N 2 atmosphere, as well as refresh and activation steps of Pt-BDD by cyclic voltammetry (CV). The characterization of the prepared Pt-BDD using scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS) showed that the method can deposit Pt homogenously on the BDD surface with an average particle size of around 200 nm. The Raman results showed that the treatment steps during modification did not damage the sp 3 carbon in the BDD structure. After modification with Hb, the modified BDD was examined for acrylamide detection. CVs of Hb-Pt-modified BDD (Hb-Pt-BDD) in 0.2 M acetate buffer saline (ABS) (pH 4.8) containing acrylamide in the concentration range of 0.01 to 1 nM showed linear responses with a detection limit of 0.0085 nM and a quantification limit of 0.026 nM. The excellent stability of the prepared Pt-BDD was confirmed as it showed the reusability of Pt-BDD by removing the Hb adduct without removing Pt on the BDD surface.

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Increasing the electric double-layer capacitance in boron-doped diamond electrodes

Takagi K., Natsui K., Watanabe T., Einaga Y.

ChemElectroChem (ChemElectroChem) 6 ( 6 ) 1683 - 1687 2019

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Highly boron-doped diamond (BDD) electrodes containing sp 2 carbon impurities exhibit an increase in the electric doublelayer capacitance (C dl ) after anodic oxidation. Although it is known that the electrochemical properties of BDD electrodes are affected by several factors, including the boron concentration, the amount of sp 2 carbon impurity, and the surface termination and orientation, clarification of the mechanism for the increase in C dl needs to be done. To this end, we prepared several BDD samples under various conditions and the properties of these samples, including C dl , were systematically investigated. The mechanism for the increase in C dl in particular, including the effect of the surface termination, is discussed.

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High-temperature cooperative spin crossover transitions and single-crystal reflection spectra of [Fe III (qsal) <inf>2</inf> ](CH <inf>3</inf> OSO <inf>3</inf> ) and related compounds

Takahashi K., Yamamoto K., Yamamoto T., Einaga Y., Shiota Y., Yoshizawa K., Mori H.

Crystals (Crystals) 9 ( 2 ) 2019

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. New Fe(III) compounds from qsal ligand, [Fe(qsal) 2 ](CH 3 OSO 3 ) (1) and [Fe(qsal) 2 ](CH 3 SO 3 )·CH 3 OH (3), along with known compound, [Fe(qsal) 2 ](CF 3 SO 3 ) (2), were obtained as large well-shaped crystals (Hqsal = N-(8-quinolyl)salicylaldimine). The compounds 1 and 2 were in the low-spin (LS) state at 300 K and exhibited a cooperative spin crossover (SCO) transition with a thermal hysteresis loop at higher temperatures, whereas 3 was in the high-spin (HS) state below 300 K. The optical conductivity spectra for 1 and 3 were calculated from the single-crystal reflection spectra, which were, to the best of our knowledge, the first optical conductivity spectra of SCO compounds. The absorption bands for the LS and HS [Fe(qsal) 2 ] cations were assigned by time-dependent density functional theory calculations. The crystal structures of 1 and 2 consisted of a common one-dimensional (1D) array of the [Fe(qsal) 2 ] cation, whereas that of 3 had an unusual 1D arrangement by π-stacking interactions which has never been reported. The crystal structures in the high-temperature phases for 1 and 2 indicate that large structural changes were triggered by the motion of counter anions. The comparison of the crystal structures of the known [Fe(qsal) 2 ] compounds suggests the significant role of a large non-spherical counter-anion or solvate molecule for the total lattice energy gain in the crystal of a charged complex.

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Fabrication of an all-diamond microelectrode using a chromium mask

Asai K., Einaga Y.

Chemical Communications (Chemical Communications) 55 ( 7 ) 897 - 900 2019

ISSN 13597345

© 2019 The Royal Society of Chemistry. We have developed a new method for fabricating all-diamond microelectrodes. The process comprises three steps: masking the tip of an electrode by electroplating with chromium, depositing undoped diamond, which acts as an insulator on the sides of the electrode, and removing the chromium mask to expose the tip of the electrode. The active area of the electrode can be easily controlled in combination only with a conventional electroplating technique.

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Electrochemical Pinacol Coupling of Acetophenone Using Boron-Doped Diamond Electrode

Nakahara K., Naba K., Saitoh T., Sugai T., Obata R., Nishiyama S., Einaga Y., Yamamoto T.

ChemElectroChem (ChemElectroChem) 6 ( 16 ) 4153 - 4157 2019

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim An electrochemical pinacol coupling reaction of acetophenone using a boron-doped diamond (BDD) electrode has been reported. This transformation is driven by the one-electron reduction of acetophenone on the BDD cathode, followed by an intermolecular radical coupling. Owing to the BDD's outstanding electrochemical properties, the pinacol-type compound has been obtained in good conversion yield. The roles of a supporting electrolyte and solvent were addressed; (1) lithium ions contribute to increase in the reactivity of the radical intermediate. (2) Addition of water promotes the electron transfer process at the BDD surface. The reaction is relatively tolerant to para-substituted acetophenone derivatives. Since electric current is directly employed as reducing reagents to generate a radical intermediate, the reaction is metal-free, sustainable, and inherently safe.

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CO<inf>2</inf> reduction to formic acid at low overpotential on BDD electrodes modified with nanostructured CeO<inf>2</inf>

Verlato E., Barison S., Einaga Y., Fasolin S., Musiani M., Nasi L., Natsui K., Paolucci F., Valenti G.

Journal of Materials Chemistry A (Journal of Materials Chemistry A) 7 ( 30 ) 17896 - 17905 2019

ISSN 20507488

© 2019 The Royal Society of Chemistry. Ceria was deposited onto boron doped polycrystalline diamond (BDD) cathodes, through electrochemically induced precipitation from nitrate-based solutions. The deposits were characterized using SEM-EDS, HRTEM, XRD and XPS. The morphology, thickness and composition of ceria films, which besides CeO2 contained Ce(OH)3 when prepared at very negative potential, were controlled by tuning the deposition parameters. Thin Ce(OH)3-free ceria films allowed CO2 electrochemical reduction at overpotentials below 50 mV, yielding formic acid with faradaic yield higher than 40% and stable performance for many hours. Ceria seemed to act as a co-catalyst that activated CO2 for reduction at the H-terminated BDD surface, because comparable results were not obtained with ceria-coated glassy carbon electrodes.

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Oxidative Cleavage of the Acyl-Carbon Bond in Phenylacetone with Electrogenerated Superoxide Anions

Zhang Y., Sugai T., Yamamoto T., Yamamoto N., Kutsumura N., Einaga Y., Nishiyama S., Saitoh T., Nagase H.

ChemElectroChem (ChemElectroChem) 6 ( 16 ) 4194 - 4198 2019

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim An oxidative cleavage reaction of the acyl−carbon bond in phenylacetone derivatives under cathodic reduction is reported. This particular transformation is driven by the cathodic reduction of dissolved molecular oxygen to superoxide anions. Various cathode materials were examined, and we discovered that boron-doped diamond (BDD) enables highly efficient molecular conversion, owing to BDD's outstanding electrochemical property for utilizing the small amounts of molecular oxygen effectively. The scope of the reaction is broad and can be applied to a variety of substrates, ranging from ketones to esters and amides. As an electric current is directly employed to generate the superoxide anion, the reaction is metal- and catalyst-free. Electro-organic synthesis using the carbon-based BDD electrode thus provides access to sustainable molecular transformations.

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Electrochemical reduction of CO<inf>2</inf> using palladium modified boron-doped diamond electrodes: Enhancing the production of CO

Jiwanti P.K., Einaga Y.

Physical Chemistry Chemical Physics (Physical Chemistry Chemical Physics) 21 ( 28 ) 15297 - 15301 2019

ISSN 14639076

© 2019 the Owner Societies. In recent years, boron-doped diamond (BDD) has been utilized as an electrode for the electrochemical reduction of CO2, and several reports have been published on this. The wide potential window of BDD enables the hydrogen evolution reaction, which competes with CO2 reduction, to be suppressed. On the other hand, the high overpotential is still a problem. We attempted to overcome this problem by depositing metal on the BDD electrode. Pd metal was chosen to modify the surface of the BDD electrode (PdBDD). Employing this electrode at a lower potential of-1.6 V vs. Ag/AgCl, we increased the production of CO (53.3% faradaic efficiency) from the reduction of CO2. We present various attempts made to improve the CO production.

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Electrochemical properties of fluorinated boron-doped diamond electrodes: Via fluorine-containing plasma treatment

Yamaguchi C., Natsui K., Iizuka S., Tateyama Y., Einaga Y.

Physical Chemistry Chemical Physics (Physical Chemistry Chemical Physics) 21 ( 25 ) 13788 - 13794 2019

ISSN 14639076

© the Owner Societies. Since a boron-doped diamond (BDD) exhibits excellent electrode properties such as wide potential window, low back-ground current, and high physical and chemical durability, it has been studied as an electrode material for various electrochemical applications. The electrochemical behavior of BDD depends on the surface termination, which can be easily converted by chemical reactions. Fluorine termination has attracted interest because it exhibits unique surface properties such as high hydrophobicity and a low coefficient of friction, and the electrochemical properties also drastically change. However, so far, it has not been elucidated why fluorinated BDD exhibits specific electrochemical properties. In this article, fluorine-terminated BDD was fabricated by a fluorine-containing plasma treatment, and the electrochemical properties were systematically investigated. Together with experiments, we have calculated the interfacial structures and electronic states of hydrogenated, oxygenated, and fluorinated BDD electrodes. As a result, fluorinated BDD showed lower electrochemical reactivity than hydrogenated and oxygenated BDD. Especially, electron transfer between anionic compound and fluorinated BDD was significantly suppressed. Considered together with theoretical calculations, this reactivity could be attributed to the larger interfacial band bending in fluorinated BDD and electrostatic interactions between BDD and redox species.

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Development of in vivo drug sensing system with needle-type diamond microelectrode

Ogata G., Asai K., Sano Y., Sawamura S., Takai M., Kusuhara H., Einaga Y., Hibino H.

Folia Pharmacologica Japonica (Folia Pharmacologica Japonica) 153 ( 6 ) 273 - 277 2019

ISSN 00155691

© 2019, Japanese Pharmacological Society. All rights reserved. Continuous and real-time measurement of local concentrations of systemically administered drugs in vivo must be crucial for pharmacological studies. Nevertheless, conventional methods require considerable samples quantity and have poor sampling rates. Additionally, they cannot determine how drug kinetics correlates with target function over time. Here, we describe a system with two different sensors. One is a needle-type microsensor composed of boron-doped diamond with a tip of ~40 μm in diameter, and the other is a glass microelectrode. We first tested bumetanide. This diuretic can induce deafness. In the guinea-pig cochlea injected intravenously with bumetanide, the changes of the drug concentration and the extracellular potential underlying hearing were simultaneously measured in real time. We further examined an antiepileptic drug lamotrigine in the rat brain, and tracked its kinetics and at the same time the local field potentials representing neuronal activity. The action of the anticancer reagent doxorubicin was also monitored in the cochlea. This microsensing system may be applied to analyze pharmacokinetics and pharmacodynamics of various drugs at local sites in vivo, and contribute to promoting the pharmacological researches.

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In Situ ATR-IR Observation of the Electrochemical Oxidation of a Polycrystalline Boron-Doped Diamond Electrode in Acidic Solutions

Ogose T., Kasahara S., Ikemiya N., Hoshi N., Einaga Y., Nakamura M.

Journal of Physical Chemistry C (Journal of Physical Chemistry C) 122 ( 48 ) 27456 - 27461 2018.12

ISSN 19327447

© 2018 American Chemical Society. Electrochemical surface oxidation in acidic solutions was investigated on a boron-doped diamond film electrode, fabricated on a silicon prism, using attenuated total reflection infrared spectroscopy. At positive potentials above +1.3 V (reversible hydrogen electrode, RHE), the bands of surface oxygen species appear at 1745 and 1250 cm-1. Since these bands exhibit no isotope shift in deuterium solution, they are assigned to the C=O and C-O stretching modes, respectively. These bands have the maximum intensity at +3.3 V (RHE) and reversibly disappear around +0.9 V (RHE) in the potential step to the negative direction. The potentials at which the bands appear and disappear are identical to those of the anodic and cathodic peaks of the cyclic voltammogram, respectively.

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Electrogenerated Chemiluminescence with Peroxydisulfate as a Coreactant Using Boron Doped Diamond Electrodes

Fiorani A., Irkham, Valenti G., Paolucci F., Einaga Y.

Analytical Chemistry (Analytical Chemistry) 90 ( 21 ) 12959 - 12963 2018.11

ISSN 00032700

© 2018 American Chemical Society. We report on the use of boron doped diamond electrodes for the electrochemiluminescence (ECL) of the coreactant peroxydisulfate and the luminophore ruthenium(II)-tris(2,2′-bipyridine). Compared to common electrode materials (i.e., Pt, Au, glassy carbon), boron doped diamond has a large overpotential for the evolution of hydrogen in aqueous electrolyte solutions. This intrinsic feature enables reductive-oxidation ECL with peroxydisulfate to be obtained without interference from hydrogen evolution and with high reproducible signals and stable emission. We investigated the effects of the peroxydisulfate concentration and the pH on the ECL emission to find the optimal conditions for enhancing the signal.

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Comparison of performance between boron-doped diamond and copper electrodes for selective nitrogen gas formation by the electrochemical reduction of nitrate

Kuang P., Natsui K., Einaga Y.

Chemosphere (Chemosphere) 210 524 - 530 2018.11

ISSN 00456535

© 2018 Elsevier Ltd The electrochemical nitrate reduction by using boron-doped diamond (BDD) and copper (Cu) electrodes was investigated at various potentials. Product selectivity of nitrate reduction was strongly dependent on the applied potential for both electrodes. The highest selectivity of nitrogen gas production was obtained at −2.0 V (vs. Ag/AgCl) by using a BDD electrode with a faradaic efficiency as high as 45.2%. Compared with Cu electrode, nitrate reduction on BDD electrode occurred at more positive potential, and the production of nitrogen gas was larger. The transformation of surface-adsorbed nitrate into molecular nitrogen would be accelerated on BDD electrode with hindering nitrite production. In addition, low concentration of surface-adsorbed hydrogen on the BDD would also retard the ammonia generation, leading to increase in the selectivity of nitrogen gas formation. Meanwhile, BDD electrode could hinder the hydrogen evolution reaction, which enhanced the efficiency for nitrate reduction and decreased energy consumption. BDD electrode has excellent stability to remain better performance for reducing nitrate during electrolysis without any variation of surface morphology or chemical components.

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The local structure in heavily boron-doped diamond and the effect this has on its electrochemical properties

Watanabe T., Yoshioka S., Yamamoto T., Sepehri-Amin H., Ohkubo T., Matsumura S., Einaga Y.

Carbon (Carbon) 137 333 - 342 2018.10

ISSN 00086223

© 2018 Elsevier Ltd Transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS), and first principles calculations of EEL spectra were utilized to elucidate the relationship between the microscopic structure and the electrochemical properties of heavily boron-doped diamond (h-BDD). The electrochemical properties of h-BDD containing 1 at.% and 3 at.% boron are very different. TEM observations showed that 1 at.% h-BDD consists of small densely packed diamond crystallites, while 3 at.% h-BDD contains small voids and a graphite phase partly along the grain boundaries. The EEL spectrum of the grain interior in 1 at.% h-BDD and comparison of this with a theoretical spectrum shows that the boron atoms are mostly dispersed as single isolated substitutional atoms on diamond lattice sites in the grain interior and that only a small amount of sp2-bonded carbon is present. In contrast, in the grain interior of 3 at.% h-BDD, the boron atoms are mostly associated with nearest neighbor boron pairs, and consequently sp2-bonded carbon is formed. Thus, the local structure has a significant effect on the amount of sp2-bonded carbon. The quite different electrochemical properties of the samples are ascribed to the amount of sp2-bonding arising from the different local structures.

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Influence of Electrolyte on the Electrochemical Reduction of Carbon Dioxide Using Boron-Doped Diamond Electrodes

Tomisaki M., Natsui K., Ikemiya N., Nakata K., Einaga Y.

ChemistrySelect (ChemistrySelect) 3 ( 36 ) 10209 - 10213 2018.09

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electrochemical reduction of CO2 to useful compounds have been actively investigated. The faradaic efficiency and selectivity for products of CO2 reduction depend on some factors, such as electrode materials and electrolytes. Recently, boron-doped diamond (BDD) was found to be a promising electrode material for production of formic acid by CO2 reduction, but the influence of electrolytes has not been sufficiently elucidated. Here, we studied the impact of various cations and anions on CO2 reduction using BDD electrodes. The faradaic efficiency for producing formic acid became higher by using larger alkali metal cations, because these hydrated cations would keep the pH near the cathode suitable for CO2 reduction by their buffer effect. Moreover, formic acid was efficiently obtained by using specifically-adsorbed anions such as halides and sulfate. Finally, we achieved the maximum faradaic efficiency for producing formic acid as high as 95% in RbBr aqueous solution.

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Long-Term Continuous Conversion of CO<inf>2</inf> to Formic Acid Using Boron-Doped Diamond Electrodes

Ikemiya N., Natsui K., Nakata K., Einaga Y.

ACS Sustainable Chemistry and Engineering (ACS Sustainable Chemistry and Engineering) 6 ( 7 ) 8108 - 8112 2018.07

© Copyright 2018 American Chemical Society. The long-term durability of boron-doped diamond electrodes (BDD) used continuously in the electrochemical conversion of CO2 to formic acid was investigated. Although the Faradaic efficiency (FE) for the production of formic acid decreased with increasing electrolysis time, the FE was easily recovered by electrochemical oxidation of the BDD electrodes in H2SO4, Na2SO4 or K2SO4 solutions. For practical application, the long-term production of formic acid using BDD electrodes can be successfully accomplished just by successive polarity reversal of plus and minus terminals. Furthermore, at a current density of -20 mA cm-2, the rate of production reached 328 μmol h-1 cm-2, which is the highest value ever obtained using plate electrodes. Consequently, we found that BDD electrodes are ideal for industrial application of CO2 reduction.

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Effect of doping level on the electrochemical reduction of CO<inf>2</inf> on boron-doped diamond electrodes

Xu J., Natsui K., Naoi S., Nakata K., Einaga Y.

Diamond and Related Materials (Diamond and Related Materials) 86 167 - 172 2018.06

ISSN 09259635

© 2018 Elsevier B.V. Boron-doped diamond (BDD) electrodes have been applied on the electrochemical reduction of CO2. Although boron doping level can strongly affect the electrochemical properties of BDD electrodes, there are, so far, no reports about the effect of doping level on the electrochemical reduction of CO2 using BDD electrodes. Here, we investigated the relationship between boron content of BDD electrodes and the products of CO2 reduction. We prepared five kinds of BDD electrodes with various boron contents (0.01%, 0.1%, 0.5%, 1%, and 2%). The highest faradaic efficiency for producing formic acid was achieved by using a BDD electrode with the boron content of 0.1%, and the faradaic efficiency for hydrogen evolution increased with increasing boron content due to narrower potential window of BDD with higher boron content. On the other hand, the faradaic efficiency for producing CO, which was a side product, slightly increased with increasing boron content. This trend suggested that the adsorbability of CO2 and its intermediates could be altered by controlling boron content. The research opens new insights for design and control of boron-doped diamond for the electrochemical reduction of CO2.

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Electrochemical measurement of lamotrigine using boron-doped diamond electrodes

Hanawa Ai, Asai Kai, Ogata Genki, Hibino Hiroshi, Einaga Yasuaki

Electrochimica Acta (Electrochimica Acta) 271 35 - 40 2018.05

ISSN 0013-4686

In this paper we report on a study of the electrochemical behavior of lamotrigine (LTG) using boron-doped diamond (BDD) electrodes. Cyclic voltammetry of LTG in a phosphate buffer solution exhibited an oxidation signal at ca. +1.4 V (vs. Ag/AgCl). A reduction signal at −0.5 to −1.0 V (vs. Ag/AgCl) was observed only after oxidation of LTG. The oxidation signal was due to polymerization of LTG adsorbed on the BDD electrode, while the reduction signal was a consequence of a process involving the reduction of the azo group in the LTG-oxidized product. Continuous measurements of LTG aiming at in vivo monitoring were successfully investigated and an optimized chronoamperometry technique, in which the BDD microelectrode was clamped to the LTG oxidation potential (+1.4 V) for 2 s, then to the LTG reduction potential (−0.6 V) for 2 s, was implemented. The limits of detection (S/N = 3) were estimated to be 29 nM and 130 nM for the oxidation and reduction of LTG, respectively. The use of this chronoamperometry technique enables a high temporal resolution of 4 s for LTG measurements. BDD microelectrodes, therefore, are the ideal electrodes for performing continuous in vivo measurements of LTG.

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Controlled decoration of boron-doped diamond electrodes by electrochemical click reaction (e−CLICK)

Yamamoto Takashi, Akahori Miku, Natsui Keisuke, Saitoh Tsuyoshi, Einaga Yasuaki

Carbon (Carbon) 130 350 - 354 2018.04

ISSN 0008-6223

Controlled surface functionalization of electrode materials is an important technique in various fields such as analytical chemistry, molecular electronics, and molecular recognition in biological systems. In this work, we report the control decoration of boron-doped diamond (BDD) electrodes by electrochemically driven copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition of alkyne and azide (e−CLICK) in which the catalyst is produced by electroreduction of copper(II) species. As the e−CLICK strategy enabled to tune the produced amount of the copper(I) catalyst electrochemically, the alkyne-terminated BDD electrodes were decorated with azide-terminated ferrocene in a controlled manner.

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Molecular engineering of Rashba spin-charge converter

Nakayama Hiroyasu, Yamamoto Takashi, An Hongyu, Tsuda Kento, Einaga Yasuaki, Ando Kazuya

Science Advances (Science Advances) 4 ( 3 ) 2018.03

In heterostructures with broken inversion symmetry, the electrons' motion is coupled to their spin through interface-driven spin-orbit coupling: the Rashba effect. The Rashba effect enables the interconversion between spin and charge currents, offering a variety of novel spintronic phenomena and functionalities. However, despite the significant progress in Rashba physics, controlling the spin-charge conversion in metallic heterostructures remains a major challenge. We show that molecular self-assembly provides a way to engineer the Rashba spin-charge converters. We demonstrate that magnetoresistance and voltage generation originating from the spin-charge conversion in metallic heterostructures can be manipulated by decorating the surface with selfassembled organic monolayers through the cooperative molecular field effect. We also demonstrate reversible phototuning of the spin-charge conversion through light-driven molecular transformations using a molecule that can photoisomerize between the trans and cis states. These findings, with the almost-infinite chemical tunability of organic monolayers, pave the way toward molecular engineering of spin-orbit devices.

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The electrochemical production of C₂/C₃ species from carbon dioxide on copper-modified boron-doped diamond electrodes

Jiwanti Prastika K., Natsui Keisuke, Nakata Kazuya, Einaga Yasuaki

Electrochimica Acta (Electrochimica Acta) 266 414 - 419 2018.03

ISSN 0013-4686

We report on the first observation of the production of C₂/C₃ species from the electrochemical reduction of CO₂ at the surfaces of copper-modified boron-doped diamond (Cu-BDD) electrodes in aqueous media at room temperature and ambient pressure. The product distribution is dependent on the amount of deposited Cu and the applied potential. At low potential, −1.0 V (vs. Ag/AgCl), ethanol was observed as the main product with acetaldehyde and acetone as side products. The highest faradaic efficiencies obtained for ethanol, acetaldehyde and acetone were 42.4%, 13.7% and 7%, respectively. The Cu particles on the surfaces of the BDD electrodes remained stable, showing insignificant differences after the CO₂ electroreduction process under these particular conditions. The efficiency dropped with increasing Cu deposition time and at high reduction potentials. Moreover, we present comparisons with a Cu plate and Cu-modified glassy carbon as working electrodes under the same conditions, which explains the specific behavior of the CO₂ reduction process on the Cu-BDD electrode.

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Contribution of Coulomb Interactions to a Two-Step Crystal Structure Phase Transformation Coupled with a Significant Change in Spin Crossover Behavior for a Series of Charged Fe^II Complexes from 2,6-Bis(2-methylthiazol-4-yl)pyridine

Takahashi Kazuyuki, Okai Mitsunobu, Mochida Tomoyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki, Shiota Yoshihito, Yoshizawa Kazunari, Konaka Hisashi, Sasaki Akito

Inorganic Chemistry (Inorganic Chemistry) 57 ( 3 ) 1277 - 1287 2018.02

ISSN 0020-1669

A series of [Fe^II(L)₂](BF₄)₂ compounds were structurally and physically characterized (L = 2,6-bis(2-methylthiazol-4-yl)pyridine). A crystal structure phase transformation from dihydrate compound 1 to anhydrous compound 3 through partially hydrated compounds 2 and 2′ upon dehydration was found. Compounds 1 and 3 exhibited a gradual spin crossover (SCO) conversion, whereas compounds 2 and 2′ demonstrated two-step and one-step abrupt SCO transitions, respectively. An X-ray single-crystal structural analysis revealed that one-dimensional and two-dimensional Fe cation networks linked by π stacking and sulfur-sulfur interactions were formed in 1 and 3, respectively. A thermodynamic analysis of the magnetic susceptibility for 1, 2′, and 3 suggests that the enthalpy differences may govern SCO transition behaviors in the polymorphic compounds 2′ and 3. A structural comparison between 1 and 3 indicates that the SCO behavior variations and crystal structure transformation in the present [Fe^II(L)₂](BF₄)₂ compounds can be interpreted by the relationship between the lattice enthalpies mainly arising from Coulomb interactions between the Fe cations and BF₄ anions as in typical ionic crystals.

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Stable and Highly Efficient Electrochemical Production of Formic Acid from Carbon Dioxide Using Diamond Electrodes

Natsui Keisuke, Iwakawa Hitomi, Ikemiya Norihito, Nakata Kazuya, Einaga Yasuaki

Angewandte Chemie - International Edition (Angewandte Chemie - International Edition) 57 ( 10 ) 2639 - 2643 2018.01

ISSN 1433-7851

High faradaic efficiencies can be achieved in the production of formic acid (HCOOH) by metal electrodes, such as Sn or Pb, in the electrochemical reduction of carbon dioxide (CO₂). However, the stability and environmental load in using them are problematic. The electrochemical reduction of CO₂ to HCOOH was investigated in a flow cell using boron-doped diamond (BDD) electrodes. BDD electrodes have superior electrochemical properties to metal electrodes, and, moreover, are highly durable. The faradaic efficiency for the production of HCOOH was as high as 94.7%. Furthermore, the selectivity for the production of HCOOH was more than 99%. The rate of the production was increased to 473μmolm^-2s^-1 at a current density of 15mAcm^-2 with a faradaic efficiency of 61%. The faradaic efficiency and the production rate are almost the same as or larger than those achieved using Sn and Pb electrodes. Furthermore, the stability of the BDD electrodes was confirmed by 24h operation.

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A solvent-directed stereoselective and electrocatalytic synthesis of diisoeugenol

Yamamoto Takashi, Riehl Barbara, Naba Keisuke, Nakahara Kenshin, Wiebe Anton, Saitoh Tsuyoshi, Waldvogel Siegfried R., Einaga Yasuaki

Chemical Communications (Chemical Communications) 54 ( 22 ) 2771 - 2773 2018.01

ISSN 1359-7345

A stereoselective and electrocatalytic coupling reaction of isoeugenol has been reported for the first time in a 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)/boron-doped diamond (BDD) electrode system. This particular C-C bond formation and diastereoselectivity is driven by a solvate interaction between the radical species and another isoeugenol molecule. Due to an electrocatalytic cycle, only understoichiometric amounts of charge are necessary. Since electric current is directly employed as the oxidant, the reaction is metal and reagent-free. In addition, the electrolysis can be conducted in a very simple undivided beaker-type cell under constant current conditions. Therefore, the protocol is easy to use, suitable for scale-up, and inherently safe.

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Development of electrochemical applications of boron-doped diamond electrodes

Einaga Y.

Bulletin of the Chemical Society of Japan (Bulletin of the Chemical Society of Japan) 91 ( 12 ) 1752 - 1762 2018

ISSN 00092673

© 2018 The Chemical Society of Japan It is well known that “diamond” has ultra-high hardness and low electrical conductivity. However, introducing dopants such as boron into the diamond lattice during growth can increase its conductivity. Boron-doped diamond (BDD) with high conductivity is attracting increasing attention as one of the next-generation of superior electrode materials. In particular, it is expected that BDD electrodes can help solve some of our environmental problems and also improve our quality of life through their use in biomedical devices. Here, in this article, recent developments in the electrochemical applications of boron-doped diamond (BDD) electrodes are introduced.

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Improvement of microtas for directed evolution of NAD(P)-dependent oxidoreductases

Goto H., Kanai Y., Yotsui A., Shimokihara S., Shitara S., Einaga Y., Matsumoto Y., Miki N., Fujiwara K., Doi N.

22nd International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2018 (22nd International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2018) 4 2247 - 2249 2018

ISSN 9781510897571

Copyright © (2018) by Chemical and Biological Microsystems Society. All rights reserved. Here we report an improved μTAS based on electrochemical measurements and microbeads sorting for screening of NAD(P)-dependent oxidoreductases. By using this system, we measured the activity of model enzymes immobilized on microbeads by detection of NADH with a boron-doped diamond (BDD) electrode in each compartment (∼30 nL) of the microfluidic system. Then, we recovered the magnetic microbeads or the droplets containing genes of enzymes with higher activity by magnetophoretic or dielectrophoretic sorting, respectively. Our μTAS should be useful for directed evolution of various NAD(P)-dependent oxidoreductases with high activity and stability in the future.

Bimetallic Pt–Au nanocatalysts electrochemically deposited on boron-doped diamond electrodes for nonenzymatic glucose detection

Nantaphol Siriwan, Watanabe Takeshi, Nomura Naohiro, Siangproh Weena, Chailapakul Orawon, Einaga Yasuaki

Biosensors and Bioelectronics 98 76 - 82 2017.12

ISSN 0956-5663

The enormous demand for medical diagnostics has encouraged the fabrication of high- performance sensing platforms for the detection of glucose. Nonenzymatic glucose sensors are coming ever closer to being used in practical applications. Bimetallic catalysts have been shown to be superior to single metal catalysts in that they have greater activity and selectivity. Here, we demonstrate the preparation, characterization, and electrocatalytic characteristics of a new bimetallic Pt/Au nanocatalyst. This nanocatalyst can easily be synthesized by electrodeposition by sequentially depositing Au and Pt on the surface of a boron-doped diamond (BDD) electrode. We characterized the nanocatalyst by scanning electron microscopy (SEM), X-ray diffraction (XRD), and voltammetry. The morphology and composition of the nanocatalyst can be easily controlled by adjusting the electrodeposition process and the molar ratio between the Pt and Au precursors. The electrocatalytic characteristics of a Pt/Au/BDD electrode for the nonenzymatic oxidation of glucose were systematically investigated by cyclic voltammetry. The electrode exhibits higher catalytic activity for glucose oxidation than Pt/BDD and Au/BDD electrodes. The best catalytic activity and stability was obtained with a Pt:Au molar ratio of 50:50. Moreover, the presence of Au can significantly enhance the long-term stability and poisoning tolerance during the electro-oxidation of glucose. Measurements of glucose using the Pt/Au/BDD electrode were linear in the range from 0.01 to 7.5 mM, with a detection limit of 0.0077 mM glucose. The proposed electrode performs selective electrochemical analysis of glucose in the presence of common interfering species (e.g., acetaminophen, uric and ascorbic acids), avoiding the generation of overlapping signals from such species.

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Facet-Dependent Temporal and Spatial Changes in Boron-Doped Diamond Film Electrodes due to Anodic Corrosion

Catalan Francesca Celine I., Hayazawa Norihiko, Yokota Yasuyuki, Wong Raymond A., Watanabe Takeshi, Einaga Yasuaki, Kim Yousoo

Journal of Physical Chemistry C 121 ( 48 ) 26742 - 26750 2017.12

ISSN 1932-7447

The progression of corrosion in polycrystalline boron-doped diamond (BDD) thin film electrode is explored as the electrode undergoes high-current density anodic treatments with organic compounds. Micro-Raman spectroscopy and spectral mapping indicate that anodic corrosion is initiated by the conversion of sp³ diamond to amorphous sp² carbon at the surface, which are then removed after longer anodic treatment. Polarized Raman analysis reveals that corrosion-induced changes on the surface are specific to (100)-grain facets and (111)-grain edges. X-ray photoelectron spectroscopic measurements suggest that carbonyl groups consequently form on these specific sites and act as an intermediate toward the etching of the surface. This process exposes and subsequently removes the subsurface boron atoms, thus reducing the doping density. The observed crystal grain orientation dependence of the corrosion process provides new insights toward a better understanding of degradation in BDD electrodes.

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Spin-singlet transition in the magnetic hybrid compound from a spin-crossover Fe(III) cation and π-radical anion

Takahashi Kazuyuki, Sakurai Takahiro, Zhang Wei Min, Okubo Susumu, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki, Mori Hatsumi

Inorganics 5 ( 3 ) 2017.09

To develop a new spin-crossover functional material, a magnetic hybrid compound [Fe(qsal)₂][Ni(mnt)₂] was designed and synthesized (Hqsal = N-(8-quinolyl)salicylaldimine, mnt = maleonitriledithiolate). The temperature dependence of magnetic susceptibility suggested the coexistence of the high-spin (HS) Fe(III) cation and π-radical anion at room temperature and a magnetic transition below 100 K. The thermal variation of crystal structures revealed that strong π-stacking interaction between the π-ligand in the [Fe(qsal)₂] cation and [Ni(mnt)₂] anion induced the distortion of an Fe(III) coordination structure and the suppression of a dimerization of the [Ni(mnt)₂] anion. Transfer integral calculations indicated that the magnetic transition below 100 K originated from a spin-singlet formation transformation in the [Ni(mnt)₂] dimer. The magnetic relaxation of Mössbauer spectra and large thermal variation of a g-value in electron paramagnetic resonance spectra below the magnetic transition temperature implied the existence of a magnetic correlation between d-spin and π-spin.

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A microsensing system for the in vivo real-time detection of local drug kinetics

Ogata Genki, Ishii Yuya, Asai Kai, Sano Yamato, Nin Fumiaki, Yoshida Takamasa, Higuchi Taiga, Sawamura Seishiro, Ota Takeru, Hori Karin, Maeda Kazuya, Komune Shizuo, Doi Katsumi, Takai Madoka, Findlay Ian, Kusuhara Hiroyuki, Einaga Yasuaki, Hibino Hiroshi

Nature Biomedical Engineering 1 ( 8 ) 654 - 666 2017.08

Real-time recording of the kinetics of systemically administered drugs in in vivo microenvironments may accelerate the development of effective medical therapies. However, conventional methods require considerable analyte quantities, have low sampling rates and do not address how drug kinetics correlate with target function over time. Here, we describe the development and application of a drug-sensing system consisting of a glass microelectrode and a microsensor composed of boron-doped diamond with a tip of around 40 μm in diameter. We show that, in the Guinea pig cochlea, the system can measure - simultaneously and in real time - changes in the concentration of bumetanide (a diuretic that is ototoxic but applicable to epilepsy treatment) and the endocochlear potential underlying hearing. In the rat brain, we tracked the kinetics of the drug and the local field potentials representing neuronal activity. We also show that the actions of the antiepileptic drug lamotrigine and the anticancer reagent doxorubicin can be monitored in vivo. Our microsensing system offers the potential to detect pharmacological and physiological responses that might otherwise remain undetected.

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Hydroxide Ion Oxidation in Aqueous Solutions Using Boron-Doped Diamond Electrodes

Watanabe Takeshi, Einaga Yasuaki

Analytical Chemistry 89 ( 13 ) 7139 - 7144 2017.07

ISSN 0003-2700

The electrochemical oxidation behavior of hydroxide ions at the surface of boron-doped diamond (BDD) electrodes is presented. The hydroxide ion oxidation behavior was found to be affected by the surface conditions of the BDD electrode. Over the NaOH concentration range of 0.5-10 mM, a well-defined voltammetric wave attributed to hydroxide ion oxidation was observed at ∼1.25 V versus a Ag/AgCl reference electrode when using an anodically oxidized BDD (AO-BDD) electrode, while it was observed at around ∼1.15 V when a cathodically reduced BDD (CR-BDD) electrode was used. Although the hydroxide ion oxidation profiles were slightly different for the AO-BDD and CR-BDD electrodes, the peak currents was each found to have linear relationships with the NaOH concentration over the same range.

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Photo-modulation of superconducting and magnetic properties

Yamamoto Takashi, Natsui Keisuke, Einaga Yasuaki

285 - 299 2017.05

In this chapter, photo-modulation of superconducting and magnetic properties is described. First, the superconducting property of a boron-doped diamond is investigated, in which the critical current density varies dramatically between the hydrogen- and oxygen-terminated diamond. Second, the superconducting diamond is modified with an azobenzene molecular layer to modulate the superconductivity upon photoirradiation. In this composite superconductor, the critical current density is reversibly amplified by 55% upon photoisomerization of the azobenzene layer. Third, Prussian Blue, a coordination polymer, is integrated with the semiconducting titanium oxide nanosheets to modulate the magnetic property upon photoirradiation. In this magnetic heterostructure, photoinduced magnetic phase transition of Prussian Blue is present by injecting photoexcited electrons from titanium oxide nanosheets.

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Phase 1 study of sulfasalazine and cisplatin for patients with CD44v-positive gastric cancer refractory to cisplatin (EPOC1407)

Shitara Kohei, Doi Toshihiko, Nagano Osamu, Fukutani Miki, Hasegawa Hiromi, Nomura Shogo, Sato Akihiro, Kuwata Takeshi, Asai Kai, Einaga Yasuaki, Tsuchihashi Kenji, Suina Kentaro, Maeda Yusuke, Saya Hideyuki, Ohtsu Atsushi

Gastric Cancer 1 - 6 2017.05

ISSN 1436-3291

A previous dose-escalation study of sulfasalazine (SSZ), an inhibitor of cystine-glutamate exchange transporter xc (–), in the variant form of CD44 (CD44v)-positive cancer stem cells (CSCs) suggested that administration of SSZ induces the reduction of CD44v-positive cells and intracellular reduced glutathione (GSH) levels in patients with advanced gastric cancer (AGC). Here we report a study to evaluate SSZ in combination with cisplatin in patients with CD44v-expressing AGC refractory to cisplatin. SSZ was given by oral administration four times daily with 2 weeks on and 1 week off. Cisplatin at 60 mg/m² was administered every 3 weeks. Of the 15 patients who underwent prescreening of CD44v expression, 8 patients were positive, and 7 patients were treated with the dose level of SSZ at 6 g/day. One patient experienced dose-limiting toxicity (DLT) as grade 3 anorexia. Although no other patients experienced DLT, 4 patients required dose interruption or reduction of SSZ; thus, we terminated further dose escalation. No patient achieved objective response, but 1 patient completed six cycles with stable disease for more than 4 months as well as reduction of intratumoral GSH level. The combination of SSZ plus cisplatin was manageable, although dose modification was frequently required during a short observational period.

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Anodic stripping voltammetry of nickel ions and nickel hydroxide nanoparticles at boron-doped diamond electrodes

Musyarofah N. R.R., Gunlazuardi J., Einaga Y., Ivandini T. A.

IOP Conference Series: Materials Science and Engineering 188 ( 1 ) 2017.05

ISSN 1757-8981

Anodic stripping voltammetry (ASV) of nickel ions in phosphate buffer solution (PBS) have been investigated at boron-doped diamond (BDD) electrodes. The deposition potential at 0.1 V (vs. Ag/AgCl) for 300 s in 0.1 M PBS pH 3 was found as the optimum condition. The condition was applied for the determination of nickel contained in nickel hydroxide nanoparticles. A linear calibration curve can be achieved of Ni(OH)₂-NPs in the concentration range of x to x mM with an estimated limit of detection (LOD) of 5.73 × 10^-6 mol/L.

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Gigantic Photomagnetic Effect at Room Temperature in Spiropyran-Protected FePt Nanoparticles

Yamamoto Takashi, Yurieva Elena A., Tsuda Kento, Hosomi Tomoko, Aldoshin Sergey M., Einaga Yasuaki

Physica Status Solidi - Rapid Research Letters 2017

ISSN 1862-6254

A key issue in molecular electronics is the control of electronic states and properties by optical stimuli, which enables fast and high-density data storage. In this article, we report preparation of a photoswitchable room-temperature ferromagnetic material using FePt nanoparticles protected with a photochromic spiropyran ligand. Magnetic properties were examined with a field-dependent isothermal magnetization, and a photomagnetic effect was measured at room temperature. These measurements revealed room-temperature ferromagnetism and reversible switching of magnetization by 60% upon photochromic reaction of the spiropyran ligand. This gigantic photomagnetic effect is explained as spiropyran's large change in the dipole moment during photochromic reaction that tunes the magnitude of electron transfer at the interface.

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Polycrystalline boron-doped diamond electrodes for electrocatalytic and electrosynthetic applications

Ivandini Tribidasari A., Einaga Yasuaki

Chemical Communications 53 ( 8 ) 1338 - 1347 2017

ISSN 1359-7345

Boron-doped diamond (BDD) electrodes are recognized as being superior to other electrode materials due to their outstanding chemical and dimensional stability, their exceptionally low background current, the extremely wide potential window for water electrolysis that they have, and their excellent biocompatibility. However, whereas these properties have been utilized in the rapid development of electroanalytical applications, very few studies have been done in relation to their applications in electrocatalysis or electrosynthesis. In this report, following on from reports of the electrosynthesis of various products through anodic and cathodic reactions using BDD electrodes, the potential use of these electrodes in electrosynthesis is discussed.

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Cooperative spin-crossover transition from three-dimensional purely π-stacking interactions in a neutral heteroleptic azobisphenolate Fe^III complex with a N₃O₃ coordination sphere

Murata Suguru, Takahashi Kazuyuki, Mochida Tomoyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki

Dalton Transactions 46 ( 18 ) 5786 - 5789 2017

ISSN 1477-9226

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Effect of alkali-metal cations on the electrochemical reduction of carbon dioxide to formic acid using boron-doped diamond electrodes

Ikemiya Norihito, Natsui Keisuke, Nakata Kazuya, Einaga Yasuaki

RSC Advances 7 ( 36 ) 22510 - 22514 2017

ISSN 2046-2069

The electrochemical reduction of carbon dioxide in aqueous solutions using boron-doped diamond (BDD) electrodes was investigated at ambient pressure and temperature. We discuss the effects of the alkali-metal (AM) cations, K⁺, Na⁺, Rb⁺ and Cs⁺, on the faradaic efficiency (FE) for the formation of formic acid. An FE of 71% was achieved in the case of a 0.075 M Rb⁺ solution neutralized to pH 6.2 by the addition of HCl. In the case of a Cs⁺ solution neutralized to pH 6.2, the highest FE was obtained with the more dilute concentration of 0.02 M. Of the four different solutions examined, the lowest FE was observed for the Na⁺ solution. Moreover, we found that the productivity for the production of formic acid is higher at higher current densities.

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Asymmetric induction in cyclohexadienones carrying α-D-glucopyranosyl moiety

Yajima Saki, Saitoh Tsuyoshi, Kawa Kohei, Nakamura Kensuke, Nagase Hiroshi, Einaga Yasuaki, Nishiyama Shigeru

Tetrahedron 72 ( 51 ) 8428 - 8435 2016.12

ISSN 0040-4020

Cyclohexadienone derivatives possessing α-D-glucopyranosyl moiety were designed and synthesized using chemical oxidation or electrochemical oxidation with boron-doped diamond electrode in the final stage. In the chiral induction studies, catalytic hydrogenation provided high diastereoselectivity (dr ratio: > 9:1). Conformational analyses of the C-glucoside structures were performed by NOE experiments and force field calculations, and supported the observed regio-selectivity.

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Co-reactant-on-Demand ECL

Watanabe Takeshi, Fiorani Andrea, Valenti Giovanni, Paolucci Francesco, Einaga Yasuaki

Journal of the American Chemical Society 138 ( 48 ) 15636 - 15641 2016.12

ISSN 0002-7863

A novel co-reactant-free electrogenerated chemiluminescence (ECL) system is developed where Ru(bpy)₃ ²⁺ emission is obtained on boron-doped diamond (BDD) electrodes. The method exploits the unique ability of BDD to operate at very high oxidation potential in aqueous solutions and to promote the conversion of inert SO₄ ^2- into the reactive co-reactant S₂O₈ ^2-. This novel procedure is rather straightforward, not requiring any particular electrode geometry, and since the co-reactant is only generated in situ, the interference with biological samples is minimized. The underlying mechanism is similar to that of the Ru(bpy)₃ ²⁺/S₂O₈ ^2- system; however, the intensity of the emitted signal increases linearly with [SO₄ ^2-] up to ∼0.6 M, with possible implications for analytical uses of the proposed procedure.

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A Study on Electrolytic Corrosion of Boron-Doped Diamond Electrodes when Decomposing Organic Compounds

Kashiwada Takeshi, Watanabe Takeshi, Ootani Yusuke, Tateyama Yoshitaka, Einaga Yasuaki

ACS Applied Materials and Interfaces 8 ( 42 ) 28299 - 28305 2016.10

ISSN 1944-8244

Electrolytic corrosion of boron-doped diamond (BDD) electrodes after applying a high positive potential to decompose organic compounds in aqueous solution was studied. Scanning electron microscopy images, Raman spectra, and glow discharge optical emission spectroscopy revealed that relatively highly boron-doped domains were primarily corroded and relatively low boron-doped domains remained after electrolysis. The corrosion due to electrolysis was observed especially in aqueous solutions of acetic acid or propionic acid, while it was not observed in other organic compounds such as formic acid, glucose, and methanol. Electron spin resonance measurements after electrolysis in the acetic acid solution revealed the generation of methyl radicals on the BDD electrodes. Here, the possible mechanisms for the corrosion are discussed. Dangling bonds may be formed due to abstraction of OH groups from C-OH functional groups by methyl radicals generated on the surface of the BDD electrodes. As a result, the sp³ diamond structure would be converted to the sp² carbon structure, which can be easily etched. Furthermore, to prevent electrolytic corrosion during electrolysis, both the current density and the pH condition in the aqueous solution were optimized. At low current densities or high pH, the BDD electrodes were stable without electrolytic corrosion even in the acetic acid aqueous solution.

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Continuous and selective measurement of oxytocin and vasopressin using boron-doped diamond electrodes

Asai Kai, Ivandini Tribidasari A., Einaga Yasuaki

Scientific Reports 6 2016.09

ISSN 2045-2322

The electrochemical detection of oxytocin using boron-doped diamond (BDD) electrodes was studied. Cyclic voltammetry of oxytocin in a phosphate buffer solution exhibits an oxidation peak at +0.7 V (vs. Ag/AgCl), which is attributable to oxidation of the phenolic group in the tyrosyl moiety. Furthermore, the linearity of the current peaks obtained in flow injection analysis (FIA) using BDD microelectrodes over the oxytocin concentration range from 0.1 to 10.0 μM with a detection limit of 50 nM (S/N = 3) was high (R² = 0.995). Although the voltammograms of oxytocin and vasopressin observed with an as-deposited BDD electrode, as well as with a cathodically-reduced BDD electrode, were similar, a clear distinction was observed with anodically-oxidized BDD electrodes due to the attractive interaction between vasopressin and the oxidized BDD surface. By means of this distinction, selective measurements using chronoamperometry combined with flow injection analysis at an optimized potential were demonstrated, indicating the possibility of making selective in situ or in vivo measurements of oxytocin.

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The reduction behavior of free chlorine at boron-doped diamond electrodes

Watanabe Takeshi, Akai Kazumi, Einaga Yasuaki

Electrochemistry Communications 70 18 - 22 2016.09

ISSN 1388-2481

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Highly sensitive detection of influenza virus by boron-doped diamond electrode terminated with sialic acid-mimic peptide

Matsubara Teruhiko, Ujie Michiko, Yamamoto Takashi, Akahori Miku, Einaga Yasuaki, Sato Toshinori

Proceedings of the National Academy of Sciences of the United States of America 113 ( 32 ) 8981 - 8984 2016.08

ISSN 0027-8424

The progression of influenza varies according to age and the presence of an underlying disease; appropriate treatment is therefore required to prevent severe disease. Anti-influenza therapy, such as with neuraminidase inhibitors, is effective, but diagnosis at an early phase of infection before viral propagation is critical. Here, we show that several dozen plaque-forming units (pfu) of influenza virus (IFV) can be detected using a boron-doped diamond (BDD) electrode terminated with a sialic acid-mimic peptide. The peptide was used instead of the sialyloligosaccharide receptor, which is the common receptor of influenza A and B viruses required during the early phase of infection, to capture IFV particles. The peptide, which was previously identified by phage-display technology, was immobilized by click chemistry on the BDD electrode, which has excellent electrochemical characteristics such as low background current and weak adsorption of biomolecules. Electrochemical impedance spectroscopy revealed that H1N1 and H3N2 IFVs were detectable in the range of 20-500 pfu by using the peptide-terminated BDD electrode. Our results demonstrate that the BDD device integrated with the receptor-mimic peptide has high sensitivity for detection of a low number of virus particles in the early phase of infection.

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Corrigendum to 'Microfluidic platform for environmental contaminants sensing and degradation based on boron-doped diamond electrodes' [Biosens. Bioelectron. 08/75 (2015) 365-374].doi

Medina-Sánchez Mariana, Mayorga-Martinez Carmen C., Watanabe Takeshi, Ivandini Tribidasari A., Honda Yuki, Pino Flavio, Nakata Kazuya, Fujishima Akira, Einaga Yasuaki, Merkoçi Arben

Biosensors and Bioelectronics 79 946 2016.05

ISSN 0956-5663

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The role of coulomb interactions for spin crossover behaviors and crystal structural transformation in novel anionic fe(III) complexes from a π-extended ono ligand

Murata Suguru, Takahashi Kazuyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki, Shiota Yoshihito, Yoshizawa Kazunari

Crystals 6 ( 5 ) 2016.05

ISSN 2073-4352

To investigate the π-extension effect on an unusual negative-charged spin crossover (SCO) Fe^III complex with a weak N₂O₄ first coordination sphere, we designed and synthesized a series of anionic Fe^III complexes from a π-extended naphthalene derivative ligand. Acetonitrile-solvate tetramethylammonium (TMA) salt 1 exhibited an SCO conversion, while acetone-solvate TMA salt 2 was in a high-spin state. The crystal structural analysis for 2 revealed that two-leg ladder-like cation-anion arrays derived from π-stacking interactions between π-ligands of the Fe^III complex anion and Coulomb interactions were found and the solvated acetone molecules were in one-dimensional channels between the cation-anion arrays. A desolvation-induced single-crystal-to-single-crystal transformation to desolvate compound 2’ may be driven by Coulomb energy gain. Furthermore, the structural comparison between quasi-polymorphic compounds 1 and 2 revealed that the synergy between Coulomb and π-stacking interactions induces a significant distortion of coordination structure of 2.

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Anodic stripping voltammetry of synthesized CdS nanoparticles at boron-doped diamond electrodes

Hayat Mohammad, Ivandini Tribidasari A., Saepudin Endang, Einaga Yasuaki

2016.04

Cadmium sulphide (CdS) nanoparticles were chemically synthesized using reverse micelles microreactor methods. By using different washing treatments, UV-Vis spectroscopy showed that the absorption peaks appeared at 465 nm, 462 nm, 460 nm, and 459 nm respectively for CdS nanoparticles without and with 1, 2, and 3 times washing treatments using pure water. In comparison with the absorbance peak of bulk CdS at 512 nm, the shifted absorption peaks, indicates that the different sizes of CdS can be prepared. Anodic stripping voltammetry of the CdS nanoparticles was then studied at a boron-doped diamond electrode using 0.1 M KClO₄ and 0.1 M HClO₄ as the electrolytes. A scan rate of 100 mV/s with a deposition potential of-1000 mV (vs. Ag/AgCl) for 60 s at a potential scan from-1600 mV to +800 mV (vs. Ag/AgCl) was applied as the optimum condition of the measurements. Highly-accurate linear calibration curves (R² = 0.99) in 0.1 M HClO₄ with the sensitivity of 0.075 mA/mM and the limit of detection of 81 μM in 0.1 M HClO₄ can be achieved, which is promising for an application of CdS nanoparticles as a label for biosensors.

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Screening metal nanoparticles using boron-doped diamond microelectrodes

Ivandini Tribidasari A., Rangkuti Prasmita K., Einaga Yasuaki

2016.04

Boron-doped diamond (BDD) microelectrodes were used to observe the correlation between electrocatalytic currents caused by individual Pt nanoparticle (Pt-np) collisions at the electrode. The BDD microelectrodes, ∼20 μm diameter and ∼2 μm particle size, were fabricated at the surface of tungsten wires. Pt-np with a size of 1 to 5 nm with agglomerations up to 20 nm was used for observation. The electrolytic currents were observed via catalytic reaction of 15 mM hydrazine in 50 mM phosphate buffer solution at Pt-np at 0.4 V when it collides with the surface of the microelectrodes. The low current noise and wider potential window in the measurements using BDD microelectrode produced a better results, which represents a better correlation to the TEM result of the Pt-np, compared to when gold microelectrodes was used.

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Zanamivir immobilized magnetic beads for voltammetric measurement of neuraminidase at gold-modified boron doped diamond electrode

Wahyuni Wulan Tri, Ivandini Tribidasari A., Saepudin Endang, Einaga Yasuaki

2016.04

Biomolecule modified magnetic beads has been widely used in separation and sensing process. This study used streptavidin modified magnetic beads to immobilize biotin modified zanamivir. Biotin-streptavidin affinity facilitates immobilization of zanamivir on magnetic beads. Then interaction of zanamivir and neuraminidase was adopted as basic for enzyme detection. Detection of neuraminidase was performed at gold modified BDD using cyclic voltammetry technique. The measurement was carried out based on alteration of electrochemical signals of working electrode as neuraminidase response. The result showed that zanamivir was successfully immobilized on magnetic beads. The optimum amount of magnetic beads for zanamivir immobilization was 120 ug. Linear responses of neuraminidase were detected in concentration range of 0-15 mU. Detection limit (LOD) of measurement was 2.32 mU (R2 = 0.959) with precision as % RSD of 1.41%. Measurement of neuraminidase on magnetic beads could be also performed in the presence of mucin matrix. The linearity range was 0-8 mU with LOD of 0.64 mU (R2 = 0.950) and % RSD of 7.25%.

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Electroreduction of CO₂ using copper-deposited on boron-doped diamond (BDD)

Panglipur Hanum Sekar, Ivandini Tribidasari A., Wibowo Rahmat, Einaga Yasuaki

2016.04

Electroreduction of CO₂ was studied at copper-modified boron-doped diamond (Cu-BDD) electrodes as the working electrode. The Cu-BDD electrodes were prepared by electrochemical reduction with various concentrations of CuSO₄ solutions. FE-SEM was utilized to characterize the electrodes. At Cu-BDD electrodes, a reduction peak at around-1.2 V (vs Ag/AgCl) attributtable to CO₂ reductions could be observed by cyclic voltammetry technique of CO₂ bubbled in water containing 0.1M NaCl. Accordingly, electroreduction of CO₂ was conducted at-1.2 V (vs Ag/AgCl) using amperometry technique. The chemical products of the electroreduction analyzed by using HPLC showed the formation of formaldehyde, formic acid, and acetic acid at Cu-BDD electrodes.

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Dose-escalation study for the targeting of CD44v⁺ cancer stem cells by sulfasalazine in patients with advanced gastric cancer (EPOC1205)

Shitara Kohei, Doi Toshihiko, Nagano Osamu, Imamura Chiyo K., Ozeki Takeshi, Ishii Yuya, Tsuchihashi Kenji, Takahashi Shunji, Nakajima Takako E., Hironaka Shuichi, Fukutani Miki, Hasegawa Hiromi, Nomura Shogo, Sato Akihiro, Einaga Yasuaki, Kuwata Takeshi, Saya Hideyuki, Ohtsu Atsushi

Gastric Cancer 1 - 9 2016.04

ISSN 1436-3291

Background: Cancer stem cells (CSCs) have enhanced mechanisms of protection from oxidative stress. A variant form of CD44 (CD44v), a major CSC marker, was shown to interact with xCT, a subunit of cystine–glutamate transporter, which maintains high levels of intracellular reduced glutathione (GSH) which defend the cell against oxidative stress. Sulfasalazine (SSZ) is an inhibitor of xCT and was shown to suppress the survival of CD44v-positive stem-like cancer cells both in vitro and in vivo. To find the dose of SSZ which can safely reduce the population of CD44v-positive cells in tumors, a dose-escalation study in patients with advanced gastric cancer was conducted. Methods: SSZ was given four times daily by oral administration with 2 weeks as one cycle. Tumor biopsies were obtained before and after 14 days of administration of SSZ to evaluate expression of CD44v and the intratumoral level of GSH. Results: Eleven patients were enrolled and received a dosage from 8 to 12 g/day. Safety was confirmed up to a dosage of 12 g/day, which was considered the maximum tolerated dose. Among the eight patients with CD44v-positive cells in their pretreatment biopsy samples, the CD44v-positive cancer cell population appeared to be reduced in the posttreatment biopsy tissues of four patients. Intratumoral GSH levels were also decreased in two patients, suggesting biological effectiveness of SSZ at 8 g/day or greater. Conclusions: This is the first study of SSZ as an xCT inhibitor for targeting CSCs. Reduction of the levels of CD44v-positive cells and GSH was observed in some patients, consistent with the mode of action of SSZ in CSCs.

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Development of neuraminidase detection using gold nanoparticles boron-doped diamond electrodes

Wahyuni Wulan T., Ivandini Tribidasari A., Saepudin Endang, Einaga Yasuaki

Analytical Biochemistry 497 68 - 75 2016.03

ISSN 0003-2697

Gold nanoparticles-modified boron-doped diamond (AuNPs-BDD) electrodes, which were prepared with a self-assembly deposition of AuNPs at amine-terminated boron-doped diamond, were examined for voltammetric detection of neuraminidase (NA). The detection method was performed based on the difference of electrochemical responses of zanamivir at gold surface before and after the reaction with NA in phosphate buffer solution (PBS, pH 5.5). A linear calibration curve for zanamivir in 0.1 M PBS in the absence of NA was achieved in the concentration range of 1 × 10^-6 to 1 × 10^-5 M (R² = 0.99) with an estimated limit of detection (LOD) of 2.29 × 10^-6 M. Furthermore, using its reaction with 1.00 × 10^-5 M zanamivir, a linear calibration curve of NA can be obtained in the concentration range of 0-12 mU (R² = 0.99) with an estimated LOD of 0.12 mU. High reproducibility was shown with a relative standard deviation (RSD) of 1.14% (n = 30). These performances could be maintained when the detection was performed in mucin matrix. Comparison performed using gold-modified BDD (Au-BDD) electrodes suggested that the good performance of the detection method is due to the stability of the gold particles position at the BDD surface.

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A New Family of Anionic Fe^III Spin Crossover Complexes Featuring a Weak-Field N₂O₄ Coordination Octahedron

Takahashi Kazuyuki, Kawamukai Kiko, Okai Mitsunobu, Mochida Tomoyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki, Shiota Yoshihito, Yoshizawa Kazunari

Chemistry - A European Journal 22 ( 4 ) 1253 - 1257 2016.01

ISSN 0947-6539

Unprecedented anionic Fe^III spin crossover (SCO) complexes involving a weak-field O,N,O-tridentate ligand were discovered. The SCO transition was evidenced by the temperature variations in magnetic susceptibility, Mössbauer spectrum, and coordination structure. The DFT calculations suggested that larger coefficients on the azo group in the HOMO-1 of a ligand might contribute to the enhancement of a ligand-field splitting energy. The present anionic SCO complex also exhibited the light- induced excited-spin-state trapping effect. Photoinduced spin transition: Unprecedented anionic spin crossover (SCO) complexes involving a weak-field Fe^IIIN₂O₄ coordination sphere were discovered. The tetramethylammonium salt of the depicted SCO anion exhibited the light-induced excited-spin-state trapping effect, which is quite rare in Fe^III SCO complexes (see scheme).

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Microfluidic platform for environmental contaminants sensing and degradation based on boron-doped diamond electrodes

Medina-Sánchez Mariana, Mayorga-Martinez Carmen C., Watanabe Takeshi, Ivandini Tribidasari A., Honda Yuki, Pino Flavio, Nakata Azuya, Fujishima Akira, Einaga Yasuaki, Merkoçi Arben

Biosensors and Bioelectronics 75 365 - 374 2016.01

ISSN 0956-5663

We have developed a lab-on-a-chip (LOC) platform for electrochemical detection and degradation of the pesticide atrazine (Atz). It is based on boron-doped diamond (BDD) electrodes and a competitive magneto-enzyme immunoassay (EIA) that enables high sensitivity. To detect the enzymatic reaction, we employed a BDD electrode modified with platinum nanoparticles (PtNPs), as a highly conductive catalytic transducer. Chronoamperometry revealed a limit of detection (LOD) of 3.5pM for atrazine, which, to the best of our knowledge, is one of the lowest value published to date. Finally, we degraded Atz in the same platform, using a bare BDD electrode that features remarkable corrosion stability, a wide potential window, and much higher O<inf>2</inf> overvoltage as compared to conventional electrodes. These characteristics enable the electrode to produce a greater amount of HO• on the anode surface than do conventional electrodes and consequently, to destroy the pollutant more rapidly. Our new LOC platform might prove interesting as a smart system for detection and remediation of diverse pesticides and other contaminants.

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Surface Termination Effect of Boron-Doped Diamond on the Electrochemical Oxidation of Adenosine Phosphate

Asai Kai, Ivandini Tribidasari A., Falah Muhammad M., Einaga Yasuaki

Electroanalysis 28 ( 1 ) 177 - 182 2016.01

ISSN 1040-0397

Electrochemical oxidation of adenosine phosphates, including adenosine 5'-monophosphate (AMP), adenosine 5'-diphosphate (ADP), and adenosine 5'-triphosphate (ATP), have been studied using boron-doped diamond (BDD) electrodes. Cyclic voltammograms in phosphate buffer solution pH7.4 showed a typical oxidation peak at the potential of around +1.3V (vs. Ag/AgCl) attributable to the oxidation of adenine base moiety. This peak appears at both cathodically and anodically treated BDD. However, investigation at low pH showed, whereas the oxidation peak could be well observed for the oxidation of each AMP, ADP, and ATP at cathodically treated BDD, it was only found for the oxidation of AMP at anodically-treted BDD electrodes. Linear calibration curve can be achieved in the concentration range of 20 to 200μM with an average detection limit of 2μM (S/N=3). Furthermore, cathodic treatment has demonstrated its ability to maintain the electrode surface from biofouling, resulting in the excellent stability of current responses.

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Development of electrochemical oxygen demand measurement cells using a diamond electrode

Kondo Takeshi, Hoshin Masaki, Watanabe Takeshi, Aikawa Tatsuo, Yuasa Makoto, Einaga Yasuaki

Analytical Sciences 32 ( 12 ) 1381 - 1384 2016

ISSN 0910-6340

Electrolytic cells for electrochemical oxygen demand (ECOD) measurements based on total electrolytic decomposition at a boron-doped diamond (BDD) electrode were developed for rapid measurement of organic pollutants at low concentrations. Using improved electrolytic cells designed for efficient mass transfer, the ECOD for 10 μM potassium hydrogen phthalate (theoretical ECOD: 2.3 mg-O₂ L^-1) was determined in a relatively short electrolysis time. Thus, ECOD measurements using these cells would be useful for estimating organic water pollution in industrial waste and lake water.

Co-Fe Prussian Blue analogue intercalated into diamagnetic Mg-Al layered double hydroxides

Zhang Cuijuan, Yamamoto Takashi, Einaga Yasuaki

Nanomaterials and Nanotechnology 6 ( 1 ) 2016

A heterostructure of diamagnetic magnesium-aluminium layered double hydroxides (Mg-Al LDHs) and photomagnetic cobalt-iron Prussian Blue analogue (Co-Fe PBA) was designed, synthesized and then designated as LDH-PB. The cyanide-bridged Co-Fe PBA was two-dimensionally intercalated into the Mg-Al LDH template by the stepwise anion exchange method. LDH-PB showed ferrimagnetic properties with in-plane antiferromagnetic exchange interactions, as well as small photo-induced magnetization by visible light illumination due to the low dimensional structures and the characteristic photo-induced electronic states of the mixed valence of Fe^III(low spin, S = 1/2)-CN-Co^II(high spin, S = 3/2)-NC-Fe^II (low spin, S = 0).

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Preparation of dihydroquinazoline carbohydrazone Fe(II) complexes for spin crossover

Shen Fu Xing, Huang Wei, Yamamoto Takashi, Einaga Yasuaki, Wu Dayu

New Journal of Chemistry 40 ( 5 ) 4534 - 4542 2016

ISSN 1144-0546

Dihydroquinazoline Fe^II complexes, namely [Fe(pq-R)₂](X)₂·xCH₃OH·yCH₃CN·zH₂O (R = 2-py: X = ClO₄ ^-, x = 1, y = 0, z = 2 (1), BF₄ ^-, x = 0, y = 2, z = 1.75 (2), CF₃SO₃ ^-, x = 1, y = 1, z = 0 (3); and X = ClO₄ ^-: R = 2-OCH₃, x = 0, y = 0, z = 1 (4), R = 3-OCH₃, x = 0, y = 0, z = 1 (5)), were prepared and the effects of the solvent, counteranion and ligand substituent on spin crossover properties were discussed. Comparison of X-ray diffraction data for these complexes revealed the sole presence of high-spin Fe^II at 298 K and the bond distances around the Fe^II center at low temperature fall much closer to those at high temperature, which is consistent with variable-temperature dc magnetic susceptibility data. However, the loss of solvent induced a significant change in the spin state of complexes 1 and 2. Moreover, fits to magnetic data of the desolvated samples provide crossover temperatures of T_1/2 = 182.9(6), 157.0(8) and 138.3(5) K for 1-des (ClO₄ ^-), 2-des (BF₄ ^-) and 3-des (CF₃SO₃ ^-), respectively, indicative of the anion-dependent transition temperature. The cooperativity operating in the complexes is thought to be mainly from the intermolecular π⋯π interactions between dihydroquinazoline rings on the neighboring molecules. The ligand substituent effect was also investigated on Fe^II SCO properties. This work revealed the spin crossover properties of new types of dihydroquinazoline Fe(ii) complexes, including the transition temperature, the degree of completion and the cooperative nature of the transition, which can be optimally designed when developing new spin-crossover materials.

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Recovery of copper from dilute cupric sulfate solution by electrodeposition method using boron-doped diamond electrodes

Natsui Keisuke, Yamaguchi Chizu, Einaga Yasuaki

Physica Status Solidi (A) Applications and Materials Science 2016

ISSN 1862-6300

The recovery of copper from wastewater is a key issue for environmental and economic aspects. The wastewater treatment containing copper ions has been carried out by various techniques. Among them, the electrodeposition is the "clean" method that is able to achieve the recovery of copper without requiring addition of chemicals and generating sludge or secondary wastes. However, the current efficiency would tend to decrease especially in a dilute solution, because hydrogen evolution and oxygen reduction reaction would occur as competition reaction. In this article, we study on the recovery of copper from dilute cupric sulfate solution as a model wastewater by an electrodeposition method using boron-doped diamond electrodes which have relatively higher hydrogen overpotential. Two types of boron-doped diamond electrodes were prepared with different boron doping level. The boron-doped diamond electrodes could achieve the recovery of copper with higher current efficiency because of inhibiting hydrogen evolution reaction, compared with glassy carbon electrode.

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Charge-Transfer Phase Transition of a Cyanide-Bridged Fe^II/Fe^III Coordination Polymer

Zhang Kuirun, Kang Soonchul, Yao Zi shuo, Nakamura Kazusa, Yamamoto Takashi, Einaga Yasuaki, Azuma Nobuaki, Miyazaki Yuji, Nakano Motohiro, Kanegawa Shinji, Sato Osamu

Angewandte Chemie - International Edition 2016

ISSN 1433-7851

Heterometallic Prussian blue analogues are known to exhibit thermally induced charge transfer, resulting in switching of optical and magnetic properties. However, charge-transfer phase transitions have not been reported for the simplest FeFe cyanide-bridged systems. A mixed-valence Fe^II/Fe^III cyanide-bridged coordination polymer, ([Fe(Tp)(CN)₃]₂Fe(bpe)5H₂O)_n, which demonstrates a thermally induced charge-transfer phase transition, is described. As a result of the charge transfer during this phase transition, the high-spin state of the whole system does not change to a low-spin state. This result is in contrast to FeCo cyanide-bridged systems that exhibit charge-transfer-induced spin transitions.

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Enhancement of the coercivity in Co-Ni layered double hydroxides by increasing basal spacing

Zhang Cuijuan, Tsuboi Tomoya, Namba Hiroaki, Einaga Yasuaki, Yamamoto Takashi

Dalton Transactions 45 ( 34 ) 13324 - 13331 2016

ISSN 1477-9226

The magnetic properties of layered double hydroxides (LDH) containing transition metal ions can still develop, compared with layered metal hydroxide salts which exhibit structure-dependent magnetism. In this article, we report the preparation of a hybrid magnet composed of Co-Ni LDH and n-alkylsulfonate anions (Co-Ni-CnSO₃ LDH). As Co-Ni LDH is anion-exchangeable, we can systematically control the interlayer spacing by intercalating n-alkylsulfonates with different carbon numbers. The magnetic properties were examined with temperature- and field-dependent magnetization measurements. As a result, we have revealed that the coercive field depends on the basal spacing. It is suggested that increasing the basal spacing varies the competition between the in-plane superexchange interactions and long-range out-of-plane dipolar interactions. Moreover, a jump in the coercive field at around 20 Å of the basal spacing is assumed to be the modification of the magnetic ordering in Co-Ni-CnSO₃ LDH.

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Selective production of methanol by the electrochemical reduction of CO₂ on boron-doped diamond electrodes in aqueous ammonia solution

Jiwanti Prastika K., Natsui Keisuke, Nakata Kazuya, Einaga Yasuaki

RSC Advances 6 ( 104 ) 102214 - 102217 2016

ISSN 2046-2069

The electrochemical reduction of CO₂ was investigated in an aqueous ammonia solution using boron-doped diamond electrodes. Methanol was mainly produced by reduction at a potential of -1.3 V (vs. Ag/AgCl) with a faradaic efficiency as high as 24.3%. Also, even in an aqueous ammonium bicarbonate solution (pH 7.9) without CO₂ bubbling, methanol was produced, while no methanol production was observed at higher (10.6) and lower pH (3.38). These observations suggest that the selectivity for methanol production in aqueous ammonia solutions is due to the electrochemical reduction of bicarbonate ions which are formed by the reaction between ammonia and CO₂. Moreover, we present the important role of ammonia as an electrolyte for the selective production of methanol by electrochemical reduction of CO₂.

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Fabrication of a Microfluidic Device with Boron-doped Diamond Electrodes for Electrochemical Analysis

Watanabe Takeshi, Shibano Shuhei, Maeda Hideto, Sugitani Ai, Katayama Michinobu, Matsumoto Yoshinori, Einaga Yasuaki

Electrochimica Acta 2015.09

ISSN 0013-4686

A prototype microfluidic device using boron-doped diamond (BDD) electrodes patterned on an alumina chip was designed and fabricated. Electrochemical microfluidic devices have advantages in that the amount of sample required is small, the measurement throughput is high, different functions can be integrated on a single device, and they are highly durable. In using the device for the flow injection analysis of oxalic acid, the application of a brief conditioning step ensured that the reproducibility of the current signal was excellent.Furthermore, the fabricated system also performed as a prototype of "elimination-detection flow system", in which interfering species are eliminated using "elimination electrodes" prior to the species reaching the "detection electrode". The fabricated device reduced the current due to interfering species by 78%. Designs of devices to improve this efficiency are also discussed.

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Novel Fe(II) spin crossover complexes involving a chalcogen-bond and π-stacking interactions with a paramagnetic and nonmagnetic M(dmit)<inf>2</inf> anion (M = Ni, Au; Dmit = 4,5-dithiolato-1,3-dithiole-2-thione)

Okai Mitsunobu, Takahashi Kazuyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki

Journal of Materials Chemistry C 3 ( 30 ) 7858 - 7864 2015.08

ISSN 2050-7534

To introduce both an inter-sulphur atom and π-stacking interaction between a spin crossover (SCO) cation and paramagnetic anion, we designed and synthesised two novel Fe(ii) SCO compounds involving a terpyridine-type thiazole containing ligand with the paramagnetic Ni(dmit)<inf>2</inf> and nonmagnetic Au(dmit)<inf>2</inf> anion (dmit = 4,5-dithiolato-1,3-dithiole-2-thione). The temperature variations of magnetic susceptibility and Mössbauer spectroscopy revealed that both complexes exhibited an almost complete SCO conversion, and moreover, the Ni(dmit)<inf>2</inf> anion was in a paramagnetic state down to 2 K. The crystal structures for the Ni(dmit)<inf>2</inf> complex at 213 and 400 K indicated that the chalcogen-bond and π-stacking interaction would be enhanced by the electrostatic interaction between the cation and anion, preventing the π-radicals from dimerising. The light-induced excited spin state trapping effect was observed at 5 K.

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Electrochemical behavior of zanamivir at gold-modified boron-doped diamond electrodes for an application in neuraminidase sensing

Wahyuni Wulan Tri, Ivandini Tribidasari A., Jiwanti Prastika K., Saepudin Endang, Gunlazuardi Jarnuzi, Einaga Yasuaki

Electrochemistry 83 ( 5 ) 357 - 362 2015.05

ISSN 1344-3542

This study emphasizes the electrochemical detection of Neuraminidase (NA) based on NA inhibition by Zanamivir. The detection method was developed based on the difference of electrochemical responses of Zanamivir in the presence and the absence of NA in phosphate buffer solution (pH 5.5). Gold and gold-modified boron-doped diamond was used as the working electrode and the measurement was conducted using cyclic voltammetry method. A linear calibration curve of Zanamivir was observed in the concentration range of 5 × 10^-6-1 × 10^-4 mol/L (R² = 0.991), with the estimated limit of detection (LOD) of 1.49 × 10^-6 mol/L. The presence of NA increases the peak current of gold oxidation and reduction with linear calibration curves were monitored in the concentration range of 0-15mU (R² = 0.996). An estimated LOD of 0.25mU NA and an excellent reproducibility of the detection with an RSD of 1.18% can be achieved. Application of a real sample was successfully demonstrated for NA detection in the presence of mucin, suggested that the method is promising for pharmaceutical or medical application.

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Crystal structure of 5,5′-dibromo-3,3′-di-tert-butyl-6,6′-dimethylbiphenyl-2,2′-diol

Obata Rika, Ohba Shigeru, Einaga Yasuaki, Nishiyama Shigeru, Stoeckli-Evans H.

Acta Crystallographica Section E: Structure Reports Online 71 ( 5 ) o278 - o279 2015.05

ISSN 1600-5368

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Anodic stripping voltammetry of gold nanoparticles at boron-doped diamond electrodes and its application in immunochromatographic strip tests

Ivandini Tribidasari A., Wicaksono Wiyogo P., Saepudin Endang, Rismetov Bakhadir, Einaga Yasuaki

Talanta 134 136 - 143 2015.03

ISSN 0039-9140

Anodic stripping voltammetry (ASV) of colloidal gold-nanoparticles (AuNPs) was investigated at boron-doped diamond (BDD) electrodes in 50 mM HClO₄. A deposition time of 300 s at-0.2 V (vs. Ag/AgCl) was fixed as the condition for the ASV. The voltammograms showed oxidation peaks that could be attributed to the oxidation of gold. These oxidation peaks were then investigated for potential application in immunochromatographic strip tests for the selective and quantitative detection of melamine, in which AuNPs were used as the label for the antibody of melamine. Linear regression of the oxidation peak currents appeared in the concentration range from 0.05-0.6 μg/mL melamine standard, with an estimated LOD of 0.069 μg/mL and an average relative standard deviation of 8.0%. This indicated that the method could be considered as an alternative method for selective and quantitative immunochromatographic applications. The validity was examined by the measurements of melamine injected into milk samples, which showed good recovery percentages during the measurements.

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Cathodic reductive coupling of methyl cinnamate on boron-doped diamond electrodes and synthesis of new neolignan-type products

Kojima Taiki, Obata Rika, Saito Tsuyoshi, Einaga Yasuaki, Nishiyama Shigeru

Beilstein Journal of Organic Chemistry 11 200 - 203 2015.02

ISSN 1860-5397

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Photochromism-induced amplification of critical current density in superconducting boron-doped diamond with an azobenzene molecular layer

Natsui Keisuke, Yamamoto Takashi, Akahori Miku, Einaga Yasuaki

ACS Applied Materials and Interfaces 7 ( 1 ) 887 - 894 2015.01

ISSN 1944-8244

A key issue in molecular electronics is the control of electronic states by optical stimuli, which enables fast and high-density data storage and temporal-spatial control over molecular processes. In this article, we report preparation of a photoswitchable superconductor using a heavily boron-doped diamond (BDD) with a photochromic azobenzene (AZ) molecular layer. BDDs electrode properties allow for electrochemical immobilization, followed by copper(I)-catalyzed alkyne-azide cycloaddition (a click reaction). Superconducting properties were examined with magnetic and electrical transport measurements, such as field-dependent isothermal magnetization, temperature-dependent resistance, and the low-temperature voltage-current response. These measurements revealed reversible amplification of the critical current density by 55% upon photoisomerization. This effect is explained as the reversible photoisomerization of AZ inducing an inhomogeneous electron distribution along the BDD surface that renormalizes the surface pinning contribution to the critical current.

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Electrochemical properties of phosphorus doped diamond

Mukuda Yu, Watanabe Takeshi, Ueda Akihiko, Nishibayashi Yoshiki, Einaga Yasuaki

Electrochimica Acta 179 599 - 603 2015.01

ISSN 0013-4686

The electrochemical properties of an n-type phosphorus doped diamond (PDD) electrode were investigated and compared with a p-type boron doped diamond (BDD) electrode. The Mott-Schottky plots in 0.1 M HClO₄ are reported and related to the energy band diagram of electrochemically pretreated BDD and PDD. These results revealed that the band position of anodically pretreated PDD corresponded to the one of anodically pretreated BDD. Moreover, it was found the flat-band potential of the anodically pretreated PDD decreased by ca. 1 V after cathodically pretreatment. The cyclic voltammetries for Ru(NH₃)₆
^3+/2+ showed that electrochemical behaviors of PDD and BDD were entirely different in possible direction for charge transfer across the electrode-electrolyte inaterface. In addition, less n-type diode-like behavior was observed at the cathodically pretreated PDD than the anodically pretreated PDD. These results point out the importance of the surface chemistry controlled by electrochemical pretreatments.

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Development of μtas for high-throughput screening of nad(p)-dependent oxidoreductases

Shimokihara Shota, Shitara Shunya, Oyobiki Ryo, Watanabe Takeshi, Einaga Yasuaki, Matsumoto Yoshinori, Fujiwara Kei, Horisawa Kenichi, Doi Nobuhide

1302 - 1304 2015

Antiferromagnetic transition in a novel star-shaped high-spin Fe(III) tetranuclear cluster from a mononuclear coordination anion featuring π-extended schiff base ligands

Takahashi Kazuyuki, Kawamukai Kiko, Mochida Tomoyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki, Mori Hatsumi, Shimura Yasuyuki, Sakakibara Toshiro, Fujisawa Takumi, Yamaguchi Akira, Sumiyama Akihiko

Chemistry Letters 44 ( 6 ) 840 - 842 2015

ISSN 0366-7022

A novel star-shaped high-spin Fe(III) tetranuclear cluster was unexpectedly obtained by the reaction of an [FeIII(phsal)<inf>2</inf>]- anion with an Fe(II) coordination cation (H<inf>2</inf>phsal: N-(2- hydroxyphenyl)salicylaldimine). Despite a star-shaped Fe(III) tetranuclear structure similar to reported Fe(III) single molecule magnets, the present compound exhibited a bulk antiferromagnetic transition at 0.6K due to a magnetic exchange coupling through intercluster π-stacking interactions.

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Advances in electrochemical biosensing using boron doped diamond microelectrode

Fierro Stéphane, Einaga Yasuaki

Topics in Applied Physics 121 295 - 318 2015

ISSN 0303-4216

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Yeast-based biochemical oxygen demand sensors using goldmodified boron-doped diamond electrodes

Ivandini Tribidasari A., Harmesa [No Value], Saepudin Endang, Einaga Yasuaki

Analytical Sciences 31 ( 7 ) 643 - 649 2015

ISSN 0910-6340

A gold nanoparticle modified boron-doped diamond electrode was developed as a transducer for biochemical oxygen demand (BOD) measurements. Rhodotorula mucilaginosa UICC Y-181 was immobilized in a sodium alginate matrix, and used as a biosensing agent. Cyclic voltammetry was applied to study the oxygen reduction reaction at the electrode, while amperometry was employed to detect oxygen, which was not consumed by the microorganisms. The optimum waiting time of 25 min was observed using 1-mm thickness of yeast film. A comparison against the system with free yeast cells shows less sensitivity of the current responses with a linear dynamic range (R2 = 0.99) of from 0.10 mM to 0.90 mM glucose (equivalent to 10 - 90 mg/L BOD) with an estimated limit of detection of 1.90 mg/L BOD. However, a better stability of the current responses could be achieved with an RSD of 3.35%. Moreover, less influence from the presence of copper ions was observed. The results indicate that the yeast-immobilized BOD sensors is more suitable to be applied in a real condition.

Magnetic enzymatic platform for organophosphate pesticide detection using boron-doped diamond electrodes

Pino Flavio, Ivandini Tribidasari A., Nakata Kazuya, Fujishima Akira, Merkoçi Arben, Einaga Yasuaki

Analytical Sciences 31 ( 10 ) 1061 - 1068 2015

ISSN 0910-6340

A simple and reliable enzymatic system for organophosporus pesticide detection was successfully developed, by exploiting the synergy between the magnetic beads collection capacity and the outstanding electrochemistry property of boron-doped diamond electrodes. The determination of an organophosphate pesticide, chlorpyrifos (CPF), was performed based on the inhibition system of the enzyme acetylcholinesterase bonded to magnetic beads through a biotin-streptavidin complex system. A better sensitivity was found for a system with magnetic beads in the concentration range of 10^-9 to 10^-5 M. The estimated limits of detection based on IC₁₀ (10% acetylcholinesterase (AChE) inhibition) have been detected and optimized to be 5.7 × 10^-10 M CPF. Spiked samples of water of Yokohama (Japan) have been measured to validate the efficiency of the enzymatic system. The results suggested that the use of magnetic beads to immobilize biomolecules or biosensing agents is suitable to maintain the superiority of BDD electrodes.

Toward high-throughput screening of NAD(P)-dependent oxidoreductases using boron-doped diamond microelectrodes and microfluidic devices

Oyobiki Ryo, Kato Taisuke, Katayama Michinobu, Sugitani Ai, Watanabe Takeshi, Einaga Yasuaki, Matsumoto Yoshinori, Horisawa Kenichi, Doi Nobuhide

Analytical Chemistry 86 ( 19 ) 9570 - 9575 2014.10

ISSN 0003-2700

Although oxidoreductases are widely used in many applications, such as biosensors and biofuel cells, improvements in the function of existing oxidoreductases or the discovery of novel oxidoreductases with greater activities is desired. To increase the activity of oxidoreductases by directed evolution, a powerful screening technique for oxidoreductases is required. In this study, we demonstrate the utility of boron-doped diamond (BDD) microelectrodes for quantitative and potentially high-throughput measurement of the activity of NAD(P)-dependent oxidoreductases. We first confirmed that BDD microelectrodes can quantify the activity of low concentrations (10-100 pM) of glucose-6-phosphate dehydrogenase and alcohol dehydrogenase with a measuring time of 1 ms per sample. In addition, we found that poisoning of BDD microelectrodes can be repressed by optimizing the pH and by adding l-arginine to the enzyme solution as an antiaggregation agent. Finally, we fabricated a microfluidic device containing a BDD electrode for the first time and observed the elevation of the oxidation current of NADH with increasing flow rate. These results imply that the combination of a BDD microelectrode and microfluidics can be used for high-throughput screening of an oxidoreductase library containing a large number (>10⁶) of samples, each with a small (nanoliter) sample volume.

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A double-QM/MM method for investigating donor-acceptor electron-transfer reactions in solution

Futera Zdenek, Sodeyama Keitaro, Burda Jaroslav V., Einaga Yasuaki, Tateyama Yoshitaka

Physical Chemistry Chemical Physics 16 ( 36 ) 19530 - 19539 2014.09

ISSN 1463-9076

We developed a double-quantum mechanical/molecular mechanical (d-QM/MM) method for investigation of full outer-sphere electron transfer (ET) processes between a donor and an acceptor (DA) in condensed matter. In the d-QM/MM method, which employs the novel concept of multiple QM regions, one can easily specify the number of electrons, spin states and appropriate exchange-correlation treatment in each QM region, which is especially important in the cases of ET involving transition metal sites. We investigated Fe^2+/3+ self-exchange and Fe³⁺ + Ru²⁺ → Fe²⁺ + Ru³⁺ in aqueous solution as model reactions, and demonstrated that the d-QM/MM method gives reasonable accuracy for the redox potential, reorganization free energy and electronic coupling. In particular, the DA distance dependencies of those quantities are clearly shown at the density functional theory hybrid functional level. The present d-QM/MM method allows us to explore the intermediate DA distance region, important for long-range ET phenomena observed in electrochemistry (on the solid-liquid interfaces) and biochemistry, which cannot be dealt by the half-reaction scheme with the conventional QM/MM. © 2014 The Owner Societies.

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First principles calculation study on surfaces and water interfaces of boron-doped diamond

Futera Zdenek, Watanabe Takeshi, Einaga Yasuaki, Tateyama Yoshitaka

Journal of Physical Chemistry C 118 ( 38 ) 22040 - 22052 2014.09

ISSN 1932-7447

We investigated water interfaces of boron-doped diamond (BDD) terminated by hydrogen, oxygen, and hydroxyl groups by using density functional theory (DFT)-based molecular dynamics to elucidate the electrochemical behaviors of the as-grown and oxidized BDD electrodes. The reversible outer-sphere electron transfer on the as-grown electrode and the irreversibility on the oxidized electrode, observed in the experiment, are well explained by the BDD band position and subsurface band bending, which depend on the termination and interfacial dipoles. The reductive character of the H-terminated BDD is found, while the interface covered by the carbonyl oxygen is clearly oxidative. The redox character of the hydroxyl termination depends on the lateral hydrogen bonding network among the termination groups and is rather oxidative at the water interface. We also examined the preference of the boron position in the diamond and the stability of boron pairs and clusters. It is suggested that the wide distribution of the single boron dopants is crucial to the BDD conductivity, against the tendency of clustering. These results give novel atomistic aspects of the termination and the boron doping effects on the BDD electrodes, which is useful for further exploration of the efficient electrochemical applications of BDD.

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Direct determination of chemical oxygen demand by anodic decomposition of organic compounds at a diamond electrode

Kondo Takeshi, Tamura Yusuke, Hoshino Masaki, Watanabe Takeshi, Aikawa Tatsuo, Yuasa Makoto, Einaga Yasuaki

Analytical Chemistry 86 ( 16 ) 8066 - 8072 2014.08

ISSN 0003-2700

Chemical oxygen demand (COD) was measured directly with a simple electrochemical method using a boron-doped diamond (BDD) electrode. By applying a highly positive potential (+2.5 V vs Ag/AgCl) to an aqueous electrolyte containing potassium hydrogen phthalate, glucose, and lactic acid or sodium dodecylbenzenesulfonate using a BDD electrode, an anodic current corresponding to the electrolytic decomposition of these organic compounds was observed. No such current was seen on glassy carbon or platinum electrodes due to a significant background current caused by the oxygen evolution reaction. The electric charge for the anodic current observed at the BDD electrode was found to be consistent with the theoretical charge required for the electrolytic decomposition of the organic compounds to CO₂ and was used to calculate COD. This analysis was performed by a simple I-t measurement at constant potential using a BDD electrode, and no calibration was needed. This new simple indicator, "ECOD" (electrochemical oxygen demand), will be useful for continuous monitoring of industrial wastewater with low protein concentrations and on-site instant analysis of natural water with a BDD electrode-based portable ECOD meter. © 2014 American Chemical Society.

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Electrochemical Application of Diamond Electrodes

Einaga Yasuaki

493 - 512 2014.03

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Synergistic spin transition between spin crossover and spin-peierls-like singlet formation in the halogen-bonded molecular hybrid system

Fukuroi Kappei, Takahashi Kazuyuki, Mochida Tomoyuki, Sakurai Takahiro, Ohta Hitoshi, Yamamoto Takashi, Einaga Yasuaki, Mori Hatsumi

Angewandte Chemie - International Edition 53 ( 7 ) 1983 - 1986 2014.02

ISSN 1433-7851

To introduce halogen-bond interactions between a cation and an anion, a novel Fe^III complex from iodine-substituted ligands involving a paramagnetic nickel dithiolene anion was prepared and characterized. The compound exhibited the synergy between a spin-crossover transition and a spin-Peierls-like singlet formation. The halogen-bond interactions between the iodine and the sulfur atoms stabilized the paramagnetic state of π-spins and played a crucial role in the synergistic magnetic transition between d- and π-spins. In addition, the compound showed the light-induced excited spin state trapping effect. Something to get crossover: An Fe^III complex with iodine-substituted ligands involving a paramagnetic nickel dithiolene anion shows a synergy between a spin-crossover transition and a spin-Peierls-like singlet formation. The halogen-bond interactions between the iodine and the sulfur atoms stabilized the paramagnetic state of π-spins and played a significant role in the synergistic magnetic transition between d- and π-spins. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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High-yield electrochemical production of formaldehyde from CO₂ and seawater

Nakata Kazuya, Ozaki Takuya, Terashima Chiaki, Fujishima Akira, Einaga Yasuaki

Angewandte Chemie - International Edition 53 ( 3 ) 871 - 874 2014

ISSN 1433-7851

The catalytic, electrocatalytic, or photocatalytic conversion of CO ₂ into useful chemicals in high yield for industrial applications has so far proven difficult. Herein, we present our work on the electrochemical reduction of CO₂ in seawater using a boron-doped diamond (BDD) electrode under ambient conditions to produce formaldehyde. This method overcomes the usual limitation of the low yield of higher-order products, and also reduces the generation of H₂. In comparison with other electrode materials, BDD electrodes have a wide potential window and high electrochemical stability, and, moreover, exhibit very high Faradaic efficiency (74 %) for the production of formaldehyde, using either methanol, aqueous NaCl, or seawater as the electrolyte. The high Faradaic efficiency is attributed to the sp ³-bonded carbon of the BDD. Our results have wide ranging implications for the efficient and cost-effective conversion of CO₂. Boron is a diamond's best friend: A boron-doped diamond (BDD) electrode exhibited very high Faradaic efficiency (74 %) for the production of formaldehyde using either methanol, aqueous NaCl, or seawater as the electrolyte at room temperature and ambient pressure. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Diamond electrodes

Einaga Yasuaki, Foord John S., Swain Greg M.

MRS Bulletin 39 ( 6 ) 525 - 532 2014

ISSN 0883-7694

Boron-doped diamond electrodes have attracted increasing interest from researchers due to their outstanding properties for electroanalysis and other electrochemical applications. Material quality and availability have come a long way since the initial reports on the basic electrochemical properties back in the late 1980s and early 1990s. In this review, we highlight how diamond electrochemistry has diversified and matured in recent years in terms of the understanding of structure-property relationships and the development of new applications of materials in electroanalytical chemistry. © Materials Research Society 2014.

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Synthesis of biodiesel using a two-compartments electrochemical cell

Shibano Shuhei, Ivandini Tribidasari A., Terashima Chiaki, Nakata Kazuya, Einaga Yasuaki

Chemistry Letters 43 ( 8 ) 1292 - 1293 2014

ISSN 0366-7022

An electrochemical method was developed for biodiesel, i.e., fatty acid methyl ester (FAME), production. A twocompartment cell completed with a cation-exchange separating membrane was utilized to minimize recombination between protons and hydroxide or methoxide ions, which leads to the low product yield. In addition to the product yield increase, the method was found to reduce the requirement of organic salt to be only in the cathode chamber. Electrolysis at low voltage (4.6 V) resulting high product yield (ca. 94% in 2 h) at Pt as well as a boron-doped diamond (BDD) electrode as the cathode, suggested the system was free from the dependence on electrode types.

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Tailored design of boron-doped diamond electrodes for various electrochemical applications with boron-doping level and sp²-bonded carbon impurities

Watanabe Takeshi, Honda Yuki, Kanda Kazuhiro, Einaga Yasuaki

Physica Status Solidi (A) Applications and Materials Science 211 ( 12 ) 2709 - 2717 2014

ISSN 1862-6300

The effects of sp2-bonded carbon impurities on the electrochemical properties of boron-doped diamond were investigated in moderately ([B] < 10²⁰cm^-3) and heavily ([B] > 10²¹cm^-3) boron doping levels. Significant influences of sp2-bonded carbon impurities, which show glassy carbon-like electrochemical properties after anodic oxidation, were observed in heavily boron-doped diamond. This indicated that the significant effects of enhanced adsorption properties were possibly caused by surface relaxation of the strains induced by heavy boron doping and sp²-bonded carbon impurities. On the other hand, their durability was still similar to diamond electrodes rather than glassy-carbon electrodes because of the low fraction of sp²-bonded carbon impurities. Such "active" diamond electrodes are much less suitable for wastewater treatment than ordinary diamond electrodes due to a different oxygenevolution mechanism. On the other hand, "active" BDD electrodes have a much higher efficiency for electrochemical ozone production than other BDD electrodes. The electrode properties of BDD can be designed by controlling the boron doping level and introducing the sp²-bonded carbon impurities. The guidelines proposed in this study can be used effectively to design electrodes according to their individual application, such as for use as electrochemical sensors, in wastewater treatment or electrochemical ozone production.

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Electrochemical detection of hydrogen peroxide at platinum-modified diamond electrodes for an application in melamine strip tests

Rismetov Bakhadir, Ivandini Tribidasari A., Saepudin Endang, Einaga Yasuaki

Diamond and Related Materials 48 88 - 95 2014

ISSN 0925-9635

Electrochemical detection of hydrogen peroxide (H₂O₂) at a platinum-deposited boron doped diamond was studied for an application in melamine strip test. Deposition of Pt particles at a boron-doped diamond surface was performed using cyclic voltammetry method. The method was also used for electrochemical measurements. The oxidation-reduction peak currents of H ₂O₂ at + 0.6 V and - 0.1 V (vs. Ag/AgCl), respectively were found to be linear in the concentration range of 0.05-20 mM (R² = 0.99). Linearity was also observed to be dependent on horseradish peroxidase (HRP) concentration in the constant concentration of H₂O₂. The method was then applied in immunochromatographic strip test for melamine detection to determine the activity of HRP labeled at melamine antibody. Taking an assumption that the activity of HRP was equivalent to melamine concentration, linearity of the current responses to the concentrations of standard melamine solutions in the range of 5-100 μg/ml could be achieved. Limit of detection of 0.51 μg/ml was estimated. The obtained results demonstrated that the designed biosensor for detection of H₂O₂ could be applied for the quantitative and selective detection of melamine. © 2014 Elsevier B.V.

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Cathodic pretreatment improves the resistance of boron-doped diamond electrodes to dopamine fouling

Trouillon Raphaël, Einaga Yasuaki, Gijs Martin A M

Electrochemistry Communications 47 92 - 95 2014

ISSN 1388-2481

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Fabrication of boron doped diamond chip electrodes for single drop analysis

Sugitani Ai, Katayama Michinobu, Watanabe Takeshi, Matsumoto Yoshinori, Einaga Yasuaki

RSC Advances 3 ( 48 ) 25636 - 25639 2013.12

As a prototype for a "highly sensitive electrochemical detection system for single drop analysis using boron-doped diamond (BDD) electrodes", a three-electrode system for the measurement of samples consisting of a single drop was fabricated. An Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) system, employing the Bosch process in order to realize high-aspect-ratio near vertical structures, was used to etch the BDD. A single drop (10 μL) was analyzed using the resulting fabricated 'BDD chip electrode' which exhibited the typical superior electrochemical properties of BDD electrodes. © 2013 The Royal Society of Chemistry.

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Structure-distortion-induced photomagnetic effect in azobenzene/ polyoxometalate Langmuir-Blodgett films

Yamamoto Takashi, Umemura Yasushi, Einaga Yasuaki

Dalton Transactions 42 ( 45 ) 16014 - 16020 2013.12

ISSN 1477-9226

We have prepared photomagnetic Langmuir-Blodgett films composed of an amphiphilic azobenzene and a magnetic polyoxometalate. The obtained film possesses a well-organized layered structure where polyoxometalate anions are sandwiched by azobenzene cations in a single-layered manner. Reversible photoisomerization of azobenzene was achieved even at low temperature, accompanying intensity changes in the d-d transition of polyoxometalate anions. The photomagnetic effect was observed reversibly upon alternate UV and visible light irradiation. Based on polarized spectroscopy, the observed photomagnetic effect is ascribed to the structure-distortion of polyoxometalate layers. © 2013 The Royal Society of Chemistry.

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A neutral Fe(iii) compound exhibiting a two-step spin transition and dielectric anomalies

Li Zhao Yang, Dai Jing Wei, Gagnon Kevin J., Cai Hong Ling, Yamamoto Takashi, Einaga Yasuaki, Zhao Han Hua, Kanegawa Shinji, Sato Osamu, Dunbar Kim R., Xiong Ren Gen

Dalton Transactions 42 ( 41 ) 14685 - 14688 2013.11

ISSN 1477-9226

The mononuclear ferric compound Fe(H-5-Cl-thsa-Me)(5-Cl-thsa-Me) ·H₂O (1) was synthesized and characterized using powder/single-crystal X-ray diffraction, Mössbauer spectroscopy, differential scanning calorimetry (DSC), and magnetic susceptibility measurements. This photo-responsive compound shows reversible, two-step spin-crossover behaviour. Moreover, dielectric anomalies were observed during the spin transitions, demonstrating the multifunctional properties of compound 1. © 2013 The Royal Society of Chemistry.

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Modulation of critical current density in polycrystalline boron-doped diamond by surface modification

Natsui Keisuke, Yamamoto Takashi, Watanabe Takeshi, Kamihara Yoichi, Einaga Yasuaki

Physica Status Solidi (B) Basic Research 250 ( 9 ) 1943 - 1949 2013.09

ISSN 0370-1972

The maximum current flowed with zero resistance, referred to the critical current density, is desired to be sufficiently large in order to apply superconducting wire rods and electromagnets to various devices. Although the critical current density can be enhanced by introduction of non-superconducting impurities, the transition temperature would become diminished in such a case. Here, we report modulation of a critical current density in heavily boron-doped diamonds (BDDs) by changing the surface-termination without introducing any impurity. The surface of a BDD was changed between hydrogen- and oxygen-termination. As a result, the critical current density could be modulated in a reversible manner between the hydrogen- and oxygen-terminated diamonds with maintenance of the superconducting transition temperature. This is because the volume fractions of the superconducting phases were modulated by surface modification. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Application of boron-doped diamond microelectrodes for dental treatment with pinpoint ozone-water production

Ochiai Tsuyoshi, Ishii Yuya, Tago Shoko, Hara Masayuki, Sato Takuya, Hirota Kazuo, Nakata Kazuya, Murakami Taketoshi, Einaga Yasuaki, Fujishima Akira

ChemPhysChem 14 ( 10 ) 2094 - 2096 2013.07

ISSN 1439-4235

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Influence of supporting electrolyte on the electrochemical oxidation of formic acid on boron-doped diamond electrodes

Fierro Stéphane, Honda Yuki, Einaga Yasuaki

Bulletin of the Chemical Society of Japan 86 ( 6 ) 749 - 754 2013.06

ISSN 0009-2673

The influence of support electrolyte on the electrochemical degradation of formic acid was studied on boron-doped diamond (BDD) electrodes. Experimental data are compared with a theoretical model, which is based on organic degradation via hydroxyl radicals under current or mass transport controlled regimes depending on the difference between the applied and limiting current. The kinetics of the different reactions involved in the process is also briefly studied. It is shown that when sulfuric acid is used as support electrolyte, the reactions involving electro-generated peroxodisulfate anions during the degradation of formic acid are highly dependent on temperature. For this reason, the influence on the overall process of the chemical reaction between these anions and formic acid tends to increase with increasing temperatures and when the electrolysis becomes controlled by mass transport. However, it is proven that degradation of formic acid in the bulk occurs under current controlled regime as well. Furthermore, it is shown that the use of sulfuric acid as support electrolyte enhances the degradation of formic acid at high temperatures and when the process is controlled by mass transfer compared to other inert support electrolytes. © 2013 The Chemical Society of Japan.

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Development of electrolyte-free ozone sensors using boron-doped diamond electrodes

Ishii Yuya, Ivandini Tribidasari A., Murata Kazutaka, Einaga Yasuaki

Analytical Chemistry 85 ( 9 ) 4284 - 4288 2013.05

ISSN 0003-2700

The electrochemical detection of dissolved ozone in water was examined using boron-doped diamond (BDD) electrodes. A well-defined reduction peak was observed at ∼380 mV for H-terminated BDD, whereas it was observed at ∼200 mV in the case of O-terminated BDD for an ozone solution in a 0.1 M phosphate buffer solution at pH 7. The peak potential for ozone reduction was selective with respect to oxygen reduction at both H- and O-terminated BDD electrodes, whereas it occurred at approximately the same potential as oxygen reduction at other types of solid electrodes, including glassy-carbon, platinum, and gold electrodes. Interference from chlorine was not observed in lower concentration than 300 μM ClO^-. Furthermore, in order to apply the detection technique to electrolyte-free media, BDD microelectrodes were also used. A linear calibration curve for dissolved ozone in water could be achieved between concentrations of 0.49 and 740 μM, with an estimated detection limit (S/N = 3) of 0.185 μM (S/N = 3). Excellent stability was demonstrated for repetitions of these calibration curves performed in 3 consecutive days. © 2013 American Chemical Society.

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Electrochemical detection of lipophilic antioxidants with high sensitivity at boron-doped diamond electrode

Kondo Takeshi, Sakai Kazuya, Watanabe Takeshi, Einaga Yasuaki, Yuasa Makoto

Electrochimica Acta 95 205 - 211 2013.04

ISSN 0013-4686

The electrochemical detection of lipophilic antioxidants, α-tocopherol (vitamin E, VE) and ubiquinone (coenzyme Q₁₀, CoQ₁₀), in methanol and in methanol/hexane mixture solutions, respectively, at boron-doped diamond (BDD) electrodes was investigated by cyclic voltammetry (CV) and flow-injection electrochemical measurements. CV measurements revealed that the overpotential for electrochemical reaction of VE and CoQ₁₀ was larger at an oxidized BDD electrode surface than at that of a hydrogenated BDD (H-BDD) electrode. The slope of the CV calibration curve used to determine the VE and CoQ₁₀ concentrations was larger at a glassy carbon (GC) electrode than at the H-BDD electrode; however, the signal-to-background ratio was larger at the H-BDD electrode than at the GC electrode, due to the low background feature of the H-BDD electrode. The limit of detection (LOD), defined by a signal-to-noise ratio of three for flow-injection electrochemical detection, was much smaller at the H-BDD electrode (VE: 41 nM and CoQ₁₀: 17 nM) than at the GC electrode (VE: 263 nM and CoQ₁₀: 71 nM). These results confirm that the H-BDD electrode is reliable for the electrochemical detection of lipophilic antioxidants, especially at low concentrations. © 2013 Elsevier Ltd. All rights reserved.

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Simultaneous detection of iodine and iodide on boron doped diamond electrodes

Fierro Stéphane, Comninellis Christos, Einaga Yasuaki

Talanta 103 33 - 37 2013.01

ISSN 0039-9140

Individual and simultaneous electrochemical detection of iodide and iodine has been performed via cyclic voltammetry on boron doped diamond (BDD) electrodes in a 1 M NaClO₄ (pH 8) solution, representative of typical environmental water conditions. It is feasible to compute accurate calibration curve for both compounds using cyclic voltammetry measurements by determining the peak current intensities as a function of the concentration. A lower detection limit of about 20 μM was obtained for iodide and 10 μM for iodine. Based on the comparison between the peak current intensities reported during the oxidation of KI, it is probable that iodide (I^-) is ?rst oxidized in a single step to yield iodine (I₂). The latter is further oxidized to obtain IO₃
^-. This technique, however, did not allow for a reasonably accurate detection of iodate (IO₃ ^-) on a BDD electrode. © 2012 Elsevier B.V. All rights reserved.

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Controlling the diffusion profile of electroactive species for selective anodic stripping voltammetry of cadmium at boron-doped diamond electrodes

Sugitani Ai, Watanabe Takeshi, Ivandini Tribidasari A., Iguchi Tatsuo, Einaga Yasuaki

Physical Chemistry Chemical Physics 15 ( 1 ) 142 - 147 2013.01

ISSN 1463-9076

Selective anodic stripping voltammetry of trace metal ions in a mixture solution with another interfering metal was developed based on Fick's law concerning the diffusion profile of interfering metals at the electrode surface after electrolysis treatment. A boron-doped diamond film was used as the sensing electrode, while a perforated carbon sheet was used for the interference-depleting electrode. The influence of the electrode distance and the time of electrolysis on the formation of the diffusion profile was studied. As a working model, the detection of cadmium with copper interference was investigated. The advantage of the method in comparison to general electrolysis was also discussed. The method offers a new perspective for improving the selective detection of metal ions by analyzing the diffusion profiles of the interfering species at the surface of electrodes. © the Owner Societies 2013.

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Electrochemical Detection of Selenium (IV) and (VI) at Gold-Modified Diamond Electrodes

Ivandini Tribidasari A., Einaga Yasuaki

Electrocatalysis 4 ( 4 ) 367 - 374 2013

ISSN 1868-2529

Electrochemical detection of Se (IV) and (VI) was investigated at gold-modified boron-doped diamond electrodes. Cyclic voltammetry in acid condition showed that the onset of current flows of Se (IV) and Se (VI) occurred at almost similar potentials. Furthermore, the currents at the peak potential of ∼0.9 V (vs. Ag/AgCl) showed high linearity against concentrations of both Se (IV) and Se (VI) with estimated limits of detection (S/N = 3) of 20 and 50 ppb, respectively. However, whereas oxidation peaks of Se (IV) and Se (VI) can be observed in acid and neutral pH, only oxidation peak of Se (IV) appeared in high pH. The possibility to differentiate a mixture of Se (IV) and Se (VI) by applying cyclic voltammogram (CV) at acidic and basic conditions was discussed, and it was promising, especially because, previously, it always stated that Se (VI) was not electrochemically active. © 2013 Springer Science+Business Media New York.

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In vivo pH monitoring using boron doped diamond microelectrode and silver needles

Fierro Stéphane, Seishima Ryo, Nagano Osamu, Saya Hideyuki, Einaga Yasuaki

Scientific Reports 3 2013

This study presents the in vivo electrochemical monitoring of pH using boron doped diamond (BDD) microelectrode and silver needles for potential application in medical diagnosis. Accurate calibration curve for pH determination were obtained through in vitro electrochemical measurements. The increase induced in stomach pH by treatment with pantoprazole was used to demonstrate that it is possible to monitor the pH in vivo using the simple and noninvasive system proposed herein. Using the results of the in vivo and in vitro experiments, a quantitative analysis of the increase in stomach pH is also presented. It is proposed that the catheter-free pH monitoring system presented in this study could be potentially employed in any biological environment.

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Development of a biochemical oxygen demand sensor using gold-modified boron doped diamond electrodes

Ivandini Tribidasari A., Saepudin Endang, Wardah Habibah, Harmesa [No Value], Dewangga Netra, Einaga Yasuaki

Analytical Chemistry 84 ( 22 ) 9825 - 9832 2012.11

ISSN 0003-2700

Gold-modified boron doped diamond (BDD) electrodes were examined for the amperometric detection of oxygen as well as a detector for measuring biochemical oxygen demand (BOD) using Rhodotorula mucilaginosa UICC Y-181. An optimum potential of -0.5 V (vs Ag/AgCl) was applied, and the optimum waiting time was observed to be 20 min. A linear calibration curve for oxygen reduction was achieved with a sensitivity of 1.4 μA mg^-1 L oxygen. Furthermore, a linear calibration curve in the glucose concentration range of 0.1-0.5 mM (equivalent to 10-50 mg L^-1 BOD) was obtained with an estimated detection limit of 4 mg L^-1 BOD. Excellent reproducibility of the BOD sensor was shown with an RSD of 0.9%. Moreover, the BOD sensor showed good tolerance against the presence of copper ions up to a maximum concentration of 0.80 μM (equivalent to 50 ppb). The sensor was applied to BOD measurements of the water from a lake at the University of Indonesia in Jakarta, Indonesia, with results comparable to those made using a standard method for BOD measurement. © 2012 American Chemical Society.

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Highly sensitive detection of Cr ⁶⁺ on boron doped diamond electrodes

Fierro Stéphane, Watanabe Takeshi, Akai Kazumi, Einaga Yasuaki

Electrochimica Acta 82 9 - 11 2012.11

ISSN 0013-4686

Electrochemical detection of Cr ⁶⁺ has been performed by cyclic and linear scan voltammetry on boron doped diamond (BDD) electrode. This method is based on the electrochemical reduction of Cr ⁶⁺ to Cr ³⁺. The resulting voltammograms exhibited a clear peak at 0.03 V vs. AgCl related to this reduction and highly accurate (r ² = 0.99) calibration curves could be obtained for a chromium concentration range between 10 ppb and 5 ppm. The influence of other metals dissolved in solution (Cu, Cd, Pb, B and Se) has been investigated as well and it was found that the Cr ⁶⁺ calibration curves remained unaltered. For all the experiments performed, a detection limit around 3 ppb was achieved. The high accuracy and reproducibility of the results as well as the excellent stability of the electrode material proves the excellent capabilities of this system for chromium detection. © 2012 Elsevier Ltd.

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Paramagnetic phase of a heavy-fermion compound, CeFePO, probed by< ⁵⁷Fe mössbauer spectroscopy

Nakamura Tetsur, Yamamoto Takash, Matoba Masanor, Einaga Yasuak, Kamihara Yoich

Journal of the Physical Society of Japan 81 ( 6 ) 2012.06

ISSN 0031-9015

⁵⁷Fe Mössbauer spectroscopy was applied to an iron-based layered compound CeFePO. At temperatures from 9.4 to 293 K, no magnetic splitting was observed in the Mössbauer spectra of CeFePO indicating a paramagnetic phase of the Fe magnetic sublattice. All the spectra were fitted with a small quadrupole splitting, and the Debye temperature of CeFePO was found to be ∼448 K. The isomer shift at room temperature, 0.32 mm/s, was almost equal to those of LnFeAsO (Ln = La, Ce, Sm). Comparing s-electron density using the isomer shifts and unit cell volumes, it was found that the Fe of CeFePO has a similar valence state to other layered iron-based quaternary oxypnictides except LaFePO. © 2012 The Physical Society of Japan.

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Anodic oxidation on a boron-doped diamond electrode mediated by methoxy radicals

Sumi Takenori, Saitoh Tsuyoshi, Natsui Keisuke, Yamamoto Takashi, Atobe Mahito, Einaga Yasuaki, Nishiyama Shigeru

Angewandte Chemie - International Edition 51 ( 22 ) 5443 - 5446 2012.05

ISSN 1433-7851

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Cooperative spin transition and thermally quenched high-spin state in new polymorph of [Fe(qsal) ₂]I ₃

Takahashi Kazuyuki, Sato Tetsuya, Mori Hatsumi, Tajima Hiroyuki, Einaga Yasuaki, Sato Osamu

Hyperfine Interactions 206 ( 1-3 ) 1 - 5 2012.03

ISSN 0304-3843

Novel polymorph of the ferric spin crossover complex, β-[Fe(qsal) ₂]I ₃ [qsalH = N-(8-quinolyl)salicylaldimine], has been prepared and characterized by magnetic susceptibilities and Mössbauer spectra. β polymorph exhibited a cooperative complete spin transition with a thermal hysteresis of 25 K and a tendency to be quenched in the high-spin (HS) state, which is contrastive to a gradual incomplete spin conversion in α polymorph. © 2011 Springer Science+Business Media B.V.

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Anodic Oxidation on a Boron-Doped Diamond Electrode Mediated by Methoxy Radicals.

EINAGA YASUAKI

Angew. Chem. Int. Ed. 2012

Research paper (scientific journal), Single Work

Dopamine detection on boron-doped diamond electrodes using fast cyclic voltammetry

Kato Taisuke, Fierro Stéphane, Watanabe Takeshi, Yoshimi Kenji, Einaga Yasuaki

Chemistry Letters 41 ( 3 ) 224 - 226 2012

ISSN 0366-7022

A new method is proposed for the accurate and reproducible detection of dopamine using cyclic voltammetry on boron-doped diamond (BDD) electrode. It is shown that reproducible voltammograms can be obtained when applying a relatively high scan rate (100Vs ^-1) during the detection measurements. For lower scan rates (1Vs ^-1), it is proven that electrode fouling occurs due do the deposition of a polymer at the electrode surface arising from the oxidation of aminochrome. Cyclic voltammetry measurements of the [Fe(CN) ₆] ^3-/[Fe(CN) ₆] ^4- couple performed before and after dopamine detection on BDD and glassy carbon electrodes have shown that the electrochemical activity of the electrode decreases only at low scan rates for BDD dopamine (DA) detection, which leads to electrode poisoning whereas the activity remains unchanged for higher scan rates. However, on glassy carbon electrodes, the electrochemical activity of the material decreases after DA detection measurements independently of the scan rate applied. Therefore, this study shows that electrode fouling during the detection of dopamine by cyclic voltammetry can be avoided only when using BDD electrode but also only for high applied scan rates. © 2012 The Chemical Society of Japan.

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In vivo assessment of cancerous tumors using boron doped diamond microelectrode

Fierro Stéphane, Yoshikawa Momoko, Nagano Osamu, Yoshimi Kenji, Saya Hideyuki, Einaga Yasuaki

Scientific Reports 2 2012

The in vitro and in vivo electrochemical detection of the reduced form of glutathione (L-γ-glutamyl-L-cysteinyl-glycine, GSH) using boron doped diamond (BDD) microelectrode for potential application in the assessment of cancerous tumors is presented. Accurate calibration curve for the determination of GSH could be obtained by the in vitro electrochemical measurements. Additionally, it was shown that it was possible to separate the detection of GSH from the oxidized form of glutathione (GSSG) using chronoamperometry measurements. In vivo GSH detection measurements have been performed in human cancer cells inoculated in immunodeficient mice. These measurements have shown that the difference of GSH level between cancerous and normal tissues can be detected. Moreover, GSH detection measurements carried out before and after X-ray irradiation have proved that it is possible to assess in vivo the decrease in GSH concentration in the tumor after a specific treatment.

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PH sensing using boron doped diamond electrodes

Fierro Stéphane, Mitani Naoko, Comninellis Christos, Einaga Yasuaki

Physical Chemistry Chemical Physics 13 ( 37 ) 16795 - 16799 2011.10

ISSN 1463-9076

The boron doped diamond (BDD) electrode is presented as an appropriate candidate for next generation glass-free, highly stable and accurate pH sensors. The method used in this study is based on the potential change related to the hydrogen evolution reaction following a current step, which is pH dependent. Alkali cations in the solution have no influence on the accuracy of the pH calibration curve, which provides an advantage with respect to the conventional pH glass electrode. The unwanted influence of electrochemically active compounds in solution can be avoided by adjusting the current density applied during chronopotentiometric measurements. The accuracy of the pH measurements is due to the excellent stability as well as the wide potential window and low background current of BDD electrodes. This faculty was not observed when using conventional electrode materials. The efficacy of this new type of pH sensor has been tested using tap water as a typical real sample. © 2011 The Owner Societies.

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Phasic reward responses in the monkey striatum as detected by voltammetry with diamond microelectrodes

Yoshimi Kenji, Naya Yuuki, Mitani Naoko, Kato Taisuke, Inoue Masato, Natori Shihoko, Takahashi Toshimitu, Weitemier Adam, Nishikawa Natsuko, McHugh Thomas, Einaga Yasuaki, Kitazawa Shigeru

Neuroscience Research 71 ( 1 ) 49 - 62 2011.09

ISSN 0168-0102

Reward-induced burst firing of dopaminergic neurons has mainly been studied in the primate midbrain. Voltammetry allows high-speed detection of dopamine release in the projection area. Although voltammetry has revealed presynaptic modulation of dopamine release in the striatum, to date, reward-induced release in awakened brains has been recorded only in rodents. To make such recordings, it is possible to use conventional carbon fibres in monkey brains but the use of these fibres is limited by their physical fragility. In this study, constant-potential amperometry was applied to novel diamond microelectrodes for high-speed detection of dopamine. In primate brains during Pavlovian cue-reward trials, a sharp response to a reward cue was detected in the caudate of Japanese monkeys. Overall, this method allows measurements of monoamine release in specific target areas of large brains, the findings from which will expand the knowledge of reward responses obtained by unit recordings. © 2011 Elsevier Ireland Ltd and the Japan Neuroscience Society.

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Applications of Polycrystalline and Modified Functional Diamond Electrodes

Einaga Yasuaki, Fujishima Akira

109 - 131 2011.06

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Erratum

Ivandini Tribidasari A., Yamada Daisuke, Watanabe Takeshi, Matsuura Hiroaki, Nakano Nabuo, Fujishima Akira, Einaga Yasuaki

Journal of Electroanalytical Chemistry 655 ( 1 ) 96 2011.05

ISSN 1572-6657

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Electronic conductivity in Berlin green and Prussian blue

Pajerowski Daniel M., Watanabe Takeshi, Yamamoto Takashi, Einaga Yasuaki

Physical Review B - Condensed Matter and Materials Physics 83 ( 15 ) 2011.04

ISSN 1098-0121

We report the temperature dependent (100-300 K) conductivity of Berlin green and Prussian blue powders. The method of electronic conduction in vacuum dried Berlin green is identified as hopping of localized electrons and vacuum dried Prussian blue is reaffirmed as an insulator. The assignment of the conduction mechanism is based upon fits to the experimental data, and the different conductivities of the two samples can be understood in terms of both molecular and simple crystalline energy levels of the solids. © 2011 American Physical Society.

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Effect of the doping level on the biological stability of hydrogenated boron doped diamond electrodes

Trouillon Raphaël, O'Hare Danny, Einaga Yasuaki

Physical Chemistry Chemical Physics 13 ( 12 ) 5422 - 5429 2011.03

ISSN 1463-9076

Fouling of electrode surfaces by electrode reaction products or by biological spectator species is known to inactivate electrochemical sensors and thus limit their use in biological conditions. Here we present an investigation on the stability of boron doped diamond (BDD) electrodes with different levels of doping. Three different doping levels were used (0.1, 1 and 5% in the carbon phase). The highly doped (5%) BDD is of particular interest as it is here used for the first time for biological applications. Three different redox reactions were examined based on their electrode reaction characteristics: ruthenium(iii) hexaammine (outer sphere), ferrocyanide (suface dependent), dopamine (adsorption mediated). The effect of albumin at blood concentration was studied. All results were compared with glassy carbon. There were no significant differences for the outer sphere electrochemistry, but all the BDDs showed improved resistance to fouling for the ferrocyanide oxidation. The electrocatalytic activity of BBD towards dopamine oxidation increased with increased boron content. However, this appears to be due to a larger number of defect sites which also increases the vulnerability to fouling by albumin and by electrode reaction products and the 5% BDD had similar properties to glassy carbon in this regard. These results suggest that it is possible to optimise the BDD performance for specific applications and that the large potential window for BDD may be due, at least in part, to its relatively poor electrocatalytic activity. © the Owner Societies.

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Ferromagnetism of Pt nanoparticles induced by surface chemisorption

Sakamoto Yasuhiro, Oba Yojiro, Maki Hideyuki, Suda Masayuki, Einaga Yasuaki, Sato Tetsuya, Mizumaki Masaichiro, Kawamura Naomi, Suzuki Motohiro

Physical Review B - Condensed Matter and Materials Physics 83 ( 10 ) 2011.03

ISSN 1098-0121

The magnetic properties of different-sized Pt nanoparticles coated by alkanethiol molecules with different carbon chain lengths (1-octadecanethiol, 1-dodecanthiol, and 1-octanethiol) were systematically studied by means of magnetic measurement, x-ray magnetic circular dichroism (XMCD), x-ray absorption near-edge structure (XANES), and electron spin resonance (ESR). Furthermore, azobenzene-derivatized thiol coating of Pt nanoparticles was performed to detect the effect on magnetic characteristics of the geometrical transformation between cis and trans states induced by photoisomerization. All samples showed the ferromagnetism inherent in Pt. In all of the prepared particles Curie temperatures above 300 K were observed. The largest magnetization at 5 K was observed for the longest chain length of alkanethiol and the smallest particle size. The coercive force at 5 K increased as the chain length increased and the particle size decreased. The geometrical transformation of coated molecules barely affected the magnetization and coercive force. The increase in coercive force was accompanied by the enhanced contribution of the orbital magnetic moment. The origins of ferromagnetism and magnetic anisotropy in Pt nanoparticles are discussed in terms of the contribution from the coating molecules and downsizing effects. The appearance of ferromagnetism is mainly interpreted based on two mechanisms, i.e., the electronic band magnetism based on the Stoner criterion for ferromagnetism and the orbital ferromagnetism due to electrons captured in the atomiclike orbital on the particle surface. The chain-length and particle-size-dependent magnetic anisotropy is explained in terms of the change in angular momentum depending on the adsorption condition, especially the coverage ratio, of alkanethiol on the particle surface. This is consistent with the existence of orbital ferromagnetism in the Pt nanoparticle. © 2011 American Physical Society.

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Influence of doping level on the electrochemical oxidation of formic acid on boron doped diamond electrodes

Fierro Stéphane, Abe Kyoichi, Comninellis Christos, Einaga Yasuaki

Journal of the Electrochemical Society 158 ( 12 ) 2011

ISSN 0013-4651

The influence of the boron doping level in boron doped diamond electrodes (BDD) on the electro-generation of active intermediates (hydroxyl radicals and hydrogen peroxide) involved in the oxidation of organic compounds has been studied. It is shown that the boron doping level of diamond electrodes has no influence on the amount of hydroxyl radicals produced at the electrode surface in contrast with hydrogen peroxide, whose formation is favored by low boron doping levels. The influence of the boron doping level on the degradation of formic acid is also investigated. It is shown that lowly doped diamond films have a slight advantage; proving that hydrogen peroxide does not participate in the process. Moreover, the experimental results were compared with a theoretical model, which considers that the oxidation reaction is fast and controlled by mass transfer. All BDD electrodes showed a good agreement with the model independently of the boron doping level. However, the accuracy of the model tend to decrease with increasing boron content, which is probably due to the participation of active couples, which are known to be present at the surface of diamond films with high boron doping levels. © 2011 The Electrochemical Society.

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Highly sensitive detection of Cd² using boron doped diamond electrodes

Fierro Stéphane, Watanabe Takeshi, Akai Kazumi, Yamanuki Mikito, Einaga Yasuaki

Journal of the Electrochemical Society 158 ( 11 ) 2011

ISSN 0013-4651

The electrochemical detection of Cd² has been performed by anodic stripping voltammetry on boron doped diamond (BDD) electrodes. A new technique is proposed, which involves adding a known amount of copper to the sample to deposit an amalgam of Cd-Cu on the surface of the BDD electrode. This amalgam is then stripped during voltammetry measurements, allowing the generation of highly accurate calibration curves for Cd detection (r² 0.99) with a lower detection limit of 10 ppb. The conditions that are used for the anodic stripping voltammetry measurements have been optimized to avoid the deposition of cadmium and the appearance of the stripping peak related to copper. Real samples could contain a certain amount of copper, so the influence of small variations of Cu² concentration has been investigated and it was found that such variations have no influence on the accuracy of the calibration curve for Cd detection. The influence of other metals that could be dissolved in the sample has also been studied, and it was shown that lead and selenium have a negative influence on the technique. However, this negative interference can be eliminated by increasing the concentration of copper that is introduced in the sample. Furthermore, other species such as boron or chromium have no influence on the anodic stripping voltammetry measurements, so accurate calibration curves for Cd determination could be constructed in the presence of Pb, Se, B and Cr. © 2011 The Electrochemical Society.

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Surface modification of ferromagnetic L1o FePt nanoparticles using biotin avidin as biomolecular recognition probes

Indrianingsih Anastasia W., Suda Masayuki, Heta Yushi, Suzuki Koji, Einaga Yasuaki

Bulletin of the Chemical Society of Japan 84 ( 8 ) 873 - 877 2011

ISSN 0009-2673

Water-dispersible biotin-modified biofunctional ferromagnetic L1o FePt nanoparticles (NPs) have been synthesized by using a silica nanoreactor strategy. The coercivity field of the NPs was 16 kOe at room temperature, with a particle size of around 5.19 nm. Biotin-coated L1o FePt NPs were biocompatible in an aqueous environment and show site-specific interactions with avidin compounds that could potentially yield a new magnetic material for biological applications, such as for biomolecular recognition.© 2011 The Chemical Society of Japan.

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N,N'-bis(2-hydroxy-3-methoxybenzylidene)-1,3-diaminopropane dimeric 4f and 3d-4f heterodinuclear complexes

Wang Jing Hua, Yan Peng Fei, Li Guang Ming, Zhang Ju Wen, Chen Peng, Suda Masayuki, Einaga Yasuaki

Inorganica Chimica Acta 363 ( 14 ) 3706 - 3713 2010.11

ISSN 0020-1693

Three novel N,N′-bis(2-hydroxy-3-methoxybenzylidene)-1,3- diaminopropane dimeric lanthanide complexes, namely, [{H₂L}Sm(NO ₃)₃]₂·H₂O (1), [{H ₂L}Gd(NO₃)₃]₄·CH ₃OH (2), [{H₂L}Lu(NO₃)₃] ₄·H₂O (3) (H₂L = N,N′-bis(2- hydroxy-3-methoxybenzylidene)-1,3-diaminopropane) and three new N,N′-bis(2-hydroxy-3-methoxybenzylidene)-1,3-diaminopropane 3d-Gd heterodinuclear complexes, namely, [{LCo}(CH₃COO)(CH ₃COOH)Gd(NO₃)₂] (4), [{LNi(MeOH) ₂}Gd(NO₃)₃]·2MeOH (5) and [{(L)Zn(HNO₃)}Gd(NO₃)₃]·NO ₃·H₃O·MeOH (6) have been synthesized and isolated. X-ray crystallographical analysis reveals that complexes 1-3 are isomorphic with unique dimeric topology. Complexes 4-6 are of discrete 3d-4f dinuclear cores. Magnetic properties of complexes 2 and 4-6 are systematically investigated. Complexes 4 and 5 are ferromagnetic, while 2 and 6 are antiferromagnetic. © 2010 Elsevier B.V. All rights reserved.

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Diamond electrodes for electrochemical analysis

Einaga Yasuaki

Journal of Applied Electrochemistry 40 ( 10 ) 1807 - 1816 2010.10

ISSN 0021-891X

We have reported not only the above examples but also several additional examples of sensitive detection by BDD electrodes, such as uric acid [25], NADH [26], acids [27], toxic gases [28], etc. In fact, some of the examples are now in progress for the development of practical electrochemical sensor applications. Furthermore, in order to add other functions and improve the electrochemical properties, BDD electrodes with surfaces chemically modified by functional organic molecules are also actively being developed [29, 30]. Thus, it appears likely that, in the near future, electrochemical sensors using BDD can be applied for environmental analysis and medical analysis. © Springer Science+Business Media B.V. 2010.

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Electrochemical detection of tyrosine derivatives and protein tyrosine kinase activity using boron-doped diamond electrodes

Chiku Masanobu, Horisawa Kenichi, Doi Nobuhide, Yanagawa Hiroshi, Einaga Yasuaki

Biosensors and Bioelectronics 26 ( 1 ) 235 - 240 2010.09

ISSN 0956-5663

In this report, we determined protein tyrosine kinase (PTKs) activity in human epidermoid carcinoma cells (A431) by employing a novel electrochemical method using boron-doped diamond (BDD) electrodes that enables the electrochemical oxidation of tyrosine (Tyr), phosphorylated Tyr (Tyr-P) and sulfated Tyr (Tyr-S) in water-based solutions. Cyclic voltammetry for Tyr, Tyr-P and Tyr-S showed well-defined oxidation peaks at 0.8. V for Tyr, 1.4. V for Tyr-P and 1.7. V for Tyr-S, respectively. Very little work has been reported previously on the detection of Tyr-P and Tyr-S, probably due to their high oxidation potentials. We utilized electrochemical methods for the detection of kinase activity in connection with poly(Glu-Tyr) modified magnetic beads. Linear-sweep voltammograms for the electrochemical detection of PTKs activity were carried out using BDD electrodes consisting of peptide-modified magnetic beads. Without phosphorylation of the peptide-modified magnetic beads using PTKs, we observed clear oxidation peaks for Tyr oxidation and no significant electrochemical responses for Tyr-P oxidation at 1.4. V for the background. On the other hand, with phosphorylation of the beads using PTKs, the peak oxidation current at 1.4. V clearly increased, while the peak oxidation current for Tyr oxidation decreased. This indicates that PTKs activity could be successfully detected by using electrochemical methods employing BDD electrodes. This method was utilized for the in vitro kinase activity detection of human cell lysate, and the electrochemical measurements were compatible with the Enzyme-Linked ImmunoSorbent Assay based method. Our results indicate that the electrochemical method can be applied to real samples such as cell lysate. © 2010 Elsevier B.V.

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Fabrication of Cu-modified boron-doped diamond microband electrodes and their application for selective detection of glucose

Chiku Masanobu, Watanabe Takeshi, Einaga Yasuaki

Diamond and Related Materials 19 ( 7-9 ) 673 - 679 2010.07

ISSN 0925-9635

We describe a simple bench top method for fabricating boron-doped diamond (BDD) microband electrodes and copper-modified BDD microband electrodes. The method described here is inexpensive, robust, renewable, simple, and the BDD microband electrodes and the copper-modified BDD microband electrodes are very easy to fabricate. An advantage of the method is not only its simplicity but also the renewability. That is, even if the surface of the electrode is deactivated after an electrochemical reaction, it can be renewed by simply cutting off the end. As one of the example of application, we report on the selective detection of glucose in solution containing interference species such as Ascorbic acid (AA) and Uric acid (UA) by preparing Cu-modified BDD microband electrodes. Even in solutions containing 2 or 3 times the amount of interfering species compared to the glucose concentration, the Cu-modified BDD microband electrodes showed good selectivity and high durability. © 2010 Elsevier B.V. All rights reserved.

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Giant electric double-layer capacitance of heavily boron-doped diamond electrode

Watanabe Takeshi, Shimizu Tomoko K., Tateyama Yoshitaka, Kim Yousoo, Kawai Maki, Einaga Yasuaki

Diamond and Related Materials 19 ( 7-9 ) 772 - 777 2010.07

ISSN 0925-9635

The physical and electrochemical properties of boron-doped polycrystalline diamond electrodes, prepared with various B/C ratio, i.e., 0.1%, 0.5% (BDD-A), 1% (BDD-B), and 5% (BDD-C), were investigated. Electrochemical measurements of the heavily boron-doped films (BDD-C) showed giant electric double-layer capacitance and activity which is significantly larger than BDD-A and BDD-B as well as glassy carbon electrodes. However, interestingly, actual boron concentration of BDD-C was observed to be almost the same as that of BDD-B by secondary ion mass spectroscopy (SIMS) and glow discharge optical emission spectroscopy (GDOES) analysis. It is suggested that the large capacitance is due to a few sp²-bonded carbon impurities, which was observed only in BDD-C, although the amount of the sp²-bonded nondiamond species are very small. In the present work, the reason for the interesting electrochemical properties of heavily boron-doped diamond electrodes is discussed. Furthermore, dimensional stability of the electrodes was also confirmed by conducting harsh anodic treatment. © 2010 Elsevier B.V. All rights reserved.

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Development of amperometric arsine gas sensor using gold-modified diamond electrodes

Ivandini Tribidasari A., Yamada Daisuke, Watanabe Takeshi, Matsuura Hiroaki, Nakano Nabuo, Fujishima Akira, Einaga Yasuaki

Journal of Electroanalytical Chemistry 645 ( 1 ) 58 - 63 2010.06

ISSN 1572-6657

Amperometric gas sensor of arsine was developed using gold-modified diamond electrodes as the working electrodes. The detection method was conducted in high concentration of H₂SO₄. The reaction was declared based on two oxidation steps, involving oxidation of As^3- to As ⁰ at mild potential in strong acid, followed by electrochemical oxidation of As⁰ to As³⁺ at gold-based electrodes. Linear calibration curve was observed in the concentration range of 5-50 ppb (r ² = 0.985) with detection limit of ∼4.43 ppb (S/N = 3). Current decreasing of measurement was found ∼5.5% for 5 measurements. However, better stability was observed after the 5th measurement, indicated that the sensor could be applied for long time measurement. Investigation to several possible interference gasses, i.e. SO₂, H₂S, NO, NO ₂, CO, O₃ and H₂ indicated no significant interference of the gas to arsine measurements. © 2010 Elsevier B.V. All rights reserved.

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Controlled storage of ferrocene derivatives as redox-active molecules in dendrimers

Ochi Yousuke, Suzuki Mana, Imaoka Takane, Murata Masaki, Nishihara Hiroshi, Einaga Yasuaki, Yamamoto Kimihisa

Journal of the American Chemical Society 132 ( 14 ) 5061 - 5069 2010.04

ISSN 0002-7863

Dendritic polyphenylazomethines (DPA) could encapsulate ferroceniums by complexation of the electron-donating skeleton of the DPA imines. Upon addition of ferroceniums to a series of dendritic polyphenylazomethines (DPAGX, where X is the generation number, X = 1-4), the UV-vis spectra showed changes in a manner similar to that observed for the complexation of metal ions with DPAGX. Stepwise shifts in the isosbestic point were consistently observed with the number of imine groups in the first and second layers of the generation-4 dendrimer (DPAG4). DPAG2 and DPAG3 were also found to trap 6 equiv of ferroceniums. To investigate the complexation, UV-vis spectroscopy, ⁵⁷Fe MoÌssbauer spectroscopy, electrospray ionization-mass spectroscopy (ESI-MS), cyclic voltammetry (CV), and fluorescence spectroscopy were performed. We confirmed that neutral ferrocenes cannot complex with the imine group while ferroceniums can. Utilizing the redox property of ferrocenes, we were able to electrochemically control the encapsulation and release of ferrocenes into the DPA in a manner similar to redox-responsive proteins such as ferritin. In addition to ferrocenes, oligoferrocenes could also be trapped in the DPA. The biferrocene cation(1+) was particularly suitable for electrochemical switching due to its stable mixed valence condition. The terferrocene dication(2+) encapsulated into DPAG4 could be fabricated into a thin film, which exhibited the near-infrared absorption of an intervalence charge-transfer (IV-CT) band, pointing the way toward the use of such systems in material science. © 2010 American Chemical Society.

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Correlations between structure and magnetism of three N,N′-ethylene-bis(3-methoxysalicylideneimine) gadolinium complexes

Gao Ting, Yan Peng Fei, Li Guang Ming, Zhang Ju Wen, Sun Wen Bin, Suda Masayuki, Einaga Yasuaki

Solid State Sciences 12 ( 4 ) 597 - 604 2010.04

ISSN 1293-2558

Three Salen-like gadolinium complexes, namely, mononuclear (4f) complex [{H₂L}Gd(NO₃)₃] (1), heterodinuclear (3d-4f) complex [{LCu}Gd(NO₃)₃]·0.25H₂O (2) and dimeric heterotrinuclear (3d-4f-3d′) complex [{LCu}Gd(H₂O)₃{Fe(CN)₆}]₂·6H₂O (3) [H₂L = N,N′-ethylene-bis(3-methoxysalicylideneimine)] have been synthesized by stepwise reactions. X-ray diffraction analysis reveals that 1 is of a discrete structure in which H₂L coordinates to gadolinium ion through O₂O₂ moiety. Then, addition of Cu(Ac)₂·H₂O to the mononuclear lanthanide complex yields expected heterodinuclear (3d-4f) complexes [{LCu}Gd(NO₃)₃]. 3 features a unique 1D ladder-like topology structure through the intermolecular double links of Cu-N bonds. The measurement of variable-temperature magnetic susceptibility reveals that complex 1 exhibits antiferromagnetic interaction while 2 and 3 exhibit ferromagnetic interaction between spin carriers. The correlations between the structure and magnetism are described and discussed. © 2010.

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Anodic stripping voltammetry of zinc at boron-doped diamond electrodes in ammonia buffer solution

Langeloth Michael, Chiku Masanobu, Einaga Yasuaki

Electrochimica Acta 55 ( 8 ) 2824 - 2828 2010.03

ISSN 0013-4686

This paper describes the deposition of zinc(II) with anodic stripping voltammetry on the boron-doped diamond electrode. We illustrate the dependency of several parameters on the magnitude of the oxidation peak and try to optimize the method. The supporting electrolyte was found to influence the oxidation peak magnitude. Compared with acetic acid, the most frequently used supporting electrolyte, ammonia buffer solution leads to a four times higher signal. We assume that the formation of zinc complexes, primarily tetraaminezinc(II), are responsible for the better response. Further factors studied and assessed include buffer pH, buffer concentration, deposition potential, deposition time and scan rate. With the improved conditions, a final detection limit of 5 ppb was accomplished. © 2010 Elsevier Ltd. All rights reserved.

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Two-dimensional lanthanide-containing coordination Frameworks

Gao Ting, Li Guang Ming, Yan Peng Fei, Zhang Ju Wen, Sun Wen Bin, Suda Masayuki, Einaga Yasuaki

Zeitschrift fur Anorganische und Allgemeine Chemie 636 ( 3-4 ) 624 - 628 2010.03

ISSN 0044-2313

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Reversible optical manipulation of superconductivity

Ikegami Aya, Suda Masayuki, Watanabe Takeshi, Einaga Yasuaki

Angewandte Chemie - International Edition 49 ( 2 ) 372 - 374 2010.01

ISSN 1433-7851

"Chemical Equation Presented" Flicking the switch: Photoirradiation has a dramatic effect on the superconducting properties of a passivated ultrathln Nb film functlonallzed with a photochromic self-assembled azobenzene (AZ) monolayer (see picture). These effects can be attributed to photoisomerization-induced changes in the amount of charge transfer between the substrate and the photochromic monolayer. The changes are accompanied by alternation of the surface dipoles. © 2010 Wiley-VCH Verlag GmbH &. Co. KGaA.

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One-dimensional salen-type heterospin trimetallic (3d-4f-3d′) chain-like coordination polymers

Sun Wen Bin, Yan Peng Fei, Li Guang Ming, Zhang Ju Wen, Gao Ting, Suda Masayuki, Einaga Yasuaki

Inorganic Chemistry Communications 13 ( 1 ) 171 - 174 2010.01

ISSN 1387-7003

Three one-dimensional (1D) heterospin trimetallic chain-like polymers [{LCu(H₂O)}Ln(MeOH)(H₂O)₂{(μ-CN)₂Fe(CN)₄}]·2H₂O (1, Ln = La; 2, Ln = Nd; 3, Ln = Gd) were prepared by substitution of the nitrato ligands in [LCuLn] complexes with [Fe(CN)₆]^3- ions (H₂L = N,N′-bis(3-methoxysalicylidene)propane-1,2-diamine). Single-crystal X-ray diffraction analysis revealed that the methyl on the salen-type ligand impeded the connection between cyanide groups and Cu(II) ions efficiently. Consequently, three novel one-dimensional (1D) trimetallic chain-like polymers were obtained with the linker [Fe(CN)₆]^3- ions interacting only with the lanthanide ions. The magnetic investigation for 3 indicated a ferrimagnetic chain may form. © 2009 Elsevier B.V. All rights reserved.

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Selective detection of As(V) with high sensitivity by as-deposited boron-doped diamond electrodes

Nagaoka Yasutaka, Ivandini Tribidasari A., Yamada Daisuke, Fujita Shinoka, Yamanuki Mikito, Einaga Yasuaki

Chemistry Letters 39 ( 10 ) 1055 - 1057 2010

ISSN 0366-7022

Electrochemical selective detection of not only As(III) but also As(V) has been investigated by anodic stripping voltammetry. Here, instead of using modified working electrodes, simple as-deposited boron-doped diamond (BDD) electrodes were used with the addition of gold ions in the sample solution as a catalyst for the electrochemical reaction. A potential-step technique was performed to minimize the hydrogen evolution effect that occurs at the highly negative potential such as -1.5 V (vs. Ag/AgCl) for the reduction of As(V). The present method realized very high sensitivity with an experimental detection limit of 12ppb and excellent stability for the detection of both As(III) and As(V) as well as mixed solutions of these forms. © 2010 The Chemical Society of Japan.

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Room temperature ferromagnetism at the interface between nonmagnetic semiconductors

Yazaki Yuka, Suda Masayuki, Kameyama Naoto, Einaga Yasuaki

Chemistry Letters 39 ( 6 ) 594 - 595 2010

ISSN 0366-7022

We show experimentally that room-temperature ferromagnetism can be induced in ZnO/ZnS core/shell nanoparticles without any magnetic components. This ferromagnetism could be attributed to p-p coupling interactions between S 3p and O 2p electrons arising from the redistribution of charges between Zn and O or S atoms. Our present findings possibly open up a new way for introducing magnetism in semiconductor-based "spintronics" devices. © 2010 The Chemical Society of Japan.

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An iron(ii) incomplete spin-crossover compound

Yang Feng Lei, Li Bao, Hanajima Taro, Einaga Yasuaki, Huang Rong Bin, Zheng Lan Sun, Tao Jun

Dalton Transactions 39 ( 9 ) 2288 - 2292 2010

ISSN 1477-9226

A one-dimensional iron(ii) spin-crossover compound [Fe(3py-im) ₂(NCS)₂]·7H₂O (1) (3py-im = 2,4,5-tris(4-pyridly)-imidazole) has been solvothermally synthesized and structurally characterized. Compound 1 crystallizes in the monoclinic space group P2/c with a = 11.9078(2), b = 9.9474(1), c = 17.7290(3) and β = 102.361(2)° at 105 K. Studies on the variable-temperature magnetic susceptibilities and Mössbauer spectra suggest that compound 1 undergoes incomplete spin transition behaviour. Pressure effects on the transition behaviour have also been investigated, the thermal-induced spin transition becomes more gradual and the critical temperature shifts towards slightly higher temperature range when external pressure increases. However, the spin transition can not be completed by applying external pressure even as high as 0.79 GPa. © The Royal Society of Chemistry 2010.

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Optical tuning of molecule-induced magnetism at non-magnetic semiconductor nanoparticles

Kameyama Naoto, Suda Masayuki, Einaga Yasuaki

Physica Status Solidi (A) Applications and Materials Science 206 ( 12 ) 2851 - 2856 2009.12

ISSN 1862-6300

We have demonstrated that it is possible to reversibly photo-control the room temperature magnetism in a diluted magnetic semiconductor based on zinc oxide nanoparticles coated with azobenzene-derivatized thiols (Azo-ZnO NPs). These photochromic ligands provide a photo-function and at the same time act as a trigger for the generation of ferromagnetism at ZnO-S interface. UV irradiation increases the saturated magnetization of the Azo-ZnO NPs due to trans- to cis-isomerization in azobenzene-derivatized ligands, and following irradiation with visible light the magnetization is decreased due to inverse isomerization. X-ray photoelectron spectroscopy reveal that the photo-induced magnetization changes are strongly related to photo-induced changes in the chemical state of zinc atom in the ZnO. These photo-magnetic effects can be attributed to photo-induced changes in surface states of the ZnO due to photo isomerization in azobenzene ligands, which is accompanied by alterations in the lowest unoccupied molecular orbital level of the ligand, since magnetic properties of ZnO depend on carrier concentration, which correlated with surface states of the ZnO. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Photoreduction of prussian blue intercalated into titania nanosheet ultrathin films

Yamamoto Takashi, Saso Naoki, Umemura Yasushi, Einaga Yasuaki

Journal of the American Chemical Society 131 ( 37 ) 13196 - 13197 2009.09

ISSN 0002-7863

(Graph Presented) Ultrathin fims composed of titania nanosheets and Prussian Blue were prepared by using the modified Langmuir-Blodgett technique. The ultrathin films could be deposited in a layer-by-layer manner with lamellar structure. Upon band gap excitation of titania nanosheets, the generated electrons were injected into ferromagnetic Prussian Blue, resulting in reduction to paramagnetic Prussian White. It was revealed that the reaction could proceed only in the presence of hole-scavenging interlayer water molecules. © 2009 American Chemical Society.

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Redox-induced modification of magnetism in Ni thin film

Norimasa Hiraoka, Yojiro Oba, Takeshi Watanabe, Hideyuki Maki, Yasuaki Einaga, Tetsuya Sato

e-Journal of Surface Science and Nanotechnology 7 787 - 790 2009.07

Magnetic properties of Ni thin films which were modified through the redox reaction in alkaline solution were investigated by means of magneto-optical Faraday effect. The magnetization process of Ni film on which Ni(II) compounds electrochemically forms was different from that of fresh Ni films. This indicates that the magnetic anisotropy is modified through the redox reaction Ni(0)/Ni(II) which may induce the change in the volume of metallic nickel region and/or the magnetic coupling between the metallic Ni and some compound including Ni(II) formed on the film surface.

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Synthesis, crystal structures, magnetic and luminescent properties of unique 1D p-ferrocenylbenzoate-bridged lanthanide complexes

Yan P. F., Zhang F. M., Li G. M., Zhang J. W., Sun W. B., Suda M., Einaga Y.

Journal of Solid State Chemistry 182 ( 7 ) 1685 - 1690 2009.07

ISSN 0022-4596

Treatments of p-ferrocenylbenzoate [p-NaOOCH₄C₆Fc, Fc=(η⁵-C₅H₅)Fe(η⁵-C ₅H₄)] with Ln(NO₃)₃·nH₂O afford seven p-ferrocenylbenzoate lanthanide complexes {[Ln(OOCH₄C₆Fc)₂(μ₂-OOCH ₄C₆Fc)₂(H₂O)₂] (H₃O)}_n [Ln=Ce (1), Pr (2), Sm (3), Eu (4), Gd (5), Tb (6) and Dy (7)]. X-ray crystallographic analysis reveals that the isomorphous complexes {[Ce(OOCH₄C₆Fc)₂(μ₂-OOCH ₄C₆Fc)₂(H₂O)₂ ](H₃O)}_n (1) and {[Pr(OOCH₄C₆Fc)₂(μ₂-OOCH ₄C₆Fc)₂(H₂O)₂] (H₃O)}_n (2) form a unique 1D double-bridged infinite chain structure bridged by μ₂-OOCH₄C₆Fc groups. Each Ln(III) ion adopts a dodecahedron coordination environment with eight coordinated oxygen atoms from two terminal monodentate coordinated FcC₆H₄COO^- units, two terminal monodentate coordinated H₂O molecules and four μ₂-^-OOCH₄C₆Fc units. The luminescent spectra reveal that only 4 and 6 exhibit characteristic emissions of lanthanide ions, Eu(III) and Tb(III) ions, respectively. The variable-temperature magnetic properties of 5 and 7 suggest that a ferromagnetic coupling between spin carriers may exist in 5. © 2009.

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Size-reduction induced ferromagnetism and photo-magnetic effects in azobenzene-thiol-passivated gold nanoparticles

Suda Masayuki, Kameyama Naoto, Ikegami Aya, Suzuki Motohiro, Kawamura Naomi, Einaga Yasuaki

Polyhedron 28 ( 9-10 ) 1868 - 1874 2009.06

ISSN 0277-5387

We have observed size-reduction induced ferromagnetism and significant photo-magnetic effects in azobezene-thiol-modified gold nanoparticles. When the particle size was reduced to 1.7 nm, ferromagnetism even at room temperature was observed while diamagnetism was dominating with the particle size of 5.0 nm. Furthermore, reducing the particles size to 1.7 nm also gave rise to photo-magnetic properties because the decrease in particle size provided free volume between each of the azobenzene ligands. This photo-magnetic effect could be attributed to photo-induced changes in the values of d-charge losses due to the photoisomerization of azo-ligands, which were accompanied by the inversion of surface dipole values to the opposite sign. © 2008 Elsevier Ltd. All rights reserved.

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Design and fabrication of nickel microdisk-arrayed diamond electrodes for a non-enzymatic glucose sensor based on control of diffusion profiles

Watanabe Takeshi, Einaga Yasuaki

Biosensors and Bioelectronics 24 ( 8 ) 2684 - 2689 2009.04

ISSN 0956-5663

A non-enzymatic glucose sensor, consisting of a regular array of nickel microdisks on a diamond electrode substrate designed to control the diffusion processes of glucose and interfering species such as ascorbic acid and uric acid, was fabricated. Each nickel microdisk acts as a microelectrode for glucose (hemispherical diffusion) due to the inactive diamond surface for glucose oxidation while interfering species are oxidized at the diamond surface (linear diffusion). The difference in diffusion profiles gives a difference in the time dependence of the amperometric response. That is, the glucose concentration gives rise to a constant amperometric response whereas the concentration of mixed interfering species gives rise to a time dependent response, because the hemispherical diffusion profile yields a constant response and the linear diffusion profile yields a transient current following Cottrell's equation. The results show that the fabricated electrodes exhibit a high selectivity for glucose in solutions containing ascorbic and uric acids. © 2009 Elsevier B.V. All rights reserved.

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Enhanced electrochemical response in oxidative differential pulse voltammetry of dopamine in the presence of ascorbic acid at carboxyl-terminated boron-doped diamond electrodes

Kondo Takeshi, Niwano Yu, Tamura Akira, Imai Junichi, Honda Kensuke, Einaga Yasuaki, Tryk Donald A., Fujishima Akira, Kawai Takeshi

Electrochimica Acta 54 ( 8 ) 2312 - 2319 2009.03

ISSN 0013-4686

The differential pulse voltammetric (DPV) peak for dopamine (DA) oxidation was found to be highly amplified by the addition of ascorbic acid (AA) when carboxyl-terminated boron-doped diamond (BDD) electrodes were used as the working electrode. The DP voltammogram for a solution containing DA and AA obtained using a 4-pentenoic acid-modified BDD (4PA-BDD) electrode showed well-separated oxidation peaks for DA and AA at 0.4 and 0.6 V vs. Ag/AgCl, respectively. In addition, as the DA concentration increased at constant AA concentration, a simultaneous increase in the DA peak current density and decrease in the AA peak current density were observed. The slope of the calibration curve for the [DA] range of 1-10 μM in the presence of AA (500 μM) was seven times larger than that obtained in the absence of AA. Such an enhancement was found to be more efficient at 4PA-BDD than at oxidized-BDD, partly due to simple electrostatic effects and partly due to suppression of the polymerization of DA oxidation products by the terminal carboxyl groups. The enhanced detection method using a carboxyl-terminated BDD electrode should be an effective analytical tool, especially for determining low concentrations of DA in the presence of high concentrations of AA. © 2008 Elsevier Ltd. All rights reserved.

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Sequential assembly of phototunable ferromagnetic ultrathin films with perpendicular magnetic anisotropy

Suda Masayuki, Einaga Yasuaki

Angewandte Chemie - International Edition 48 ( 10 ) 1754 - 1757 2009.02

ISSN 1433-7851

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The simple voltammetric analysis of acids using highly boron-doped diamond macroelectrodes and microelectrodes

Mitani Naoko, Einaga Yasuaki

Journal of Electroanalytical Chemistry 626 ( 1-2 ) 156 - 160 2009.02

ISSN 0022-0728

In this paper, the simplest methods developed so far for the analyses of pH and acid concentrations in acid solution are described, using a technique based on highly boron-doped diamond (BDD) electrodes. These simple analyses take advantage of a very attractive electrochemical property of BDD electrodes, i.e., a very wide potential window. It transpires that the value of the current generated by hydrogen evolution during the reduction of an acid when measured by linear sweep voltammetry (LSV) measurements accurately reflects the proton concentration (pH) when using a BDD macroelectrodes (hereafter designated as BDD-M), whereas accurate measurements are impossible when using conventional electrode materials such as glassy carbon, metal etc because of their narrow potential windows. Furthermore, the measurements of weak acid concentrations [HA] were also possible by using both the pH value (obtained by BDD-M) and the limiting current value obtained by using BDD microelectrodes (hereafter designated as BDD-m). © 2008 Elsevier B.V. All rights reserved.

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A spin-crossover cluster of iron(II) exhibiting a mixed-spin structure and synergy between spin transition and magnetic interaction

Wu Da Yu, Sato Osamu, Einaga Yasuaki, Duan Chun Ying

Angewandte Chemie - International Edition 48 ( 8 ) 1475 - 1478 2009.02

ISSN 1433-7851

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Reversible phototuning of the large anisotropic magnetization at the interface between a self-assembled photochromic monolayer and gold

Suda Masayuki, Kameyama Naoto, Lkegami Aya, Einaga Yasuaki

Journal of the American Chemical Society 131 ( 2 ) 865 - 870 2009.01

ISSN 0002-7863

We have observed the emergence of a large anisotropic magnetization and significant photoinduced changes in the magentization that appear at the interface between a gold film and an azobenzene-containing self-assembled monolayer. The magnetization value was extremely high, up to 50 μB per adsorbed molecule. These photomagnetic effects can be attributed to a photoinduced change in the loss of d charge due to photoisomerization of the azobenzene monolayer, which is accompanied by inversion of the surface dipoles. Furthermore, we have also observed reversible changes in the work function of the gold film by alternating UV and visible light, showing that the value of the surface dipole moment is changed as a result of photoisomerization. This allowed us to control the magnetization by alternating the photoillumination between UV and visible light, and we have clarified the mechanism for these photomagnetic effects. A novel strategy such as this, which enables significant reversible phototuning of the magnetic order, has great potential for applications in future magneto-optical devices. © 2009 American Chemical Society.

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Systematic investigation of an array of TCNQ lanthanide complexes

Zhang Juwen, Yan Pengfei, Li Guangming, Hou Guangfeng, Suda Masayuki, Einaga Yasuaki

Dalton Transactions ( 47 ) 10466 - 10473 2009

ISSN 1477-9226

An array of TCNQ (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane) lanthanide complexes, namely, [Ln₂(TCNQ)₄(H₂O) ₁₀(EtOH)₂][2TCNQ]·xH₂O [Ln = La (1, x = 5), Pr (2, x = 3)], [Ln₂(TCNQ)₄(H₂O) ₁₀][2TCNQ]·yH₂O [Ln = Gd (3, y = 6), Dy (4, y = 5)] and [Ln(TCNQ)₂(H₂O)₆][TCNQ]·H ₂O·MeOH [Ln = Er (5), Lu (6)], have been synthesized by salt-elimination reactions. X-ray crystallographic analysis indicates that 1-6 are discrete ion complexes. Cations of 1-4 adopt a dimer structure, while cations of 5 and 6 display a monomer structure. The magnetic study proposes that an antiferromagnetic interaction between TCNQ radicals exists in 1-6. The depopulation of the Stark levels for 2 and 5 leads to a continuous decrease in χ_mT when the samples are cooled from 300 K to 2 K. The desolvated 3, namely, 3a exhibits a unique magnetic conversion from the magnetic disordering to the magnetic ordering at 4 K. 4 shows a ferromagnetic coupling between paramagnetic centers. © 2009 The Royal Society of Chemistry.

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Photochemical modification of a boron-doped diamond electrode surface with vinylferrocene

Kondo Takeshi, Hoshi Hikaru, Honda Kensuke, Einaga Yasuaki, Fujishima Akira, Kawai Takeshi

Journal of Physical Chemistry C 112 ( 31 ) 11887 - 11892 2008.08

ISSN 1932-7447

Boron-doped diamond (BDD) surfaces were photochemically modified with vinylferrocene (VFC), and the modified surfaces were analyzed both qualitatively and quantitatively by electrochemical techniques. VFC-modified BDD (VFC-BDD) was prepared by ultraviolet (254 nm) irradiation of hydrogen-terminated BDD in mesitylene, acetonitrile, or n-alkane solutions of VFC. Cyclic voltammetry (CV) results indicated facile electron transfer between ferrocenyl groups and the BDD substrate. The surface coverage of VFC-modified polycrystalline and single-crystal (100) BDD was also estimated by CV and was found to reach saturation at a value possibly corresponding to monolayer coverage by ferrocenyl groups. The electrochemical stability of VFC-BDD to successive potential cycling in acetonitrile was found to be much higher than that of a self-assembled ferrocenylalkanethiol monolayer on an Au electrode surface. This study is the first to show that appropriate solutions of a terminal alkene can be used in the photochemical modification of diamond, yielding monolayer coverage of the surface. © 2008 American Chemical Society.

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Formation of ε-Fe₂O₃ nanocrystals through segregation in mesoporous silica particles

Mori Kazumi, Oaki Yuya, Suda Masayuki, Einaga Yasuaki, Imai Hiroaki

Chemistry Letters 37 ( 8 ) 814 - 815 2008.08

ISSN 0366-7022

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Conformational change detection in nonmetal proteins by direct electrochemical oxidation using diamond electrodes

Chiku Masanobu, Nakamura Jin, Fujishima Akira, Einaga Yasuaki

Analytical Chemistry 80 ( 15 ) 5783 - 5787 2008.08

ISSN 0003-2700

In this report, we established a new electrochemical method for the detection of conformational changes in large, non-metalloproteins such as bovine serum albumin, using flow injection analysis coupled with hydrogen-terminated, boron-doped diamond electrodes. The oxidation current was used as a signal reporter in the monitoring of urea-induced BSA denaturation. In the denatured state at high urea concentrations, the electrochemical signal increased, and the amperometric responses for the oxidation potential at 1300 mV were consistent with the results of conventional methods of denaturation monitoring using fluorescence spectroscopy. The oxidation involved at least five redox-active species (cysteine, tryptophan, tyrosine, methionine, and disulfide bonds). Furthermore, the method also showed high sensitivity for quantitative analysis of protein. A linear dynamic in the concentration range 50-400 μg/mL (r ² = 0.977) with a lower detection limit of 190 ng/mL was achieved for BSA. Direct electrochemical detection of conformation changes of proteins using BDD electrodes can be performed with advantages in terms of simplicity and sensitivity. © 2008 American Chemical Society.

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Crystal-face-selective adsorption of Au nanoparticles onto polycrystalline diamond surfaces

Kondo Takeshi, Aoshima Shinsuke, Hirata Kousuke, Honda Kensuke, Einaga Yasuaki, Fujishima Akira, Kawai Takeshi

Langmuir 24 ( 14 ) 7545 - 7548 2008.07

ISSN 0743-7463

Crystal-face-selective adsorption of Au nanoparticles (AuNPs) was achieved on polycrystalline boron-doped diamond (BDD) surface via the self-assembly method combined with a UV/ozone treatment. To the best of our knowledge, this is the first report of crystal-face-selective adsorption on an inorganic solid surface. Hydrogen-plasma-treated BDD samples and those followed by UV/ozone treatment for 2 min or longer showed almost no adsorption of AuNP after immersion in the AuNP solution prepared by the citrate reduction method. However, the samples treated by UV/ozone for 10 s showed AuNP adsorption on their (111) facets selectively after the immersion. Moreover, the sample treated with UV/ozone for 40-60 s showed AuNP adsorption on the whole surface. These results indicate that the AuNP adsorption behavior can be controlled by UV/ozone treatment time. This phenomenon was highly reproducible and was applied to a two-step adsorption method, where AuNPs from different batches were adsorbed on the (111) and (100) surface in this order. Our findings may be of great value for the fabrication of advanced nanoparticle-based functional materials via bottom-up approaches with simple macroscale procedures. © 2008 American Chemical Society.

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Sensitive electrochemical detection of oxalate at a positively charged boron-doped diamond surface

Kondo Takeshi, Niwano Yu, Tamura Akira, Ivandini Tribidasari A., Einaga Yasuaki, Tryk Donald A., Fujishima Akira, Kawai Takeshi

Electroanalysis 20 ( 14 ) 1556 - 1564 2008.07

ISSN 1040-0397

Allyltriethylammonium bromide (ATAB) was covalently attached to the surface of hydrogen-terminated boron-doped diamond (BDD) thin films using a photochemical method to fabricate positively charged electrode surfaces. The anodic current for oxalate oxidation both in cyclic voltammetry and in flow-injection analysis with amperometry was found to be up to two times larger at ATAB-modified BDD (ATAB-BDD) than at an unmodified BDD electrode, which may be based on the electrostatic interaction between the oxalate anion and the electrode surface. In addition, the stability of the electrochemical detection of oxalate was improved at the ATAB-BDD electrode compared to the unmodified electrode. © 2008 Wiley-VCH Verlag GmbH&Co. KGaA.

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Photo-control of adhesion properties by detachment of the outermost layer in layer-by-layer assembled multilayer films of Preyssler-type polyozometalate and polyethyleneimine

Nagaoka Yasutaka, Shiratori Seimei, Einaga Yasuaki

Chemistry of Materials 20 ( 12 ) 4004 - 4010 2008.06

ISSN 0897-4756

The ability to generate small-scale structures and assemble functional substances in the fields of micro electronics and optoelectronics continues to support advances in information technology. Here we present a novel type of "layer-by-layer" assembled films, whose surface properties can be controlled by UV irradiation in aqueous solution. We have designed a photochromic multilayer film of Preyssler-type polyoxometalate, (NaP₅W₃₀) and polyethyleneimine (PEI) by using the layer-by-layer method. We found that the outermost PEI layer could be detached by UV irradiation in aqueous solution, and that this process could then cause inversion of the zeta potential. Furthermore, we achieved reversible-control of the surface properties first by UV irradiation, which induced the detachment of the outermost PEI layer, and by subsequent dipping into a PEI solution, which attached a new PEI layer. Finally, we successfully prepared photopatterned films with highly site-selective adsorption abilities by image-wise UV exposure. © 2008 American Chemical Society.

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Evidence of the chemical uniaxial strain effect on electrical conductivity in the spin-crossover conducting molecular system

Takahashi Kazuyuki, Cui Heng Bo, Okano Yoshinori, Kobayashi Hayao, Mori Hatsumi, Tajima Hiroyuki, Einaga Yasuaki, Sato Osamu

Journal of the American Chemical Society 130 ( 21 ) 6688 - 6689 2008.05

ISSN 0002-7863

A novel spin-crossover molecular conductor, [Fe(qnal)₂][Pd(dmit)₂]₅·acetone, was prepared and characterized. The crystal structural analyses of both the low- and high-temperature phases revealed that the supramolecular π-π interactions between the spin-crossover Fe(qnal)₂ cations as well as the cation contraction play an important role in the uniaxial lattice deformation which will modulate the electrical conductivity of the conducting Pd(dmit)₂ layer. Copyright © 2008 American Chemical Society.

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Selective determination of dopamine on a boron-doped diamond electrode modified with gold nanoparticle/polyelectrolyte-coated polystyrene colloids

Wei Min, Sun Li Guo, Xie Zhuo Ying, Zhii Jin Fang, Fujishima Akira, Einaga Yasuaki, Fu De Gang, Wang Xue Mei, Gu Zhong Ze

Advanced Functional Materials 18 ( 9 ) 1414 - 1421 2008.05

ISSN 1616-301X

Negatively charged gold nanoparticles (AuNPs) and a polyelectrolyte (PE) have been assembled alternately on a polystyrene (PS) colloid by a layer-by-layer (LBL) self-assembly technique to form three-dimensional (Au/PAH)₄/(PSS/PAH)₄ multilayer-coated PS spheres (Au/PE/PS multilayer spheres). The Au/PE/PS multilayer spheres have been used to modify a boron-doped diamond (BDD) electrode. Cyclic voltammetry is utilized to investigate the properties of the modified electrode in a 1.0M KCl solution that contains 5.0 × 10^-3 M K₃Fe(CN)₆, and the result shows a dramatically decreased redox activity compared with the bare BDD electrode. The electrochemical behaviors of dopamine (DA) and ascorbic acid (AA) on the bare and modified BDD electrode are studied. The cyclic voltammetric studies indicate that the negatively charged, three-dimensional Au/PE/PS multilayer sphere-modified electrodes show high electrocatalytic activity and promote the oxidation of DA, whereas they inhibit the electrochemical reaction of AA, and can effectively be used to determine DA in the presence of AA with good selectivity. The detection limit of DA is 0.8 × 10^-6M in a linear range from 5 × 10^-6 to 100 × 10^-6M in the presence of 1×10^-3M AA. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

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Anodic stripping voltammetry of inorganic species of As³⁺ and As⁵⁺ at gold-modified boron doped diamond electrodes

Yamada Daisuke, Ivandini Tribidasari A., Komatsu Motoharu, Fujishima Akira, Einaga Yasuaki

Journal of Electroanalytical Chemistry 615 ( 2 ) 145 - 153 2008.04

ISSN 0022-0728

Electrochemical detection of mixture solutions of As³⁺ and As⁵⁺ has been investigated by stripping voltammetry at gold-modified diamond electrodes. The method was performed based on stripping oxidation of As⁰ deposited at the electrode surface. Whereas As³⁺ can be deposited by simple electrochemical reduction of As³⁺ to As⁰ at -0.4 V (vs. Ag/AgCl), much higher potential is required to overcome the activation energy of As⁵⁺ reduction. However, in such a high potential, hydrogen evolution also occurs. Consequently, one more step should be added to release the hydrogen gas adsorbed at the electrode surface during the reduction step. During the deposition of As⁵⁺, As³⁺ species was also simultaneously deposited. Therefore, to differentiate As³⁺ and As⁵⁺ quantification in a mixture solution, both stripping voltammetry methods should be performed and calculated mathematically. Comparison of stripping voltammograms of both methods for As³⁺ solution in the absence of As⁵⁺ demonstrated similar peak shapes and current intensities, confirming that error calculation of As⁵⁺ concentration in the mixture solution with As³⁺ can be avoided. Good linear responses were observed for each standard solution of As³⁺ and As⁵⁺. Linear calibration curve could also be achieved for a series concentrations of 100-1000 ppb As⁵⁺ in a mixture solution with 100 ppb As³⁺ (r² = 0.99) and for a series concentrations of 5-30 ppb As³⁺ in a mixture solution with 100 ppb As⁵⁺. Detection limits of 5 and 100 ppb can be achieved for As³⁺ and As⁵⁺ in a mixture solution, respectively. The reproducibility was shown for stripping voltammetry of As³⁺ and As⁵⁺ with an RSD (n = 8) of 7.5% and 8.4%, respectively. Good stability of gold-modified diamond electrodes before and after arsenic detection was also evaluated by SEM image. Application of the method for real sample analysis was performed for arsenic detection in Yokohama tap water. © 2008 Elsevier B.V. All rights reserved.

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Normal photochromism of spiropyran in montmorillonite interlayer

Saso Naoki, Yamamoto Takashi, Umemura Yasushi, Einaga Yasuaki

Colloids and Surfaces A: Physicochemical and Engineering Aspects 317 ( 1-3 ) 309 - 315 2008.03

ISSN 0927-7757

Spiropyran-montmorillonite hybrid materials have been fabricated by the Langmuir-Blodgett (LB) and an intercalation method. The LB method using clay minerals could be applied to fabricate hybrid ultrathin films consisting of a non-amphiphilic spiropyran. It is confirmed that hybrid LB films possess the layered structure and exhibit "normal photochromism" without any changes in the layered structure. In case of the intercalation method, hybrid compounds also possess the layered structure. Interestingly, intercalation hybrid compounds exhibit "reverse photochromism". It is suggested that a different process in formation of the layered structure influences the observed photochromism. © 2007 Elsevier B.V. All rights reserved.

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Development of amperometric immunosensor using boron-doped diamond with poly(o-aminobenzoic acid)

Preechaworapun Anchana, Ivandini Tribidasari A., Suzuki Akane, Fujishima Akira, Chailapakul Orawon, Einaga Yasuaki

Analytical Chemistry 80 ( 6 ) 2077 - 2083 2008.03

ISSN 0003-2700

An alternative method of a protein immunosensor has been developed at boron-doped diamond (BDD) electrode material. In order to construct the base of the immunosensor, o-aminobenzoic acid (o-ABA) was electropolymerized at an electrode by cyclic voltammetry. The poly-o-ABA-modified BDD was characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The XPS result found that carboxyl groups were formed at the electrode surface. The carboxyl groups were then used to covalently attach protein probes. The amperometric sensing of mouse IgG (MIgG) was selected as the model at the pory-o-ABA-modified BDD to compare to the pory-o-ABA-modified glassy carbon (GC) at the same condition. An antimouse IgG from goat (GaMIgG) was covalently immobilized at a pory-o-ABA-modified BDD electrode which used a sandwich-type alkaline phosphatase (ALP) catalyzing amperometric immunoassay with 2-phospho-L-ascorbic acid (AAP) as substrate. The ALP enzyme conjugated at the immunosensor can generate AAP to the electroactive species of ascorbic acid (AA), which can be determined by amperometric detection. The signal was found to be proportional with the quantity of MIgG. The limits of detection (LODs) of 0.30 (3 SD) and 3.50 ng mL^-1 (3 SD) for MIgG at BDD and GC electrodes were obtained. It also was found that the dynamic range of 3 orders of magnitude (1-1000 ng mL^-1) was obtained at BDD, whereas at GC, the dynamic range was more narrow (10-500 ng mL^-1). The method was applied to a real mouse serum sample that contains MIgG. © 2008 American Chemical Society.

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Direct electrochemical oxidation of proteins at conductive diamond electrodes

Chiku Masanobu, Ivandini Tribidasari A., Kamiya Akihide, Fujishima Akira, Einaga Yasuaki

Journal of Electroanalytical Chemistry 612 ( 2 ) 201 - 207 2008.01

ISSN 0022-0728

Direct oxidation peaks relating to proteins have been clearly observed by exploiting H-terminated boron-doped diamond (BDD) electrodes. Hydrogen generation by reduction treatment was enabled to provide the possibility of using BDD. The pH dependence of bovine serum albumin (BSA) oxidation suggested that the oxidation involved of at least three redox-active amino acid residues (cysteine, tryptophan and tyrosine). Furthermore, the electrochemical detection of not only BSA but also immunosuppressive acidic protein (IAP, a cancer marker) was demonstrated by using cyclic voltammetry and flow injection analysis. A linear dynamic in the concentration range of 5 and 3000 mg/dl (r² = 0.9) with a lower detection limit (LOD) of 5 mg/dl was achieved for BSA. In the case of IAP, the calibration curve was linear over the concentration range from 200 to 800 μg/ml, with an experimental LOD of 100 μg/dl. Excellent reproducibility was also demonstrated, suggested that direct electrochemical detection using BDD electrodes can be performed with advantages in terms of simplicity, sensitivity and stability. © 2007 Elsevier B.V. All rights reserved.

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Tuning of electronic properties of one-dimensional cyano-bridged Cu^II-Ni^II, Cu^II-Pd^II, and Cu^II-Pt^II bimetallic assemblies by stereochemistry of ligands

Akitsu Takashiro, Einaga Yasuaki

Inorganica Chimica Acta 361 ( 1 ) 36 - 42 2008.01

ISSN 0020-1693

Preparations, XPS and electronic spectroscopy, and magnetism of seven new one-dimensional cyano-bridged coordination polymers, chiral [Cu(RR-chxn)₂][Pd(CN)₄] · 2H₂O (1), [Cu(trans-chxn)₂][M(CN)₄] · 2H₂O (2, 4, and 6 for M = Pd, Ni, and Pt), and [Cu(cis-chxn)₂][M(CN)₄] · 2H₂O (3, 5, and 7 for M = Pd, Ni, and Pt) (RR-chxn = cyclohexane-(1R,2R)-diamine, trans-chxn = racemic trans-cyclohexane-(1,2)-diamine, and cis-chxn = racemic cis-cyclohexane-(1,2)-diamine) have been reported in view of tuning of their electronic properties by stereochemistry of chxn ligands and metal-substitution. Comparison of Cu 2p_1/2 and 2p_3/2 peaks of XPS and broad d-d bands around 18 000 cm^-1 of electronic spectra are described systematically for 1-7. Variable-temperature magnetic measurement shows that complexes 1-7 indicate weak antiferromagnetic interactions via cyano-bridges. Because of semi-coordination coupled with pseudo Jahn-Teller elongation and electrostatic interaction for 1, the axial Cu-N coordination bond distances of 2.330(7) and 3.092(8) Å are considerably longer than those of equatorial ones in the range from 2.016(6) to 2.030(6) Å. The former bond distances of 1 are intermediate values among the related Ni (2.324(6) and 3.120(8) Å) and Pt (2.34(1) and 3.09(1) Å) complexes. © 2007 Elsevier B.V. All rights reserved.

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Electrochemical detection of free chlorine at highly boron-doped diamond electrodes

Murata Michio, Ivandini Tribidasari A., Shibata Mamoru, Nomura Satoshi, Fujishima Akira, Einaga Yasuaki

Journal of Electroanalytical Chemistry 612 ( 1 ) 29 - 36 2008.01

ISSN 0022-0728

The quantitative determination of free chlorine based on its oxidation current was studied using cyclic voltammetry (CV) with highly boron-doped diamond (BDD) electrodes. The voltammograms exhibited well-defined anodic peaks and a good linear relationship in the concentration range of 20-100 mg Cl L^-1 using BDD electrodes without any pretreatment. Excellent reproducibility was demonstrated by an RSD of 2.56% (n = 10). The electrochemical behavior of free chlorine at different pH values suggests the optimum condition to be pH 8. Observations with the BDD electrodes terminated with either hydrogen or oxygen suggest that the active species in the anodic reaction was ClO^-. Interference of limited concentration of chloride ion was not observed, whereas exceeded concentration was found to accelerate the electron transfer on chlorine oxidation. Flow injection analysis (FIA) with amperometric detection was used to estimate lower concentrations of free chlorine. A linear relationship (r² = 0.96) was found for the concentration range of 0.1-2 mg L^-1 and the low detection limit (S/N = 3) was estimated to be 8.3 μg L^-1. The results suggest that BDD electrodes are more than adequate for determining the concentration of free chlorine. © 2007 Elsevier B.V. All rights reserved.

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Characterization and electrochemical properties of CF₄ plasma-treated boron-doped diamond surfaces

Kondo Takeshi, Ito Hiroyuki, Kusakabe Kazuhide, Ohkawa Kazuhiro, Honda Kensuke, Einaga Yasuaki, Fujishima Akira, Kawai Takeshi

Diamond and Related Materials 17 ( 1 ) 48 - 54 2008.01

ISSN 0925-9635

The effect of CF₄ plasma etching on diamond surfaces, with respect to treatment time, was investigated using scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. SEM observations and Raman spectra indicated an increase in surface roughening on a scale of 10-20 nm, and an increase in crystal defect density was apparent with treatment time in the range of 10 s to 30 min. In contrast, alteration of the diamond surface terminations from oxygen to fluorine was found to be rather rapid, with saturation of the F/C atomic ratio estimated from XPS analysis after treatment durations of 1 min and more. The redox kinetics of Fe(CN)₆^3-/4- was also found to be significantly modified after 10 s of CF₄ plasma treatment. This behavior shows that C-F terminations predominantly affect the redox kinetics compared to the effect on the surface roughness and crystal defects. The double-layer capacitance (C_dl) of the electrolyte/CF₄ plasma-treated boron-doped diamond interface was found to show a minimum value at 1 min of treatment. These results indicate that a short-duration CF₄ plasma treatment is effective for the fabrication of fluorine-terminated diamond surfaces without undesirable surface damage. © 2007 Elsevier B.V. All rights reserved.

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Comparison of boron-doped diamond and glassy carbon electrodes for determination of procaine hydrochloride

Wei Min, Zhou Yanli, Zhi Jinfang, Fu Degang, Einaga Yasuaki, Fujishima Akira, Wang Xuemei, Gu Zhongze

Electroanalysis 20 ( 2 ) 137 - 143 2008.01

ISSN 1040-0397

The electrochemical oxidation of procaine hydrochloride (PC·HCL, 2-diethylaminoethyl 4-aminobenzoate hydrochloride) was investigated at as-deposited boron-doped diamond (ad-BDD) electrode, anodically oxidized BDD (aoBDD) electrode and glassy carbon (GC) electrode using cyclic voltammetry (CV). Well-defined cyclic voltammograms were obtained for PC·HCL oxidation with high signal-to-background (S/B) ratio, low tendency for adsorption, good reproducibility and long-term stability at ad-BDD electrode, demonstrating its superior electrochemical behavior and significant advantages in contrast to ao-BDD and GC electrode. At 100 μM PC·HCL, the voltammetric S/B ratio was nearly one order of magnitude higher at an ad-BDD electrode than that at a GC electrode. In a separate set of experiments for oxidation of 100 μM PC·HCL, 96%, 92% and 84% of the initial oxidation peak current was retained at the ad-BDD, ao-BDD and GC electrode, respectively, by stirring the solution after the tenth cycle. The current response was linearly proportional to the square root of the scan rate within the range 10-1000 mV s^-1 in 10 μM PC·HCL solutions, indicating that the oxidation process was diffusion-controlled with negligible adsorption at an ad-BDD surface. The good linearity was observed for a concentration range from 5 to 200 μM with a linear equation of y = 0.03517x + 0.65346 (r = 0.999), and the detection limit was 0.5 μM for oxidation of PC·HCL at the adBDD electrode. The ad-BDD electrode could maintain 100% of its original activity after intermittent use for 3 months. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

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Pressure effects and Mössbauer spectroscopic studies on a 3D mixed-valence iron spin-crossover complex with NiAs topology

Bai Yue Ling, Tao Jun, Huang Rong Bin, Zheng Lan Sun, Zheng Shao Liang, Oshida Kazuyoshi, Einaga Yasuaki

Chemical Communications ( 15 ) 1753 - 1755 2008

ISSN 1359-7345

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Reversible phototuning of ferromagnetism at Au-S interfaces at room temperature

Suda Masayuki, Kameyama Naoto, Suzuki Motohiro, Kawamura Naomi, Einaga Yasuaki

Angewandte Chemie - International Edition 47 ( 1 ) 160 - 163 2008

ISSN 1433-7851

Out of nowhere: Significant photoinduced changes in ferromagnetism have been observed at the interfaces between gold nanoparticles (Au NPs) and azobenzene-derivatized thiols. These photomagnetic effects could be attributed to photoinduced changes in d-charge losses resulting from the photoisomerization of the azo ligands (see picture), which are accompanied by the inversion of surface dipoles to the opposite sign. (Figure Presented) © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

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Fabrication, characterization, and application of boron-doped diamond microelectrodes for in vivo dopamine detection

Suzuki Akane, Ivandini Tribidasari A., Yoshimi Kenji, Fujishima Akira, Oyama Genko, Nakazato Taizo, Hattori Nobutaka, Kitazawa Shigeru, Einaga Yasuaki

Analytical Chemistry 79 ( 22 ) 8608 - 8615 2007.11

ISSN 0003-2700

Highly boron-doped diamond (BDD) was deposited on chemically etched micrometer-sized tungsten wires using microwave plasma assisted chemical vapor deposition (MPCVD), and these were used to fabricate BDD microelectrodes. BDD microelectrodes with very small diameter (about 5 μm) and 250 μm in length could be made successfully. In addition to the unique properties of BDD electrodes, such as a very low background current, high stability, and selective oxidation of dopamine (DA) in the presence of ascorbic acid (AA), other superior properties of the microelectrodes, including a constant current response, an increase in the mass transport, and the ability for use in high resistance media were also shown. An application study was conducted for in vivo detection of DA in mouse brain, where the BDD microelectrode was inserted into the corpus striatum of the mouse brain. A clear signal current response following medial forebrain bundle (MFB) stimulation could be obtained with high sensitivity. Excellent stability was achieved, indicating that the BDD microelectrodes are very promising for future in vivo electroanalysis. © 2007 American Chemical Society.

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Fabrication of covalent SAM/Au nanoparticle/boron-doped diamond configurations with a sequential self-assembly method

Kondo Takeshi, Aoshima Shinsuke, Honda Kensuke, Einaga Yasuaki, Fujishima Akira, Kawai Takeshi

Journal of Physical Chemistry C 111 ( 34 ) 12650 - 12657 2007.08

ISSN 1932-7447

An attempt was made to make use of chemical modification of the diamond surface to control the adsorption of Au nanoparticles (AuNPs) on this surface via self-assembly. AuNPs prepared with a citrate reduction method (c-AuNP) and mercaptoacetic acid (MAA)-modified AuNPs (MAA-AuNP) were not adsorbed onto hydrogen-terminated and oxygen-terminated boron-doped diamond (BDD) surfaces. On the other hand, c-AuNP and MAA-AuNP were found to be adsorbed in a homogeneous, well-dispersed fashion on NH₂-terminated and SH-terminated BDDs prepared with the silane coupling method. It was also found that the adsorption of c-AuNP on SH-BDD was more stable than that on NH₂-BDD versus immersion in various thiol aqueous solutions used to form self-assembled monolayers (SAMs) on the Au surface, without desorption of the AuNP from the BDD surface. Immersion of the c-AuNP/SH-BDD sample in a ferrocenylalkanethiol/ ethanol solution was found, by cyclic voltammetry, to result in chemisorption of the thiol to the Au surface. Facile electronic communication through the ferrocenyl moiety to the BDD substrate suggests that SAM/AuNP/BDD configurations based on SH-BDD fabricated by a self-assembly method can be applied to possible molecular electronic and electrochemical devices. © 2007 American Chemical Society.

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Structure of cyano-bridged Eu(III)-Co(III) bimetallic assembly and its application to photophysical verification of photomagnetic phenomenon

Akitsu T., Einaga Y.

Chemical Papers 61 ( 3 ) 194 - 198 2007.06

ISSN 0366-6352

New crystal structure of Eu(DMF)₄(H₂O) ₃Co(CN)₆•H₂O (DMF = N,N′- dimethylformamide) (Eu-Co) has been determined to be monoclinic, P2(1)/n, a = 19.796(12) Å, b = 8.862(11) Å, c = 17.525(10) Å, β = 96.26(5)°, V = 3056(5) Å³, Z = 4. The Eu(III) ion adopts an antiprismatic eight-coordination and forms a cyano bridge with r(Eu-N) = 2.496(7) Å and Θ(Eu-N-C) = 165.7(7)° to the Co(III) ion. The complex exhibits some common features with the Eu-Fe complex. Diffuse reflectance electronic spectra and magnetic susceptibility of Eu-Cr, Eu-Mn, Eu-Fe, and Eu-Co complexes were compared. By substituting the metal ions, both electronic and structural features affected the charge transfer bands and superexchange interactions concerning cyanide ligands. In addition, only Eu-Co exhibited ⁵ D ₀ → ⁷ F ₂ and ⁵ D ₀ → ⁷ F ₁ luminescence bands at 16300 cm^-1 and 16900 cm^-1, respectively at 298 K (λ_ex = 360 nm (27000 cm^-1)), because quenching by cyano-bridged ions did not prevent Eu(III) ion from exhibiting emission. Thus, only Eu-Co may be suitable for verification of an assumption of mechanism concerning drastic photoinduced magnetic changes for Nd-Fe. Merely small decrease of magnetization was observed for Eu-Co after UV light irradiation at 2.0 K. This result was attributed to slight structural changes around cyano bridges without transitions of spin states. © Institute of Chemistry, Slovak Academy of Sciences 2007.

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Photomagnetic hybrid ultrathin films

Yamamoto Takashi, Einaga Yasuaki

Journal of Solid State Electrochemistry 11 ( 6 ) 781 - 790 2007.06

ISSN 1432-8488

Two novel types of photomagnetic hybrid ultrathin film (film A and B) of metal cyanides have been fabricated by means of the modified Langmuir-Blodgett method using a smectite clay mineral. Film A is composed of an amphiphilic azobenzene cation, a montmorillonite, and Prussian Blue in which photocontrol in the magnetization was realized by the photoisomerization of azobenzene chromophore. The observed photomagnetic efficiency was large (ca. 11%) due to the well-organized structure of the ultrathin film. Film B is composed of a quaternary ammonium salt, a montmorillonite, and Co-Fe Prussian Blue in which the photoinduced magnetization caused by the electron transfer exhibited an anisotropic response with regards to the direction of the applied magnetic field. This phenomenon is ascribed to the unique structure of Co-Fe Prussian Blue formed onto the clay layer. © Springer-Verlag 2007.

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Photochromism induced magnetization changes in Prussian Blue ultrathin films fabricated into the Langmuir-Blodgett films composed of an amphiphilic azobenzene and a deoxyribonucleic acid

Yamamoto Takashi, Umemura Yasushi, Nakagawa Masaru, Iyoda Tomokazu, Einaga Yasuaki

Thin Solid Films 515 ( 13 ) 5476 - 5483 2007.05

ISSN 0040-6090

A photomagnetic ultrathin film consisting of an azobenzene, a deoxyribonucleic acid, and Prussian Blue has been fabricated by the Langmuir-Blodgett method. Prussian Blue layers in the films were a two-dimensional structure with the height of 50 Å and the average coherence length of 210 Å. Reversible photoisomerization of the azobenzenes was observed even in the films. The films exhibit the long-range ferromagnetic order below 4.2 K and moreover, upon photoillumination at 2 K, reversible changes in the magnetization were realized with the value of ca. 1.0%. This photoswitching in the magnetization is due to changes in the electrostatic field induced by photoisomerization. © 2007 Elsevier B.V. All rights reserved.

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Photo-control of the electronic states of Iron coordinated to photo-responsive polyaniline

Oshida Kazuyoshi, Einaga Yasuaki

Thin Solid Films 515 ( 13 ) 5484 - 5489 2007.05

ISSN 0040-6090

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Reversible photoswitching of ferromagnetic FePt nanoparticles at room temperature

Suda Masayuki, Nakagawa Masaru, Iyoda Tomokazu, Einaga Yasuaki

Journal of the American Chemical Society 129 ( 17 ) 5538 - 5543 2007.05

ISSN 0002-7863

There has been a great interest in developing photoswitchable magnetic materials because of their possible applications for future high-density information storage media. In fact, however, the examples reported so far did not show ferromagnetic behavior at room temperature. From the viewpoint of their practical application to magnetic recording systems, the ability to fix their magnetic moments such that they still exhibit room-temperature ferromagnetism is an absolute requirement. Here, we have designed reversible photoswitchable ferromagnetic FePt nanoparticles whose surfaces were coated with azobenzene-derivatized ligands. On the surfaces of core particles, reversible photoisomerization of azobenzene in the solid state was realized by using spacer ligands that provide sufficient free volume. These photoisomerizations brought about changes in the electrostatic field around the core-FePt nanoparticles. As a result, we have succeeded in controlling the magnetic properties of these ferromagnetic composite nanoparticles by alternating the photoillumination in the solid state at room temperature. © 2007 American Chemical Society.

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Plasma etching treatment for surface modification of boron-doped diamond electrodes

Kondo Takeshi, Ito Hiroyuki, Kusakabe Kazuhide, Ohkawa Kazuhiro, Einaga Yasuaki, Fujishima Akira, Kawai Takeshi

Electrochimica Acta 52 ( 11 ) 3841 - 3848 2007.03

ISSN 0013-4686

Boron-doped diamond (BDD) thin film surfaces were modified by brief plasma treatment using various source gases such as Cl₂, CF₄, Ar and CH₄, and the electrochemical properties of the surfaces were subsequently investigated. From X-ray photoelectron spectroscopy analysis, Cl and F atoms were detected on the BDD surfaces after 3 min of Cl₂ and CF₄ plasma treatments, respectively. From the results of cyclic voltammetry and electrochemical AC impedance measurements, the electron-transfer rate for Fe(CN)₆^3-/4- and Fe^2+/3+ at the BDD electrodes was found to decrease after Cl₂ and CF₄ plasma treatments. However, the electron-transfer rate for Ru(NH₃)₆^2+/3+ showed almost no change after these treatments. This may have been related to the specific interactions of surface halogen (C-Cl and C-F) moieties with the redox species because no electrical passivation was observed after the treatments. In addition, Raman spectroscopy showed that CH₄ plasma treatment of diamond surfaces formed an insulating diamond-like carbon thin layer on the surfaces. Thus, by an appropriate choice of plasma source, short-duration plasma treatments can be an effective way to functionalize diamond surfaces in various ways while maintaining a wide potential window and a low background current. © 2006 Elsevier Ltd. All rights reserved.

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Simultaneous detection of purine and pyrimidine at highly boron-doped diamond electrodes by using liquid chromatography

Ivandini Tribidasari A., Honda Kensuke, Rao Tata N., Fujishima Akira, Einaga Yasuaki

Talanta 71 ( 2 ) 648 - 655 2007.02

ISSN 0039-9140

Highly boron-doped diamond (BDD) electrode, have been examined for simultaneous detection of purine and pyrimidine bases in mild acidic media by using HPLC with amperometric detection. Cyclic voltammetry at as-deposited (AD) and anodically oxidized (AO) BDD were used to study the electrochemistry and to optimize the condition for HPLC applications. At AO BDD electrode, due to its higher overpotential of oxygen evolution reaction, well-defined anodic peaks were observed for the oxidation of purine and pyrimidine bases in acid medium, whereas at AD BDD the oxidation peak of thymine was overlapped with the anodic current of oxygen evolution. The chromatograms of adenine, guanine, cytosine, thymine and 5-methylcytosine mixture were well resolved by using a silica-based column and a solution of 5% acetonitrile in 100 mM ammonium acetate buffer (pH 4.25) as the mobile phase. The detection was carried out at AO BDD electrode at an applied potential of 1.6 V versus Ag/AgCl. Linear calibration curves were obtained within the concentration range from 0.1 to 10 μM with the limits of detection (S/N = 3) ranging from 26.3 to 162.1 nM, resulting in an order of magnitude higher sensitivities than those at conventional electrodes. HPLC analysis with diamond amperometric detector was successfully applied for determination of 5-methylcytosine in real DNA samples with high reproducibility. No deactivation of the electrode was found during cyclic voltammetric and HPLC measurements, indicating the high stability for analysis of biological samples. © 2006 Elsevier B.V. All rights reserved.

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Structures, magnetic properties, and XPS of one-dimensional cyanide-bridged Cu^II-Ni^II/Pt^II bimetallic assembly complexes

Akitsu Takashiro, Einaga Yasuaki

Inorganica Chimica Acta 360 ( 2 ) 497 - 505 2007.02

ISSN 0020-1693

Synthesis, crystal structures, and spectroscopic and magnetic properties of new one-dimensional cyano-bridged bimetallic complexes, [Cu^II(N-Eten)₂][M^II(CN)₄] (N-Eten = N-ethylethylenediamine; M^II = Ni^II (1) and Pt^II (2)), have been reported. Both complexes consist of one-dimensional alternate chains of Cu^II and M^II moieties. The Pt-C bond distances of 1.997(3) and 2.001(3) Å for 2 are considerably longer than the Ni-C bond lengths of 1.866(3) and 1.872(3) Å for 1. Because of pseudo Jahn-Teller distortion, the axial Cu-N bond distances of 2.554(2) and 2.550(3) Å for 1 and 2 are longer than those of equatorial ones of 2.008(2) and 2.056(2) Å for 1 and 2.010(2) and 2.054(2) Å for 2. In contrast to M^II-C bond distances, the Cu-N ones of 1 are similar to those of 2 regardless of element-substitution. These complexes indicate weak antiferromagnetic interactions with Weiss constants = - 4.68 and -3.95 K for 1 and 2, respectively. The emission spectrum of 2 (λ_ex = 360 nm) exhibits a broad band with peaks at 22 800 and 24 000 cm^-1 at 298 K. The Cu 2p_1/2 and 2p_3/2 peaks of XPS spectra are compared systematically to various copper(II) complexes showing different bridging features or distorted coordination geometries as models for excited structures induced by external physical conditions. The spectroscopic properties are discussed from the viewpoint of magneto-optical properties. © 2006 Elsevier B.V. All rights reserved.

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Direct electrochemical detection of sodium azide in physiological saline buffers using highly boron-doped diamond electrodes

Suzuki Akane, Ivandini Tribidasari A., Kamiya Akihide, Nomura Satoshi, Yamanuki Mikito, Matsumoto Koichi, Fujishima Akira, Einaga Yasuaki

Sensors and Actuators, B: Chemical 120 ( 2 ) 500 - 507 2007.01

ISSN 0925-4005

Direct detection of sodium azide was examined by using highly boron-doped diamond (BDD) electrodes in some physiological saline buffer solutions. Three important saline buffers, ADA buffer (N-(2-acetamido) iminodiacetic acid), sodium EDTA and imidazole, were investigated. Hydrogen-terminated BDD was fixed for the investigation since it showed much better sensitivity for azide oxidation in comparison with the oxygen-terminated one. Wide range of buffer concentration was examined. A well-separated peak of sodium azide was observed in its mixture with the buffers, resulting in selective sodium azide detection. The current responses were exactly total addition of sodium azide and buffer current responses. The present method was evidenced to be available for direct detection of sodium azide in two samples of commercial diluents for cell counting. A standard addition method was applied. Sodium azide concentrations of 502 and 1355 μg mL^-1 were detected in both samples with the R.S.D.s of 0.07 and 2.37%, respectively. Validation was achieved by the comparison with the sample concentrations given by the manufacturer. Simple, selective, good sensitivity and excellent reproducible detection make the diamond electrodes very attractive for numerous electroanalytical applications. © 2006 Elsevier B.V. All rights reserved.

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Heterometal assembly in dendritic polyphenylazomethines

Takanashi Kensaku, Fujii Atsunobu, Nakajima Reina, Chiba Hiroshi, Higuchi Masayoshi, Einaga Yasuaki, Yamamoto Kimihisa

Bulletin of the Chemical Society of Japan 80 ( 8 ) 1563 - 1572 2007

ISSN 0009-2673

Fine-controlled metal-organic hybridization is strongly desired for advanced nano-materials. Dendrimers are highly branched organic macromolecules with successive layers or "generations" of branch units surrounding a central core. Metal-organic hybrid versions have also been produced by trapping metal ions or metal clusters within the voids of dendrimers. Here, we report a technique to form a dendritic organic structure, which includes various metals, with fine control over the number and location of the metal salts through a radial stepwise complexation. FeCl₃, GaCl₃,VCl ₃, and SnCl₂ were decorated on a phenylazomethine dendrimer with 4th generations at the first, second, third, and forth layers, respectively. These stepwise complexation and heterometal assembling were also supported by TEM observation, ⁵⁷Fe Mössbauer spectroscopy, XPS measurement, and NMR spectroscopy. © 2007 The Chemical Society of Japan.

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Pulsed amperometry for anti-fouling of boron-doped diamond in electroanalysis of β-agonists

Karuwan Chanpen, Mantim Thitirat, Chaisuwan Patcharin, Wilairat Prapin, Grudpan Kate, Jittangprasert Piyada, Einaga Yasuaki, Chailapakul Orawon, Suntornsuk Leena, Anurukvorakun Oraphan, Nacapricha Duangjai

Sensors 6 ( 12 ) 1837 - 1850 2006.12

ISSN 1424-3210

This work presents the construction and application of boron-doped diamond (BDD) thin film electrode as sensor for the determination of three β-agonists, viz. salbutamol, terbutaline and clenbuterol. Although well-known as a chemically inert material, BDD film however shows fouling in detection of these compounds using fixed-potential mode amperometry. A suitable waveform for pulsed amperometric detection (PAD) was developed and used to determine the agonist compounds. It was seen that the developed PAD significantly refreshed the BDD surface for long-term detection in flow injection analysis. Linear working ranges were 0.5-100 μM, 1.0-100 μM and 0.5-50 μM for salbutamol, terbutaline and clenbuterol, respectively. The developed PAD-BDD system was applied to successfully determine salbutamol and terbutaline in commercial pharmaceutical products. The methods were validated with a capillary electrophoresis method. © 2006 by MDPI.

Extremely long axial Cu-N bonds in chiral one-dimensional zigzag cyanide-bridged Cu^II-Ni^II and Cu^II-Pt ^II bimetallic assemblies

Akitsu Takashiro, Einaga Yasuaki

Inorganic Chemistry 45 ( 24 ) 9826 - 9833 2006.11

ISSN 0020-1669

Preparations, crystal structures, and spectral and magnetic properties of two new chiral one-dimensional cyano-bridged coordination polymers, [Cu ^IIL₂][M^II(CN)₄]·2H ₂O (M^II = Ni^II (1) and Pt^II (2), L = trans-cyclohexane-(1 R,2R)-diamine) have been presented. Complex 1 crystallizes in the monoclinic P2₁ space group with a = 9.864(4) Å, b = 15.393(8) Å, c = 7.995(4) Å, β = 110.32(3)°, V = 1138.4(10) Å³, and Z = 2, while 2 crystallizes in the monoclinic P2 ₁ space group with a = 9.899(3) Å, b = 15.541(4) Å, c = 8.102(2) Å, β = 111.02(2)°, V = 1163.6(5) Å³, and Z = 2. The unique zigzag cyano-bridged chains along the crystallographic b axis consist of alternate chiral [CuL₂]²⁺ cations and square-planar [M(CN)₄]^2- anions. One side of the axial Cu-N(≡C) bond distances are 2.324(6) and 2.34(1) Å with Cu-N≡C angles of 137.8(6)° and 138.2(9)° for 1 and 2, respectively. On the other hand, the opposite side of the axial Cu-N(≡C) bond distances are 3.120(8) and 3.09(1) Å with significantly large bent Cu-N≡C angles of 97.9(5)° and 96.8(7)° for 1 and 2, respectively. The novel axial bonding features of extremely long semi-coordination Cu-N bonds are attributed to coexistence of pseudo-Jahn-Teller elongation and electrostatic interaction in the unique zigzag cyano-bridged chains. The characteristic bonding features with overlap between small 3d (Ni^II) or large 5d (Pt^II) and 3d (Cu^II) orbitals results in larger shifts in XPS peaks of not only Cu2p_1/2 and Cu2p_3/2 but also Ni2p_1/2 and Ni2p_3/2 for 1 than those of 2, which is also consistent with weak antiferromagnetic interactions with Weiss constants of -5.31 and -5.94 K for 1 and 2, respectively. The d-d, π-π*, and CT bands in the electronic, CD, and MCD spectra for 1 and 2 in the solid state at room temperature are discussed from the viewpoint of magneto-optical properties. © 2006 American Chemical Society.

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Selective detection method derived from a controlled diffusion process at metal-modified diamond electrodes

Watanabe Takeshi, Ivandini Tribidasari A., Makide Yoshihiro, Fujishima Akira, Einaga Yasuaki

Analytical Chemistry 78 ( 22 ) 7857 - 7860 2006.11

ISSN 0003-2700

A novel, selective methodology is derived based on the difference between the diffusion processes at microelectrodes (i.e., hemispherical diffusion) and the macroelectrode (i.e., linear diffusion) in a metal-implanted boron-doped diamond electrode (metal-BDDs). As an example, the selective detection of glucose in a solution containing interference species such as ascorbic acid and uric acid is demonstrated. The electrochemical properties of BDD, which are low background current, extremely high stability, and (especially) inactivity toward glucose, play an important role in realizing these differences in the diffusion characteristics. The present methodology can be applied not only to selective glucose detection by the metal-BDD system but also to other selective detection systems. © 2006 American Chemical Society.

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Novel photo-induced aggregation behavior of a supramolecular system containing iron(III) magnetic ionic liquid and azobenzene

Akitsu Takashiro, Einaga Yasuaki

Inorganic Chemistry Communications 9 ( 11 ) 1108 - 1110 2006.11

ISSN 1387-7003

New photo-controllable supramolecular system containing magnetic ionic liquid (iron(III) chloride with 1-butyl-3-methylimidazolium chloride) and azobenzene has been prepared. Reversible structural changes due to cis-trans photoisomerization of azobenzene could be observed by means of resonance Raman and electronic spectroscopy. Field dependence of magnetic moment at 298 K exhibited paramagnetic behavior similar to pure iron(III) magnetic ionic liquid. Alternate irradiation of UV and visible light at 298 K resulted in a monotonous increase of magnetic moment. In analogy with previous study, the novel behavior can be explained as irreversible aggregation of paramagnetic iron(III) complexes forming a short-range order in the supramolecular system. © 2006 Elsevier B.V. All rights reserved.

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Photo-switching magnetic materials

Einaga Yasuaki

Journal of Photochemistry and Photobiology C: Photochemistry Reviews 7 ( 2-3 ) 69 - 88 2006.10

ISSN 1389-5567

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A chiral photochromic Schiff base

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 62 ( 10 ) 2006.10

ISSN 1600-5368

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Electrochemical detection of arsenic(III) using indium-implanted boron-doped diamond electrodes

Ivandini Tribidasari A., Sato Rika, Makide Yoshihiro, Fujishima Akira, Einaga Yasuaki

Analytical Chemistry 78 ( 18 ) 6291 - 6298 2006.09

ISSN 0003-2700

Indium-modified, boron-doped diamond electrodes fabricated by an ion implantation method have been developed for electrochemical detection of arsenite (As(III)). Ir⁺ ions were implanted with an energy of 800 keV and a dose of 10¹⁵ ion cm^-2. An annealing treatment at 850 °C for 45 min in H₂ plasma (80 Torr) was required to rearrange metastable diamond produced by an implantation process. Characterization was investigated by SEM, AFM, Raman, and X-ray photoelectron spectroscopy. Cyclic voltammetry and flow injection analysis with amperometric detection were used to study the electrochemical reaction. The electrodes exhibited high catalytic activity toward As(III) oxidation with the detection limit (S/N = 3), sensitivity, and linearity of 20 nM (1.5 ppb), 93 nA μM ^-1 cm^-2, and 0.999, respectively. The precision for 10 replicate determinations of 50 μM As(III) was 4.56% relative standard deviation. The advantageous properties of the electrodes were its inherent stability with a very low background current. The electrode was applicable for analysis of spiked arsenic in tap water containing a significant amount of various ion elements. The results indicate that the metal-implanted method could be promising for controlling the electrochemical properties of diamond electrodes. © 2006 American Chemical Society.

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Structures and XPS studies of several 3d-4f cyano-bridged Ln^III-Fe^III/Co^III heterometallic complexes

Akitsu Takashiro, Einaga Yasuaki

Polyhedron 25 ( 13 ) 2655 - 2662 2006.09

ISSN 0277-5387

Characterization and crystal structure determination of 3d-4f cyano-bridged bimetallic assemblies, Ln(DMF)₄(H₂O)₃Co(CN)₆ · H₂O (DMF = N,N′-dimethylformamide, Ln = Tb, Dy, Ho and Er) have been newly carried out. We have observed their isostructural features and gradual decreasing cell constants and corresponding changes of local bond distances and angles around the cyano-bridges in accord with the ionic radii changes due to lanthanoid contraction. In order to elucidate the reasons that only Nd-Fe and Nd-Co complexes can exhibit photo-induced magnetic functions, we have also investigated the electronic properties for several analogous 3d-4f complexes, Ln(DMF)₄(H₂O)₃M(CN)₆ · H₂O (Ln = Ce, Nd, Sm, Gd, Tb, Dy, Ho and Er; M = Co and Fe), by means of X-ray photoelectron spectroscopy (XPS). We found that the characteristic bent features of Nd-N-C bond angles and the slight shift of binding energies of Ln 4d_3/2 peaks in the 3d-4f systems being closed to mixed-valence states might be the reasons for the novel functions. © 2006 Elsevier Ltd. All rights reserved.

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Photocontrolled magnetization of CdS-modified prussian blue nanoparticles

Taguchi Minori, Yagi Ichizo, Nakagawa Masaru, Iyoda Tomokazu, Einaga Yasuaki

Journal of the American Chemical Society 128 ( 33 ) 10978 - 10982 2006.08

ISSN 0002-7863

The first photocontrollable magnetic nanoparticles containing CdS and Prussian blue (PB) have been created using reverse micelles as nanoreactors. Photoinduced electron transfer from CdS to PB in the reverse micelle changed the magnetic properties of the composite nanoparticles from ferromagnetic to paramagnetic. The magnetization in the ferromagnetic region below 4 K was substantially decreased after UV light illumination and could be restored almost to its original level by thermal treatment at room temperature. This novel strategy of designing composite nanoparticles containing photoconductive semiconductors and magnetic materials to create photoswitchable magnetic materials may open many possibilities in the development of magneto-optical devices. © 2006 American Chemical Society.

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Photomodulation of a chiral nematic liquid crystal by the use of a photoresponsive ruthenium(III) complex

Mitsuoka Tadashi, Sato Hisako, Yoshida Jun, Yamasishi Akihiko, Einaga Yasuaki

Chemistry of Materials 18 ( 15 ) 3442 - 3447 2006.07

ISSN 0897-4756

We have attempted to control the helical pitch of a chiral nematic liquid crystal by the use of a photoresponsive chiral metal complex. For this purpose, a novel Ru(III) complex [Ru(acac)₂(L)] was synthesized, where acac and L denote acetylacetonato and 1,3-bis-{4-[6-(4-phenylazo-phenoxy)-hexyloxy]- phenyl}-propane-1,3 -dionato, respectively. The complex underwent cis-trans photoisomerization in methanol when under UV (λ_max = 360 nm) or visible (λ_max = 450 nm) light illumination, respectively. When the complex was doped into a room-temperature nematic liquid crystal (ZLI-1132), it induced a chiral nematic phase. Under illumination with UV or visible light, the helical pitch of the chiral nematic phase could be changed reversibly by up to 50%. Corresponding to this change, the helical twisting power (HTP) of the complex varied between 34.0 and 22.0 μm^-1, or between -43.9 and -26.6 μm^-1 at 35.0 °C, where the positive and negative signs corresponded to the A- and Δ-enantiomers, respectively. This has been the first attempt at combining the ΔΛ chirality of an octahedral metal complex with the cis-trans isomerization of an azobenzene group in the development of a photoresponsive dopant. © 2006 American Chemical Society.

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Electrical conductivity modulation coupled to a high-spin-low-spin conversion in the molecular system [Fe^III(qsal)₂][Ni(dmit) ₂]₃·CH₃CN·H₂O

Takahashi Kazuyuki, Cui Heng Bo, Okano Yoshinori, Kobayashi Hayao, Einaga Yasuaki, Sato Osamu

Inorganic Chemistry 45 ( 15 ) 5739 - 5741 2006.07

ISSN 0020-1669

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Electrochemical oxidation of oxalic acid at highly boron-doped diamond electrodes

Ivandini Tribidasari A., Rao Tata N., Fujishima Akira, Einaga Yasuaki

Analytical Chemistry 78 ( 10 ) 3467 - 3471 2006.05

ISSN 0003-2700

Electrochemical oxidation of oxalic acid has been investigated at bare, highly boron-doped diamond electrodes. Cyclic voltammetry and flow injection analysis with amperometric detection were used to study the electrochemical reaction. Hydrogen-terminated diamonds exhibited well-defined peaks of oxalic acid oxidation in a wide pH range. A good linear response was observed for a concentration range from 50 nM to 10 μM, with an estimated detection limit of ∼0.5 nM (S/N = 3). In contrast, oxygen-terminated diamonds showed no response for oxalic acid oxidation inside the potential window, indicating that surface termination contributed highly to the control of the oxidation reaction. An investigation with glassy carbon electrodes was conducted to confirm the surface termination effect on oxalic acid oxidation. Although a hydrogen-terminated glassy carbon electrode showed an enhancement of signal-to-background ratio in comparison with untreated glassy carbon, less stability of the current responses was observed than that at hydrogen-terminated diamond. © 2006 American Chemical Society.

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Bis(N-ethylethylenediamine-κ²N,N′)copper(II) -hexacyanocobaltate(III)-water (3/2/4)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 62 ( 4 ) 2006.04

ISSN 1600-5368

The title compound, poly[[tetracyano-octa-μ-cyano-hexakis-(N- ethylethylenediamine)tricopper(II)dicobaltate(III)] tetrahydrate], [Cu(C ₄H₁₂N₂)₂]₃[Co(CN) ₆]₂·4H₂O or {[Cu₃Co ₂-(CN)₁₂(C₄H₁₂N₂) ₆]·4H₂O}_n, was crystallized from an aqueous reaction mixture containing Cu(ClO₄)₂, N-ethylethylenediamine and K₃[Co(CN)₆] in a self-assembling process. The polymeric chains are extended through -Co ^III-CN-Cu^II-linkages involving four or two cyanide ligands of the centrosymmetric [Co(CN)₆]^3- complex ions, forming a two-dimensional ladder structure. The Cu^II atoms, one of which also lies on an inversion centre, have a distorted octahedral coordination geometry, the degree of tetragonal Jahn-Teller distortion being T = 0.785 and 0.810 (T is the ratio of mean inplane Cu - N bond lengths to axial Cu - N bond lengths). This local Jahn-Teller distortion results from the anisotropic features of this two-dimensional cyano-bridged structure. © 2006 International Union of Crystallography All rights reserved.

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The one-dimensional chain structure of [Cu(en)₂Pt(CN) ₄] (en is ethylenediamine)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 62 ( 4 ) 2006.04

ISSN 1600-5368

The title compound, catena-poly[di-μ-cyano-1:2κ²C:N;-1: 2′κ²C:N-dicyano-1-κ²C- bis(ethylenediamine-2κ²N,N′)platinum(II)copper(II)], [CuPt(CN)₄(C₂H₈N₂)₂] _n, (I), consists of one-dimensional chains running along the [111] direction. Both Cu and Pt atoms are located on centres of symmetry in an alternating array of [Cu(en)₂]²⁺ (en is ethylenediamine) and [Pt(CN)₄]^2- units. The Pt-C coordination bond distances of 1.985 (4) and 1.995 (4) Å are longer than those of an analogous Ni^II complex. Moreover, due to Jahn-Teller distortion, the axial Cu-N bond distance of 2.562 (5) Å is longer than the equatorial ones of 2.014 (4) and 2.017 (4) Å. © 2006 International Union of Crystallography All rights reserved.

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Synthesis and crystal structures of the flexible Schiff base complex bis(N-1,2-diphenylethyl-salicydenaminato-κ²N,O)copper(II) (methanol)

Akitsu Takashiro, Einaga Yasuaki

Polyhedron 25 ( 5 ) 1089 - 1095 2006.03

ISSN 0277-5387

A new mononuclear copper(II) complex incorporating a bulky Schiff base ligand, bis(N-1,2-diphenylethyl-salicydenaminato-κ²N,O) copper(II) (green form) and its co-crystal containing methanol solvent molecules (brown form) have been synthesized and characterized by X-ray crystallography, XRD, IR and diffuse reflectance spectra in the solid state. This is a rare case in that both solvent free and containing crystals can be isolated and characterized. Both forms adopt a compressed tetrahedral trans-[CuN ₂O₂] coordination geometry with coordination bond angles of trans-N-Cu-N = 157.0(4)° and trans-O-Cu-O = 151.1(3)° for the brown form and trans-N-Cu-N = 141.3(3)° and trans-O-Cu-O = 139.9(2)° for the green form. The methanol solvent molecules force the complex of the brown form to adopt a more planar coordination environment in the solid state. Semi-empirical calculations (ZINDO) revealed the magnitude of the dipole moment of both molecules and that the energy of the green form is 5.7 kJ mol ^-1 higher than that of the brown form. In addition, absorption spectra in various organic solvents were measured and a relationship between absorption spectra and polarity of the solvents is discussed. © 2005 Elsevier Ltd. All rights reserved.

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Structures, magnetic properties, and XPS of cyanide-bridged Nd ^III/Sm^III/Gd^III-Cr^III complexes

Akitsu Takashiro, Einaga Yasuaki

Inorganica Chimica Acta 359 ( 5 ) 1421 - 1426 2006.03

ISSN 0020-1693

Synthesis, structural characterization, and spectroscopic and magnetic properties of three new cyano-bridged 3d-4f bimetallic complexes, Ln ^III(DMF)₄(H₂O)₃Cr^III (CN)₆·nH₂O (Ln = Nd, Sm, Gd), have been described. The Nd-Cr complex crystallizes in the monoclinic P2₁/n space group with the following unit cell parameters: a = 20.063(7) Å, b = 8.967(4) Å, c = 18.023(6) Å, b = 96.12(3)°, V = 3224(2) Å³, and Z = 4. The neodymium (III) ion, which adopts anti-prism eight-coordination environment, is linked to the [Cr^III(CN) ₆]^3- moiety through a bridging cyanide ligand with Nd-N = 2.550(4) Å and Nd-N-C = 164.4(4)°. The variable-temperature (0.5 T at 2-300 K) and variable-field (0-5 T at 2 and 5 K) magnetic measurements reveal that the weak interaction of Gd-Cr complexes differs from that of Nd-Cr and Sm-Cr ones mainly because of the lack of orbital angular momentum. The XPS and diffuse reflectance electronic spectra were also measured to discuss charge transfer transitions concerning π-backdonation from the viewpoint of magneto-optical functions. © 2005 Elsevier B.V. All rights reserved.

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Trans-Bis(4-aminopyridine-κN)bis(succinimidato-κN)copper(II) dihydrate

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 62 ( 3 ) 2006.03

ISSN 1600-5368

The title compound, [Cu(C₄H₄NO₂) ₂(C₅H₆N₂)₂] ·2H₂O has its metal atom in a square-planar trans-[CuN ₄] coordination environment; the Cu^II atom lies on a center of symmetry. Both succinimidate and 4-aminopyridine ligands behave as monodentate ligands, which coordinate through deprotonated imidate and pyridine (not amino) N atoms, respectively. The 4-aminopyridine is the first ligand in such Cu^II complexes containing two different N atoms to take potentially different coordination modes. © 2006 International Union of Crystallography All rights reserved.

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Photomagnetic Langmuir-Blodgett films consisting of azobenzene and Prussian Blue

Yamamoto Takashi, Umemura Yasushi, Sato Osamu, Einaga Yasuaki

Science and Technology of Advanced Materials 7 ( 2 ) 134 - 138 2006.03

ISSN 1468-6996

A photomagnetic organized thin film consisting of an amphiphilic azobenzene, a smectite clay, and Prussian Blue has been prepared by utilizing the Langmuir-Blodgett (LB) method and an ion-exchange reaction. The magnetic LB films were revealed to possess an organized layered structure, and reversible photoisomerization of the azobenzene was observed even in the LB films. Upon photoillumination at 2 K, reversible changes in the magnetization were realized with the value of ca. 11%. This photoswitching in the magnetization is due to changes in the electrostatic field induced by photoisomerization of the azobenzene. A large photoinduced change in the magnetization would be owing to the highly ordered structure of the LB films. In order to verify the correlation between the film structure and photoswitching efficiency, the LB films have been fabricated in other condition. As results, it is confirmed that the packing state of the azobenzene plays an important and crucial role in accomplishment of the highly efficient photomagnetic switching. © 2006 Elsevier Ltd. All rights reserved.

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Electroanalysis of sulfonamides by flow injection system/high-performance liquid chromatography coupled with amperometric detection using boron-doped diamond electrode

Preechaworapun Anchana, Chuanuwatanakul Suchada, Einaga Yasuaki, Grudpan Kate, Motomizu Shoji, Chailapakul Orawon

Talanta 68 ( 5 ) 1726 - 1731 2006.02

ISSN 0039-9140

Sulfonamides (SAs) were electrochemically investigated using cyclic voltammetry at a boron-doped diamond (BDD) electrode. Comparison experiments were carried out using a glassy carbon electrode. The BDD electrode provided well-resolved oxidation, irreversible cyclic voltammograms and higher current signals when compared to the glassy carbon electrode. Results obtained from using the BDD electrode in a flow injection system coupled with amperometric detection were illustrated. The optimum potential from a hydrodynamic voltammogram was found to be 1100 mV versus Ag/AgCl, which was chosen for the HPLC-amperometric system. Excellent results of linear range and detection limit were obtained. This method was also used for determination of sulfonamides in egg samples. The standard solutions of 5, 10, and 15 ppm were spiked in a real sample, and percentage of recoveries was found to be between 90.0 and 107.7. © 2005 Elsevier B.V. All rights reserved.

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Construction of two-dimensional arrays gold nanoparticles monolayer onto boron-doped diamond electrode surfaces

Tian Ru Hai, Rao Tata Narasinga, Einaga Yasuaki, Zhi Jin Fang

Chemistry of Materials 18 ( 4 ) 939 - 945 2006.02

ISSN 0897-4756

A novel method has been developed to immobilize macroscopic two-dimensional arrays of Au nanoparticles (AuNPs) onto the surfaces of boron-doped diamond (BDD) electrodes. These AuNP-modified surfaces are prepared by self-assembly of differently sized colloidal Au particles onto the BDD surfaces. A dense and well-distributed AuNP monolayer onto the BDD surfaces was obtained by pretreating the BDD surface with allylamine by photochemical reaction. These modified surfaces have been characterized by XPS, SEM, and electrochemical cyclic voltammetry (CVs). SEM data indicated that the AuNPs are immobilized and well-dispersed, forming a uniform monolayer on the amine-terminated activated BDD surfaces in two dimensions. Cyclic voltammtric (CV) results indicate that the immobilized AuNPs monolayer onto BDD electrode shows excellent electrochemical properties, implying facile electrochemical communication between the AuNPs monolayer and BDD substrate through the amine linkers. © 2006 American Chemical Society.

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Use of nickel implanted boron-doped diamond thin film electrode coupled to HPLC system for the determination of tetracyclines

Treetepvijit Surudee, Preechaworapun Anchana, Praphairaksit Narong, Chuanuwatanakul Suchada, Einaga Yasuaki, Chailapakul Orawon

Talanta 68 ( 4 ) 1329 - 1335 2006.02

ISSN 0039-9140

The electrochemical analysis of tetracyclines was investigated using nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) by cyclic voltammetry and high performance liquid chromatographic with amperometry. Cyclic voltammetry was used to study the electrochemical oxidation of tetracyclines. Comparison experiments were carried out utilizing as-deposited BDD and glassy carbon electrodes. Ni-DIA electrode provided well-resolved oxidative irreversible cyclic voltammograms and the highest current signals among the electrode studied. High performance liquid chromatography (HPLC) with amperometric detection was also studied. The chromatography was performed using a commercially available Inertsil C18 column, with the mobile phase being: 80% phosphate buffer (pH 2.5)-20% acetonitrile and detected at 1.55 V. The methods were validated over the concentration range 0.05-100 ppm with the overall average recoveries from 83.3 to 102.5% and R.S.D. of less than 10%. The proposed method was further applied to analyse shrimp samples. © 2005 Elsevier B.V. All rights reserved.

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Synthesis of ferrocene-modified phenylazomethine dendrimers possessing redox switching

Suzuki Mana, Nakajima Reina, Tsuruta Masanori, Higuchi Masayoshi, Einaga Yasuaki, Yamamoto Kimihisa

Macromolecules 39 ( 1 ) 64 - 69 2006.01

ISSN 0024-9297

The phenylazomethine dendrimer (DPA) with amino groups at the terminal (end-amine dendrimer) was synthesized by the convergent method without protection from 4,4′-diamino-3,3′,5, 5′-tetramethylbenzophenone (DTB) as the raw material. The amino groups enabled the periphery of the dendrimer (DPA) to be modified by functional molecules, and we succeeded in the synthesis of the end-ferrocene dendrimer (A), which was perfectly modified by the ferrocenes, in one step with high yields. The stepwise metal complexation from the core was also observed in A G2 and A G3. The equilibrium constant K of the terminal imine connected with ferrocnes was determined to be 10 times smaller than that of the N-diphenylmethylene imine (ca. 10⁵ [M^-1]); however, it was strong enough for metal assembling. We found that A G3 showed redox switching by the addition of metal ions. The potential jump of the modified ferrocenes from 0.32 to 0.42 V was observed, when the complexation of Fecl₃, which started from the first layer, reached the third-layer imines next to the ferrocenes. This behavior was reversible based on the encapsulation reversibility and releasing of iron ions. © 2006 American Chemical Society.

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Photo-control of magnetization by photochromic compounds

Einaga Yasuaki

Bulletin of the Chemical Society of Japan 79 ( 3 ) 361 - 372 2006

ISSN 0009-2673

The development of new magnetic materials in which magnetic properties are combined with optical properties has been extensively studied. So far, several photo-responsive molecular solids have been reported. However, the strategies that are necessary to achieve photoinduced switching in a solid state are yet to be clarified. Here, I have focused on composite materials as a novel strategy for realizing such photo-functional magnetic systems. These include the incorporation of organic photochromes into magnetic systems, e.g., photo-controllable magnetic vesicles and LB films containing Prussian blue or iron oxide nanoparticles and azobenzene. © 2006 The Chemical Society of Japan.

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Reversible photocontrol of molecular assemblies of metal complex containing azo-amphiphiles

Einaga Yasuaki, Mikami Rie, Akitsu Takashiro, Li Guangming

Thin Solid Films 493 ( 1-2 ) 230 - 236 2005.12

ISSN 0040-6090

Photo-controllable molecular systems, [M(en)₂][Pt(en) ₂Cl₂](1)₄ (M²⁺=Pt²⁺, Pd²⁺ and en=ethylenediamine), have been designed by the self-assembly of chloride-bridged platinum/palladium complexes and photochromic amphiphiles of the azobenzene derivative, 4-[4-(N-methyl-N-n-dodecylamino)phenylazo]benzene sulfonic acid (designated as compound 1). Reversible structural changes caused by cis-trans photoisomerization of azo groups in compound 1 were observed by alternating illumination of UV and visible light. Visible illumination resulted in the formation of the plate-like structures, whereas UV illumination resulted in fragmentation of the assembling structures. Reversible changes were observed in the electronic states of the chloride-bridged platinum/palladium complexes; the plate-like structures exhibited charge transfer absorption of chloride-bridged platinum complexes and delocalized Pt(II)/Pt(IV) states, while the fragments of the separated complexes exhibited no charge transfer bands. As a consequence, we have discovered that the reversible structural changes in this system could be controlled by photoillumination. © 2004 Elsevier B.V. All rights reserved.

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Syntheses, crystal structures and electronic properties of a series of copper(II) complexes with 3,5-halogen-substituted Schiff base ligands and their solutions

Akitsu Takashiro, Einaga Yasuaki

Polyhedron 24 ( 18 ) 2933 - 2943 2005.12

ISSN 0277-5387

We have systematically investigated the structural features, electronic properties, thermally-induced structural phase transitions and absorption spectra depending on the solvent for ten Cu(II) complexes with 3,5-halogen-substituted Schiff base ligands. Structural characterization of two new complexes, bis(N-R-1-phenylethyl- and N-R,S-2-butyl-5-bromosalicydenaminato- κ²N,O)copper(II), reveals that they afford a compressed tetrahedral trans-[CuN₂O₂] coordination geometry with trans-N-Cu-N = 159.4(2)° and trans-O-Cu-O = 151.7(3)° for the 1-phenylethyl complex and trans-N-Cu-N = 157.9(3)° and trans-O-Cu-O = 151.0(3)° for the 2-butyl one. All the complexes exhibit a structural phase transition by heating in the solid state regardless of their structures at room temperature. The absorption spectra of a series of ten complexes exhibit a slight shift of the d-d band at 16 000-20 000 cm^-1 and remarkable shift of the π-π* band at 24 000-28 000 cm^-1, which suggests that the dipole moment of the solvents presumably affects the conformation of the π-conjugated moieties of the ligands rather than the coordination environment. We have also attempted 'photochromic solute-induced solvatochromism' by a system of bis(N-R-1-phenylethyl-3,5- dichlorosalicydenaminato-κ²N,O)copper(II) and photochromic 4-hydroxyazobenzene in chloroform solution. We successfully observed a change of the d-d and π-π* bands of the complex in the absorption spectra caused by cis-trans photoisomerization of 4-hydroxyazobenzene. © 2005 Elsevier Ltd. All rights reserved.

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Observation of the anisotropic photoinduced magnetization effect in Co-Fe Prussian blue thin films fabricated by using clay Langmuir-Blodgett films as a template

Yamamoto Takashi, Umemura Yasushi, Sato Osamu, Einaga Yasuaki

Journal of the American Chemical Society 127 ( 46 ) 16065 - 16073 2005.11

ISSN 0002-7863

Thin films of cobalt-iron cyanide (Co-Fe Prussian blue) have been fabricated by means of the modified Langmuir-Blodgett (LB) method using a smectite clay mineral (montmorillonite). In this combined method, clay LB films play a template role in the formation of the Co-Fe Prussian blue thin layer. The films were revealed to possess a well-organized structure not only in perpendicular directions to the film surface but also in parallel directions to the film surface. The photoinduced electron transfer from the iron ion to the cobalt through the bridging cyanide in the films occurred at low temperature (8 K), similar to that in the bulk Co-Fe Prussian blue. The films clearly exhibited magnetic anisotropy with regards to the direction of the applied magnetic field. Moreover, the photoinduced magnetization effect in the films was also found to be anisotropic. © 2005 American Chemical Society.

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Pt-implanted boron-doped diamond electrodes and the application for electrochemical detection of hydrogen peroxide

Ivandini Tribidasari A., Sato Rika, Makide Yoshihiro, Fujishima Akira, Einaga Yasuaki

Diamond and Related Materials 14 ( 11-12 ) 2133 - 2138 2005.11

ISSN 0925-9635

Pt-modified diamond electrodes were fabricated for electroanalytical applications by implantation method at 750 keV Pt²⁺ with a dose of 5 × 10¹⁴ cm^{- 2}. The electrochemical behavior has been studied for oxidation of hydrogen peroxide by using cyclic voltammetry and flow injection analysis in phosphate buffer solution (pH 7). The electrode exhibited high catalytic activity and excellent electrochemical stability with a very low background current in comparison to Pt metal electrode. Very low limit of detection, 30 nM (S / N = 3), were examined with RSD of 2.91% (n = 20). These results indicate that metal-implanted method could be a promising method for controlling the electrochemical properties of diamond electrodes. © 2005 Elsevier B.V. All rights reserved.

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Synthesis, crystal structures and electronic properties of Schiff base nickel (II) complexes

Akitsu Takashiro, Einaga Yasuaki

Polyhedron 24 ( 14 ) 1869 - 1877 2005.10

ISSN 0277-5387

Two new mononuclear nickel (II) complexes incorporating Schiff base ligands, bis(N-R-1-phenylethyl- or N-2-propyl-3,5-dichlorosalicydenaminato) nickel (II), have been synthesized and characterized. The former chiral brown paramagnetic complex adopts a compressed tetrahedral [NiN₂O ₂] coordination geometry of Λ(R,R) absolute configuration with the coordination bond angles of N-Ni-N = 116.3(2)°and O-Ni-O = 141.4(2)°. On the other hand, the latter green diamagnetic complex adopts a square planar trans-[NiN₂O₂] coordination geometry. It is revealed that flexible distortion of the [NiN₂O₂] coordination environment and the overall dipole moment of the complexes are affected by both electronic withdrawing Cl-substituents and steric factors of the ligands. A structural phase transition occurs by heating in the solid state for both complexes. Negative solvatochromism relating to d-d and π-π* transitions can be observed, depending on the polarity of the solvents in which these complexes are dissolved. Furthermore, we have attempted to design a supramolecular solvatochromism system induced by a photochromic solute, that is a CHCl₃ solution of the chiral Ni(II) complex and polar 4-hydroxyazobenzene solute. After UV light irradiation, we have successfully observed slight spectral changes of the π-π* bands in absorption and CD spectra due to conformational change of the R-1-phenylethylamine moieties of the chiral ligands. © 2005 Elsevier Ltd. All rights reserved.

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The light-induced excited spin state trapping effect on Ni(dmit) ₂ salt with an Fe(III) spin-crossover cation

Takahashi Kazuyuki, Cui HengBo, Kobayashi Hayao, Einaga Yasuaki, Sato Osamu

Chemistry Letters 34 ( 9 ) 1240 - 1241 2005.09

ISSN 0366-7022

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Photoswitchable magnetic nanoparticles of Prussian blue with amphiphilic azobenzene

Taguchi Minori, Yamada Koji, Suzuki Koji, Sato Osamu, Einaga Yasuaki

Chemistry of Materials 17 ( 17 ) 4554 - 4559 2005.08

ISSN 0897-4756

A novel type of photocontrollable Prussian blue (PB) magnetic nanoparticle has been designed and prepared by using the reverse micelle technique. These magnetic nanoparticles possess a well-organized nanoscale structure. Reversible photoisomerization of azobenzene chromophores realized photoswitching of the magnetization. The photoisomerization of the composite materials was accompanied by a geometrically confined structural change within the reverse micelles, as reflected by changes in the dipole moment and the electrostatic field. As a result, the magnetization values could be switched reversibly by using alternating UV and visible light illumination. © 2005 American Chemical Society.

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Gold-nanoparticle-dispersed boron-doped diamond electrodes for electrochemical oxidation of oxalic acid

Ivandini Tribidasari A., Naono Yasutomo, Nakajima Atsushi, Einaga Yasuaki

Chemistry Letters 34 ( 8 ) 1086 - 1087 2005.08

ISSN 0366-7022

Electrochemical behavior of gold-nanoparticle-dispersed diamond electrodes have been studied for the oxidation of oxalic acid in phosphate buffer solution. Comparison is made with gold, as-deposited diamond and gold-implanted diamond. The electrodes combine the high catalytic activity of gold and the low background current of diamond electrodes. Moreover, the electrodes can overcome the problem of stability as it is found when using other electrodes. Copyright © 2005 The Chemical Society of Japan.

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Photoswitchable magnetic layer-by-layer films consisting of azobenzene derivatives and iron oxide nanoparticles

Suda Masayuki, Miyazaki Yasuo, Hagiwara Yuki, Sato Osamu, Shiratori Seimei, Einaga Yasuaki

Chemistry Letters 34 ( 7 ) 1028 - 1029 2005.07

ISSN 0366-7022

The photoswitchable magnetic thin films have been designed by alternate depositions of bipolar amphiphilic azobenzene and Fe₃O₄ nanoparticles by using the layer-by-layer adsorption technique. In these films, reversible photoisomerizations of the azobenzene chromophore affected the electrostatic interaction between the azobenzene chromophore and the surface of Fe₃O₄ nanoparticles. As a result, we have succeeded in controlling the magnetization of these films by photoillumination at room temperature. Copyright © 2005 The Chemical Society of Japan.

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Electroanalysis of tetracycline using nickel-implanted boron-doped diamond thin film electrode applied to flow injection system

Treetepvijit Surudee, Chuanuwatanakul Suchada, Einaga Yasuaki, Sato Rika, Chailapakul Orawon

Analytical Sciences 21 ( 5 ) 531 - 535 2005.05

ISSN 0910-6340

The electrochemical analysis of tetracycline was investigated using nickel-implanted boron-doped diamond thin film electrode by cyclic voltammetry and amperometry with a flow injection system. Cyclic voltammetry was used to study the electrochemical oxidation of tetracycline. Comparison experiments were carried out using as-deposited boron-doped diamond thin film electrode (BDD). Nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) provided well-resolved oxidation irreversible cyclic voltammograms. The current signals were higher than those obtained using the as-deposited BDD electrode. Results using nickel-implanted boron-doped diamond thin film electrode in flow injection system coupled with amperometric detection are presented. The optimum potential for tetracycline was 1.55 V versus Ag/AgCl. The linear range of 1.0 to 100 μM and the detection limit of 10 nM were obtained. In addition, the application for drug formulation was also investigated. 2005 © The Japan Society for Analytical Chemistry.

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Trans-Bis(2,2-diphenylethylamine-κN)bis(5,5-diphenylhydantoinato- κN³)copper(II) and its chloroform disolvate

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section C: Crystal Structure Communications 61 ( 4 ) 2005.04

ISSN 0108-2701

The crystal structures of the title compounds, [Cu(C₁₅H ₁₁N₂-O₂)₂(C₁₄H ₁₅N)₂] and [Cu(C₁₅H₁₁N ₂O₂)₂(C₁₄H₁₅N) ₂]·2CHCl₃, respectively, have been determined. The red disolvate complex affords a square-planar CuN₄ coordination environment in which the Cu" atom lies on a centre of symmetry. The blue solvent-free complex affords a distorted square-pyramidal CuN₄O coordination environment and adjacent molecules form centrosymmetric dimers. A comparison of the different crystal structures focuses on the role of the solvent molecules in supramolecular assemblies of the copper(II) complexes. © 2005 International Union of Crystallography.

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Diaqua[(1R,2R)-N,N′-bis(3,5-dibromosalicylidene)-cyclohexane-1, 2-diamine-κ⁴O,N,N′,O′]manganese(III) perchlorate dihydrate

Akitsu Takashiro, Takeuchi Yuiri, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 61 ( 4 ) 2005.04

ISSN 1600-5368

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(SP-4-1 )-Bis{aqua(1R,2R)-N,N′-bis(salicylidene)-cyclohexane-1, 2-diy[diamine-κ ⁴O,N,N′,O′]man-ganese(III)}-di-μ-cyano-κ ⁴N

Akitsu Takashiro, Takeuchi Yuiri, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 61 ( 3 ) 2005.03

ISSN 1600-5368

The title compound. [Mn₂Ni(C₂₀H₂₀N ₂O₂)₂(CN)₄(H₂O) ₂], is the first chiral trinuclear complex having an Mn _III-NC-Ni_II-CN-Mn_III unit. A pair of the trans sites of [Ni(CN)₄]_2- links two Mn_III units. The Mn_III ion has a pseudo-octahedral coordination geometry with the four donor atoms of the tetradentate chiral Schiff base forming the equatorial plane, and with a bridging cyanide and an aqua ligand at the axial positions. © 2005 International Union of Crystallography Printed in Great Britain - all rights reserved.

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Self-cleaning particle coating with antireflection properties

Zhang Xin Tong, Sato Osamu, Taguchi Minori, Einaga Yasuaki, Murakami Taketoshi, Fujishima Akira

Chemistry of Materials 17 ( 3 ) 696 - 700 2005.02

ISSN 0897-4756

We report here a self-cleaning particle coating with antireflection (AR) properties. The coatings were prepared by (1) depositing SiO₂ single-layered particle coatings on polyelectrolyte-modified glass substrates through electrostatic attraction, (2) subsequently depositing another layer of TiO₂ nanoparticles through electrostatic attraction, and (3) removing the polymer by calcination at 500 °C. The AR effect of the coatings was studied with transmission spectra collected at normal incidence. The self-cleaning properties of the coatings were studied by the change of the water contact angle on octadodecyldimethylchlorosilane-modified coatings under 1.0 mW cm^-2 ultraviolet light. Both the AR and self-cleaning properties of the coatings were dependent on the concentration of colloidal TiO₂ solution used in the preparation. However, excellent surface wettability of the coatings for water was obtained, independent of the preparation conditions. The experimental findings are discussed in terms of the special structure of the particle coatings.

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The structure, photo-induced magnetization and correlation of the cyano-bridged two-dimensional hetero-bimetallic compounds

Li Guangming, Yan Pengfei, Sato Osamu, Einaga Yasuaki

Journal of Solid State Chemistry 178 ( 1 ) 36 - 40 2005.01

ISSN 0022-4596

Two new 3d-4f cyano-bridged hetero-bimetallic compounds with distinguished two-dimensional honeycomb network structure, {Ln(HP)₂(H ₂O)₃(μ-NC)₃Fe(CN)₃}_n, (Ln=Ce, Nd; HP=4-Hydroxypyridine) were synthesized and crystallographically characterized. A novel photo-induced magnetization phenomenon for {Nd(HP) ₂(H₂O)₃(μ-NC)₃Fe(CN) ₃}_n, was revealed and studied. Furthermore, the correlation between photo-induced magnetization and structure was proposed. © 2004 Elsevier Inc. All rights reserved.

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Use of boron-doped diamond electrode in ozone generation

Park Soo Gil, Kim Gyu Sik, Park Jong Eun, Einaga Yasuaki, Fujishima Akira

Journal of New Materials for Electrochemical Systems 8 ( 1 ) 65 - 68 2005.01

ISSN 1480-2422

Highly boron-doped diamond (BDD) electrode was used as anode for ozone generation system by electrolysis of acidic solution. We have succeeded to generate ozone by using this BDD electrode with high efficiency compared to traditional lead oxide (PbO₂) electrode. Ozone generation by using PbO₂ electrode was gradually decreased due to its structural degradation at continous operating. However, electrochemical and physical properties of the BDD electrode were kept its high stability even after long operation time (>3000 hours) in comparison with PbO₂ electrode. The stability of BDD electrode for long time operation was due to physical and chemical properties of diamond electrode. It was expected that the use of BDD electrode as an anode would make a positive contribution to the electrochemical ozone generation. © New. Mat. Electrochem. Systems.

Bis[(R)-3,5-dichloro-N-(1-phenylethyl)salicylideneaminato-k ²N,O]-copper(ll) and bis[(R)-3-ethoxy-N-(1-phenylethyl) salicylideneaminato-K²N,O]copper(ll)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section C: Crystal Structure Communications 60 ( 12 ) 2004.12

ISSN 0108-2701

The crystal structure of bis[(R)-3,5-dichloro-N-(1-phenyl-ethyl) salicylideneaminato- κ²N, O]-copper(II) and bis[(R)-3-ethoxy-N-(1-phenylethyl)salicylideneaminato-κ²N, O] copper(II) was investigated. The complexes adopt a compressed tetrahedral trans-[CuN₂O₂] coordination geometry. The complexes also differ from one another with respect to the 1-phenylethylamine moieties and the direction of the benzene rings. The structural change was found to be irreversible for both the complexes, though there are no intermolecular hydrogen bonds in the crystals.

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Electronic structures of B 2p and C 2p levels in boron-doped diamond films studied using soft x-ray absorption and emission spectroscopy

Nakamura Jin, Kabasawa Eiki, Yamada Nobuyoshi, Einaga Yasuaki, Saito Daisuke, Isshiki Hideo, Yugo Shigemi, Perera Rupert C C

Physical Review B - Condensed Matter and Materials Physics 70 ( 24 ) 1 - 6 2004.12

ISSN 1098-0121

X-ray absorption (XAS) and emission (XES) spectroscopy near B K and C K edges have been performed on metallic (∼0.1 at. % B, B-diamond) and semiconducting (∼0.03 at. % B and N, BN-diamond) doped diamond films. Both B K XAS and XES spectra show a metallic partial density of states (PDOS) with the Fermi energy of 185.3 eV, and there is no apparent boron-concentration dependence in contrast to the different electric property. In C K XAS spectrum of B-diamond, the impurity state ascribed to boron is clearly observed near the Fermi level. The Fermi energy is found to be almost same with the top of the valence band of nondoped diamond: E_V=283.9 eV. C K XAS of BN-diamond shows both the B-induced shallow level and N-induced deep and broad levels as the in-gap states, in which the shallow level is in good agreement with the activation energy (E_a=0.37 eV) estimated from the temperature dependence of the conductivity; namely, the change in C 2p PDOS of impurity-induced metallization is directly observed. The electric property of this diamond is ascribed mainly to the electronic structure of C 2p near the Fermi level. The observed XES spectra are compared with the discrete variational Xα (DVXα) cluster calculation. The DVXα result supports the strong hybridization between B 2p and C 2p observed in XAS and XES spectra, and suggests that the small amount of boron (≤0.1 at. %) in diamond occupies the substitutional site rather than interstitial site. © 2004 The American Physical Society.

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Reversible photo-switching of the magnetization of iron oxide nanoparticles at room temperature

Mikami Rie, Taguchi Minori, Yamada Koji, Suzuki Koji, Sato Osamu, Einaga Yasuaki

Angewandte Chemie - International Edition 43 ( 45 ) 6135 - 6139 2004.11

ISSN 1433-7851

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Racemic 3,5-dichloro-2-{[(1-phenylethyl)imino]methyl}phenol

Akitsu Takashiro, Takeuchi Yuiri, Einaga Yasuaki

Acta Crystallographica Section C: Crystal Structure Communications 60 ( 11 ) 2004.11

ISSN 0108-2701

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Bis[2-(quinolin-3-yliminomethyl)phenolato-κ ²N,O]-copper(II)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 60 ( 11 ) 2004.11

ISSN 1600-5368

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Electroanalytical application of modified diamond electrodes

Ivandini Tribidasari A., Sato Rika, Makide Yoshihiro, Fujishima Akira, Einaga Yasuaki

Diamond and Related Materials 13 ( 11-12 ) 2003 - 2008 2004.11

ISSN 0925-9635

Metal-modified diamond electrodes were fabricated by using ion implantation method for electroanalytical applications. Nickel and copper ion were implanted at a different film of boron-doped diamond (BDD) with a dose of 5×10¹⁴ cm^-2 for each type of ion. The electrochemical behavior has been studied for glucose oxidation in alkaline media by using cyclic voltammetry and flow injection analysis. Those electrodes exhibited high catalytic activity and excellent electrochemical stability with low background current even after strong ultrasonication in the cleaning process. The results indicate that metal-implanted method could be a promising method for controlling the electrochemical properties of diamond electrodes. © 2004 Elsevier B.V. All rights reserved.

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Bis[(S)-N-(2-butyl)-3,5-dichlorosalicylideneaminato-k ²N,O]copper(II)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 60 ( 11 ) 2004.11

ISSN 1600-5368

The title compound, [Cu(C₁₁H₁₂Cl₂NO) ₂], has a compressed tetrahedral trans-[CuN₂O ₂] coordination environment. The absolute configuration is found to be Δ(S,S) for the crystal examined. The Cu-N bond distances are 1.969 (4) and 1.971 (4) Å, while the Cu-O bond distances are 1.886 (3) and 1.892 (3) Å. The ligands, containing optically active (S)-2-butylamine moieties and electron-withdrawing Cl substituents, lead to an umbrella conformation of the overall molecule. On heating to 387 K, a structural phase transition is observed, probably involving a change in coordination geometry. © 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.

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Bis[2-(phenethyliminomethyl)phenolato-κ²N,O]-copper(II)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 60 ( 11 ) 2004.11

ISSN 1600-5368

The title compound, [Cu(C₁₅H₁₄NO)₂], adopts a stepped conformation and displays a square-planar trans-[CuN ₂O₂] coordination geometry. The asymmetric unit contains two independent half molecules and each Cu atom is located on a center of symmetry. For one molecule, the Cu-N and Cu-O bond distances are 2.013 (2) and 1.893 (2) Å, respectively, while for the other molecule, these distances are 2.008 (2) and 1.896 (2) A. The extended conformation of the phenethylimine pendant groups results in crystal packing formed by weakly aggregated planar molecules. © 2004 International Union of Crystallography Printed in Great Britain -all rights reserved.

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Electric-field-induced conductance switching in FeCo Prussian blue analogues

Sato Osamu, Kawakami Tomoko, Kimura Masanobu, Hishiya Shoko, Kubo Shoichi, Einaga Yasuaki

Journal of the American Chemical Society 126 ( 41 ) 13176 - 13177 2004.10

ISSN 0002-7863

FeCo Prussian blue analogues, which are known as typical molecule-based magnets, exhibited abrupt conductance switching by applying a high electric field as well as by varying the temperature. The current density versus electric field (J-E) curves of FeCo Prussian blue with Rb cations in interstitial sites shows so-called negative resistance effects at electric fields higher than the threshold voltage. This means that the FeCo Prussian blue analogues are multiproperty materials in the sense that their conducting, magnetic, and optical properties can be reversibly controlled by certain external stimuli. Copyright © 2004 American Chemical Society.

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Pt-implanted boron-doped diamond electrodes for electrochemical oxidation of hydrogen peroxide

Ivandini Tribidasari A., Sato Rika, Makide Yoshihiro, Fujishima Akira, Einaga Yasuaki

Chemistry Letters 33 ( 10 ) 1330 - 1331 2004.10

ISSN 0366-7022

Pt-modified diamond electrodes were fabricated for electroanalytical applications by implantation method with a dose of 5 × 10¹⁴ cm^-2. The electrochemical behavior has been studied for oxidation of hydrogen peroxide by using cyclic voltammetry in phosphate buffer solution. With very low background current in comparison to that of Pt metal electrode, the electrode exhibited higher signal to background ratio (≈3.8 times) as well as better electrochemical and physical stability.

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Visible light-induced magnetization change of the cyano-bridged 3d-4f heterobimetallic

Li Guangming, Sato Osamu, Akitsu Takashiro, Einaga Yasuaki

Journal of Solid State Chemistry 177 ( 10 ) 3835 - 3838 2004.10

ISSN 0022-4596

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Modified diamond electrodes for electrolysis and electroanalysis applications

Einaga Yasuaki, Sato Rika, Olivia Herlambang, Shin Dongchan, Ivandini T. A., Fujishima Akira

Electrochimica Acta 49 ( 22-23 SPEC. ISS. ) 3989 - 3995 2004.09

ISSN 0013-4686

The outstanding properties of diamond make it a very attractive material for use in many potential applications. In particular, the superior electrochemical properties of highly boron-doped conductive diamond films, prepared by the chemical vapor deposition (CVD) process, have received attention from electrochemists. This paper reports several diversified applications of boron-doped diamond electrodes; highly sensitive and interference-free microfiber electrodes with over-oxidized polypyrrole modification, integrated electrochemical detector for microchip capillary electrophoresis (CE), and smoothing treatments of micro-polycrystalline surface. Studies have been made of the electrochemical properties of each system and their application in electroanalysis is discussed. © 2004 Elsevier Ltd. All rights reserved.

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Formation of a stable thin sheet of Prussian blue in a clay-organic hybrid film

Umemura Yasushi, Einaga Yasuaki, Yamagishi Akihiko

Materials Letters 58 ( 20 ) 2472 - 2475 2004.08

ISSN 0167-577X

Hybrid films of Prussian blue (PB), clay nanosheets, and alkylammonium cations were prepared by a combined method of Langmuir-Blodgett and self-assembly techniques. The absorbance at 700 nm for the hybrid film increased quadratically up to the 20th layer, and over the 20th layer it increased linearly. This indicated that the hybrid layers were built up in a layer-by-layer way over the 20th layer. X-ray diffraction (XRD) patterns of the film showed that stable thin sheets of PB were formed in the film, and that the in-plane structure of the PB sheet was identical to that of polycrystalline PB. © 2002 Elsevier B.V. All rights reserved.

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Three-dimensional 3d-4f hetero-bimetallic coordination polymers through hydrogen bonds

Li Guangming, Akitsu Takashiro, Sato Osamu, Einaga Yasuaki

Journal of Coordination Chemistry 57 ( 10 ) 855 - 864 2004.07

ISSN 0095-8972

Four cyano-bridged 3d-4f hetero-bimetallic Ln(III)-Fe(III) assemblies, {[Ln(DMF)₄(H₂O)₃(μ-CN)Fe(CN)₅] · H₂O)_n (Ln = Ce (1), Nd (2), Sm (3) and Gd (4); DMF = N,N-dimethylformamide), have been synthesized. X-ray crystallographic analysis of both 3 and 4 reveals three-dimensional network structures resulting from hydrogen bonds in the crystals. With respect to the coordination number on Sm(III) atoms, 3 is different from previously reported structures. Structural comparison indicates that the differences in magnetic properties between 3 and 4 do not derive from structural factors. Mössbauer spectra at both 298 and 10 K reveal that the characteristic quadrupole splitting for low-spin Fe(III) ions (S = 1/2) remains unchanged, indicating that the spin state of Fe(III) ions in 1-4 is not affected by temperature. The magnetic anisotropy derived from the ground states of Ln(III) ions with odd 4fⁿ electrons (n = 1, 3, 5 and 7), ²F_5/2, ⁴I_9/2, ⁶H_5/2 and ⁸S_7/2 for Ce(III), Nd(III), Sm(III) and Gd(III), respectively, dominates the exchange interaction in the Ln(III)-NC-Fe(III) systems.

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Photomagnetic Co-Fe Prussian blue thin films fabricated by the modified Langmuir-Blodgett technique

Yamamoto Takashi, Umemura Yasushi, Sato Osamu, Einaga Yasuaki

Chemistry Letters 33 ( 5 ) 500 - 501 2004.05

ISSN 0366-7022

Co-Fe Prussian blue thin films have been prepared by means of a modified Langmuir-Blodgett technique, in which the hybrid monolayer composed of amphiphiles and clay platelets plays a template role for the formation Co-Fe Prussian blue thin films. Photoinduced magnetization was observed in the thin films as observed in the bulk Co-Fe Prussian blue. To the best of our knowledge, this is the first example of successful formation of Co-Fe Prussian blue thin films, which possess the ordered structure and, in addition, exhibit photoinduced magnetization.

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Trans-Bis(5,5-diphenylhydantoinato)bis-(2-phenylethylamine)copper(II)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 60 ( 5 ) 2004.05

ISSN 1600-5368

The title compound, [Cu(C₁₅H₁₁N₂O ₂)₂(C₈H₁₁N)₂], has its metal atom in a square-planar trans-CuN₄ coordination environment; the Cu^II atom lies on a center of symmetry. The 5,5- diphenylhydantoinate and 2-phenylethylamine ligands behave as monodentate ligands and bind through their N atoms. The crystal structure is stabilized by N-H⋯O=C intermolecular hydrogen bonds [N⋯O = 2.864 (3) Å]. © 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.

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Photoswitchable Magnetic Films

Yamamoto Takashi, Umemura Yasushi, Sato Osamu, Einaga Yasuaki

Chemistry of Materials 16 ( 7 ) 1195 - 1201 2004.04

ISSN 0897-4756

A novel photocontrollable magnetic thin film consisting of amphiphilic azobenzene cations, a smectite clay, and Prussian Blue has been designed and prepared by using the Langmuir-Blodgett method and an ion-exchange reaction. This magnetic thin film possesses a well-organized nanoscale layered structure. Reversible photoisomerization of the azobenzene chromophore realized photoswitching of the magnetization. The changes in the magnetization values were estimated to be ca. 11%. This figure was much larger than our previous system, which contained azobenzene multi-bilayered vesicles in a poly(vinyl alcohol) matrix (J. Am. Chem. Soc. 1999, 121, 3745). These larger changes in the magnetization values are due to the highly ordered structure of the hybrid multilayered films.

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Bis(5-chloro-N-isopropylsalicyldenaminato-κ²/V,O) -copper(II)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 60 ( 4 ) 2004.04

ISSN 1600-5368

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Bis(acetone-κO)bis(N,N′-dimethyl ethylenediamine- κ²N,N′)copper(II) diperchlorate

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section C: Crystal Structure Communications 60 ( 4 ) 2004.04

ISSN 0108-2701

The crystal structure of the bis(acetone-κO)bis(N,N′- dimethylethylenediamine-κ²N,N′)copper(II) diperchorate was investigated. It was found that an elongated octahedral trans-[CuN ₄O₂] coordination geometry was adopted by the complex compound. Two ligands, at the axial sites having O-M-O axial acetone bonds, were also observed in the crystal structure of the metal complex. The results show that the bond length for inplane Cu-N is 2.041(3) Å and that for axial Cu-O is 2.507 (5) Å.

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First observation of photoinduced magnetization for the cyano-bridged 3d-4f heterobimetallic assembly Nd(DMF)₄(H₂O)₃(μ-CN)Fe(CN)₅.H₂O (DMF = N,N-dimethylformamide)

Li Guangming, Akitsu Takashiro, Sato Osamu, Einaga Yasuaki

Hyperfine Interactions 156-157 ( 1-4 ) 143 - 149 2004.03

ISSN 0304-3843

Photoinduced magnetization of the cyano-bridged 3d-4f hetero-bimetallic assembly Nd (DMF)₄(H₂O)₃(μ-CN)Fe(CN)₅.H₂O (1) (DMF = N,N-dimethylformamide) is described in this paper. The χM_T values are enhanced by about 45% after UV light illumination in the temperature range of 5-50 K. We propose that UV light illumination induces a structural distortion in 1. This small structural change is propagated by molecular interactions in the inorganic network. Furthermore, the cooperativity resulting from the molecular interaction functions to increase the activation energy of the relaxation processes, which makes observation of the photoexcited state possible. The flexible network structure through the hydrogen bonds in 1 plays an essential role for the photoinduced phenomenon. This finding may open up a new domain for developing molecule-based magnetic materials. © 2004 Kluwer Academic Publishers.

Synthesis, crystal structures and magnetic properties of two new hetero-bimetallic assemblies

Li Guangming, Akitsu Takashiro, Sato Osamu, Einaga Yasuaki

Journal of Coordination Chemistry 57 ( 3 ) 189 - 198 2004.02

ISSN 0095-8972

Two new cyanide-bridged 3d-4f hetero-dinuclear complexes, namely Ln(DMF)₄(H₂O)₃(μ-CN)Co(CN)₅ · H₂O (Ln=Nd (1) and Gd (2), DMF=N,N-dimethylformamide), were synthesized by the facile reaction of LnCl₃.6H₂O and K₃Co(CN)₆. Characterization includes microanalysis, IR spectrometric identifications, X-ray crystallographic analysis and magnetic properties. Both 1 and 2 crystallize in the centrosymmetric monoclinic space group P2₁/n (No. 14) with Z=4. The lanthanide(III) ions are eight-coordinate in a square-antiprism arrangement, while cobalt(III) ions are six-coordinate in an octahedral environment in each complex. A cyanide bridge links an LN(III) ion to a Co(III) ion. Molecules in the crystal cell of each compound are held together by van der Waals forces and a network of hydrogen bonding. Magnetic analysis shows that antiferromagnetic interactions are observed below 7 K for both 1 and 2, which are attributed to intermolecular interactions between the Ln(III) ions in the network through hydrogen bonds. This series of compounds may be of importance in photo-induced magnetism because of the cyanide bridge between 3d and 4f metals.

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Bis(N,N-dimethylethylenediamine-k²N,N′)-bis(perchlorato- kO)copper(II)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 60 ( 2 ) 2004.02

ISSN 1600-5368

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[N,N′-Bis(2-methoxycarbonyl-3-oxobutylidene)-ethylenediaminato- κ⁴O,N,N′O′]cobalt(II)

Akitsu Takashiro, Iwakura Izumi, Tanaka Hirotaka, Ikeno Taketo, Einaga Yasuaki, Yamada Tohru

Acta Crystallographica Section E: Structure Reports Online 60 ( 2 ) 2004.02

ISSN 1600-5368

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Electrochemical oxidation of Mn²⁺ on boron-doped diamond electrodes with Bi³⁺ used as an electron transfer mediator

Lee Joowook, Einaga Yasuaki, Fujishima Akira, Park Su Moon

Journal of the Electrochemical Society 151 ( 8 ) 2004

ISSN 0013-4651

Electrochemical oxidation of Mn²⁺ with and without the presence of Bi³⁺ was studied using voltammetric and in situ spectro-electrochemical techniques at boron-doped diamond (BDD) electrodes in 1.0 M HClO₄. Electrochemical oxidation of only Mn²⁺ resulted in the formation of mostly MnO₂ with MnO₄ ^- produced as a minor product. The MnO₂ film formed on the electrode surface, which is an inevitable part of Mn²⁺ oxidation, shows a blocking effect on the formation of MnO₄^-, and reduces the overall current efficiency of MnO₄^- production. Higher Mn²⁺ concentrations result in less MnO ₄^- production due to the formation of more MnO ₂. The addition of Bi³⁺ increased the current efficiency of MnO₄^- production. The Bi³⁺ is oxidized to Bi(V), which acts as an electrocatalyst in MnO₄^- production. The Bi(V) oxidizes MnO₂, formed on the electrode surface, to MnO₄^-. This increases the production of MnO ₄^- by removing the blocking film to provide an active electrode (bare BDD) surface, which is available for further Mn²⁺ oxidation. © 2004 The Electrochemical Society. All rights reserved.

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Thermal and Photo-Responsibility of Axial Semi-Coordination Bonds in a Copper(II) Complex

Akitsu Takashiro, Einaga Yasuaki

Bulletin of the Chemical Society of Japan 77 ( 4 ) 763 - 764 2004

ISSN 0009-2673

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Magnetic Vesicles of Amphiphilic Spiropyran Containing Iron Oxide Particles on a Solid State Substrate

Taguchi Minori, Li Guangming, Gu Zhongze, Sato Osamu, Einaga Yasuaki

Chemistry of Materials 15 ( 25 ) 4756 - 4760 2003.12

ISSN 0897-4756

Incorporation of photochromic compounds into magnetic systems is one of the new strategies being implemented to realize the control of magnetic properties by photoillumination. We have designed composite materials comprising iron oxide particles and photochromic spiropyran vesicles as cast films on substrates. Photofunctional magnetic vesicles of amphiphilic spiropyran (SP1822) containing iron oxide particles exhibit superparamagnetic properties at room temperature. Both photoisomerization and photoinduced aggregation of the photoresponsive magnetic vesicles were observed, even without any supporting media such as solvents or polymer matrixes. As a result of the assembly of the vesicles, magnetic dipolar interactions among adjacent iron oxide particles were induced by photoillumination at room temperature, even in the solid state.

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A redetermination of bis(N-methylethyl-enediamine-κ²/N, N′)bis(perchlorato-κO)-copper(II)

Akitsu Takashiro, Einaga Yasuaki

Acta Crystallographica Section E: Structure Reports Online 59 ( 11 ) 2003.11

ISSN 1600-5368

In the title compound, [Cu(ClO₄)2(C₃H ₁₀N₂)₂], the Cu atom is located at a center of symmetry. Despite asymmetric introduction of TV-methyl groups into the ethylenediamine moieties, a second-order Jahn-Teller effect produces a typical semi-coordination trans-[CuN₄(O₂)] environment with long axial Cu - O bonds of 2.569 (2) Å. The Cu - N bond distances are 2.004 (2) and 2.057 (2) Å. © 2003 International Union of Crystallography Printed in Great Britain - all rights reserved.

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Photoinduced magnetization of the cyano-bridged 3d-4f heterobimetallic assembly Nd(DMF)₄(H₂O)₃(μ-CN)Fe(CN) ₅·H₂O (DMF = N,N-dimethylformamide)

Li Guangming, Akitsu Takashiro, Sato Osamu, Einaga Yasuaki

Journal of the American Chemical Society 125 ( 41 ) 12396 - 12397 2003.10

ISSN 0002-7863

Photoinduced magnetization of the cyano-bridged 3d-4f heterobimetallic assembly Nd(DMF)₄(H₂O)₃(μ-CN)Fe(CN)₅·H₂O (1) (DMF = N,N-dimethylformamide) is described in this paper. The χ_MT values are enhanced by about 45% after UV light illumination in the temperature range of 5-50 K. We propose that UV light illumination induces a structural distortion in 1. This small structural change is propagated by molecular interactions in the inorganic network. Furthermore, the cooperativity resulting from the molecular interaction functions to increase the activation energy of the relaxation processes, which makes observation of the photoexcited state possible. The flexible network structure through the hydrogen bonds in 1 plays an essential role for the photoinduced phenomenon. This finding may open up a new domain for developing the molecule-based magnetic materials. Copyright © 2003 American Chemical Society.

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Electrochemical Properties of Ar⁺ Sputtered Polycrystalline Diamond Electrodes with Smoothed Surfaces

Sato Rika, Kondo Takeshi, Shimizu Kenichi, Honda Kensuke, Shibayama Yoshiyuki, Shirahama Keiya, Fujishima Akira, Einaga Yasuaki

Chemistry Letters 32 ( 10 ) 972 - 973 2003.10

ISSN 0366-7022

The initial rough, faceted surfaces of boron-doped conductive polycrystalline diamond electrodes were smoothed by Ar⁺ ion sputtering at very low energy (50 eV). A lower background current was measured at the modified electrodes with a mirror-like appearance than at the initial polycrystalline electrodes. The electrochemical responses to several redox systems also showed a morphological-dependence in some cases. Here, we discuss the electrochemical properties of the diamond electrodes with the smoothed surfaces from the point of view of a novel electrode material.

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An abrupt spin transition based on short S⋯S contacts in a novel Fe(II) complex whose ligand contains a 1,3-dithiole ring

Takahashi Kazuyuki, Kawakami Tomoko, Gu Zhong Ze, Einaga Yasuaki, Fujishima Akira, Sato Osamu

Chemical Communications 9 ( 18 ) 2374 - 2375 2003.09

ISSN 1359-7345

⁵⁷Fe Mössbauer Study on Photoinduced Spin Transition of Ferrocene in Polymer Matrices

Einaga Yasuaki, Kotake Masahiro, Yamada Yasuhiro, Sato Osamu

Chemistry Letters 32 ( 9 ) 846 - 847 2003.09

ISSN 0366-7022

A polymer matrix isolation technique was examined as a potentially novel strategy for realizing optically switchable materials. Not only was a ferricinium ion ([Cp₂Fe^III]⁺) produced, but also was produced an isomer of ferrocene (Cp₂Fe) with high spin Fe^II in a poly(methyl methacrylate) (PMMA) matrix film containing CCl₄ by the photoillumination of ferrocene at low temperature. The high spin state could be maintained for an extended period when the sample was kept below ≈ 130 K. This is the first observation of a photoinduced spin transition for ferrocene. The strategy that we used to achieve the spin transition using optical stimuli may open up many possibilities for the development of new magneto-optical devices.

Magnetization increase of iron oxide by photoinduced aggregation of spiropyran

Einaga Yasuaki, Taguchi Minori, Li Guangming, Akitsu Takashiro, Gu Zhongze, Sugai Takeshi, Sato Osamu

Chemistry of Materials 15 ( 1 ) 8 - 10 2003.01

ISSN 0897-4756

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Control of the magnetic and optical properties in molecular compounds by electrochemical, photochemical and chemical methods

Sato Osamu, Hayami Shinya, Einaga Yasuaki, Gu Zhong Ze

Bulletin of the Chemical Society of Japan 76 ( 3 ) 443 - 470 2003

ISSN 0009-2673

The electrochemical, photochemical and chemical control of the magnetic properties in molecular compounds is described. The preparation of various thin films of CrCr and FeFe Prussian blue on a conducting electrode allowed us to control the magnetic properties by varying the oxidation state of the component metals. The magnetic properties of CrCr Prussian blue show that the critical temperature and coercive field can be drastically modified by electrochemical treatment. That is, the compound, Cr^II
_1.29Cr^III
_0.14 [Cr^III(CN)₆] has ferrimagnetic properties with T_c (critical temperature) = 240 K and H_c (coercive field) = 25 G, while the reduced form, KCr^II
_1.29Cr^III
_0.14 [Cr^II(CN)₆], has T_c = 100 K and H_c = 220 G. Similarly, it was found that the critical temperature of FeFe Prussian blue shifts continuously from paramagnetic to magnetic with T_c = 12 K. These changes can be expressed as K₄Fe^II
₄[Fe^II (CN)₆]₃ (paramagnetic) ⇆ Fe^III
₄[Fe^II(CN)₆]₃ (ferromagnetic, T_c = 4.5 K) + 4 K⁺ + 4e^- and Fe^III
₄[Fe^II(CN)₆]₃ (ferromagnetic, T_c = 4.2 K) + 3Cl^- - 3e^- ⇆ Fe^III
₄[Fe^III(CN)₆] ₃(Cl)₃ (T_c = 12 K). Furthermore, we have discovered that the FeCo Prussian blue and Co valence tautomeric compounds exhibit photo-reversible magnetization effects. The photoinduced magnetization in FeCo Prussian blue is expressed as Na_0.4Co^II-HS
_0.3Co^III-LS [Fe^II(CN)₆] (paramagnetic) ⇆ Na_0.4Co^II-HS
_1.3[Fe^III (CN)₆] (ferrimagnetic, T_c = 26 K and H_c = 6000 G), where HS and LS denote high-spin and low-spin. An example of the photoinduced valence tautomeric behavior is expressed as [Co^III-LS(3,5-dbsq)(3,5-dbcat)(tmeda)] ⇆ [Co^II-HS(3,5-dbsq)₂(tmeda)], where tmeda, 3,5-dbsq and 3,5-dbcat represent N,N,N′,N′-tetramethylethylenediamine, 3,5-di-tert-butyl-1,2-semiquinonate and 3,5-di-tert-butyl-1,2-catecholate, respectively. Additionally, we succeeded in tuning the phase transition temperature by varying the ligand field of the Co ions in the FeCo Prussian blue. Brief comments are also included regarding the first examples of light-induced excited spin state trapping observed in an Fe^III complex, i.e. [Fe^III-LS(pap)₂]ClO₄·H₂O ⇆ [Fe^III-HS(pap)₂]- ClO₄·H₂O (pap = N-2-pyridylmethylidene-2-hydroxy-phenylaminato) and a photoinduced structural change observed in a Cu^II complex, [Cu^II(dieten)₂](BF₄)₂ [dieten = bis(N,N-diethylethylenediamine)].

Reversible photocontrollable magnetic vesicles consisting of azobenzene

Einaga Yasuaki, Yamamoto Takashi, Sugai Takeshi, Sato Osamu

Chemistry of Materials 14 ( 11 ) 4846 - 4850 2002.11

ISSN 0897-4756

Photochromic magnetic vesicles have been designed by intercalation of Prussian blue into a lipid bilayer membrane which consists of azobenzene. Reversible photoisomerization of the solid system realized reversible photocontrol of the magnetic properties. Here, we have synthesized an amphiphile azo moiety containing a long alkyl chain, and we have prepared photochromic magnetic vesicles consisting of only this azo moiety. As a result, the magnetic property change brought about by visible light illumination was estimated to be ca. 13%, which is much larger than the figure achieved for the similar system that we reported previously (∼1%), which contained the double-chain ammonium amphiphile (J. Am. Chem. Soc. 1999, 121, 3745.).

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Homoepitaxial single-crystal boron-doped diamond electrodes for electroanalysis

Kondo Takeshi, Einaga Yasuaki, Sarada Bulusu V., Rao Tata N., Tryk Donald A., Fujishima Akira

Journal of the Electrochemical Society 149 ( 6 ) 2002.06

ISSN 0013-4651

In order to study the properties of single-crystal boron-doped diamond electrodes for electroanalysis, (100) and (111) boron-doped homoepitaxial single-crystal and polycrystalline diamond thin films were deposited by means of microwave plasma-assisted chemical vapor deposition. Features in the cyclic voltammograms (CVs) for aqueous H₂SO₄ supporting electrolyte and Fe(CN)₆^3-/4- in aqueous Na₂SO₄ for polycrystalline electrodes were dominated by behaviour typical of (111) single-crystal facets, rather than (100) facets. Apparent heterogeneous electron-transfer rate constants (k⁰) for various redox systems were estimated with CV simulation at polycrystalline, (111) and (100, off-axis, 4°). Based on comparison with the Marcus model, the behavior of the k⁰ values, except for that of Fe(CN)₆^3-/4-, and indicates apparent outer-sphere electron-transfer, but with a lower density of states compared to glassy carbon or typical metal electrodes. The (111) homoepitaxial film performed better than a polycrystalline film in the cyclic voltammetric detection of serotonin, with signal-to-background ratios of 5 and 2, respectively. Single-crystal diamond may thus be an even more optimal electrode material for electroanalysis than polycrystalline diamond, which has been shown to have superior characteristics as an electrode material.

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Fabrication and electrochemical characterization of boron-doped diamond microdisc array electrodes

Tsunozaki Kentaro, Einaga Yasuaki, Rao Tata N., Fujishima Akira

Chemistry Letters ( 5 ) 502 - 503 2002.05

ISSN 0366-7022

Electrochemical glucose detection using nickel-implanted boron-doped diamond electrodes

Ohnishi Keisuke, Einaga Yasuaki, Notsu Hideo, Terashima Chiaki, Rao Tata Narasinga, Park Soo Gil, Fujishima Akira

Electrochemical and Solid-State Letters 5 ( 3 ) 2002.03

ISSN 1099-0062

Nickel-implanted boron-doped diamond electrodes (Ni-DIA) were fabricated in view of their application for carbohydrate detection. This electrode produced well-defined and reproducible voltammograms for 1 mM glucose in alkaline media. The electrode exhibited excellent electrochemical stability with low background current even after ultrasonic treatment, indicating the strong bonding of nickel with carbon. These results indicate the promising use of Ni-DIA for the detection of carbohydrates and amino acids, and thus, an application of ion implantation as the surface modification method is effective for controlling the electrochemical properties of polycrystalline diamond thin films.

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Factors controlling the electrochemical potential window for diamond electrodes in non-aqueous electrolytes

Yoshimura M., Honda K., Kondo T., Uchikado R., Einaga Y., Rao Tata N., Tryk D. A., Fujishima A.

Diamond and Related Materials 11 ( 1 ) 67 - 74 2002.01

ISSN 0925-9635

The electrochemical behavior of as-deposited diamond was examined in various non-aqueous solvents and supporting electrolytes. The potential for the onset of anodic current was found to be dependent on the nature of the organic solvent, whereas that for the onset of cathodic current was dependent on the type of supporting salt cation. These results indicate that outer-sphere decomposition reactions of the organic solvents are the most important in determining the oxidation potential limit, and those involving cations are the most important in determining the reduction potential limit. These oxidations and reductions were correlated to the HOMO and LUMO energies of the solvents and the supporting electrolyte cations, respectively. The correlations were found to be linear. Electrical double-layer capacitance values were also found to be dependent on the type of electrolyte, and correlations were observed between the capacitance values and the molecular volumes of the solvent as well as between the capacitance and the volumes of the supporting electrolyte cations. The experimental results clearly indicate that the electrical double-layer capacitance values decrease, whereas the thickness of the Helmholz layer increases with increasing volume of the solvated cations. © 2002 Elsevier Science B.V. All rights reserved.

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Radio frequency GDOES depth profiling analysis of a B-doped diamond film deposited onto Si by microwave plasma CVD

Shimizu K., Einaga Y., Ohnishi K., Fujishima A., Habazaki H., Skeldon P., Thompson G. E.

Surface and Interface Analysis 33 ( 1 ) 35 - 40 2002.01

ISSN 0142-2421

Analysis of a boron-doped diamond film, ∼13 μm thick, deposited onto a mirror-finished n-Si(100) substrate using microwave plasma chemical vapour deposition (CVD), demonstrates the suitability of radiofrequency glow discharge optical emission spectroscopy (rf-GDOES) for rapid depth profiling analysis. The distributions of boron and hydrogen are revealed clearly. Intrestingly, the sputtering of the diamond film is accompanied by smoothing of the initial rough, faceted surface, implying that the ridges sputter more rapidly than the valleys during analysis.

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Assembly of highly ordered three-dimensional porous structure with nanocrystalline TiO₂ semiconductors

Meng Q. B., Fu C. H., Einaga Y., Gu Z. Z., Fujishima A., Sato O.

Chemistry of Materials 14 ( 1 ) 83 - 88 2002

ISSN 0897-4756

In this paper, we report on the assembly of a highly ordered three-dimensional porous structure with nanosized crystalline TiO₂ particles by a cooperative assembly method in which the fabrication of the template and the infiltration of the voids of the template are carried out at the same time and the related experimental parameters for the assembly, including temperature, humidity, and concentrations and concentration ratio of the colloid mixture. SEM (scanning electron microscope) images and transmission spectra of these samples demonstrate that these films have a highly ordered three-dimensional structure. The Bragg law was used to calculate the diameter of the spheres of air in the porous TiO₂ structure. A good agreement between the calculated results for the diameter of the spheres of air and those measured by SEM further confirms the high quality of the films fabricated using this simple method. Additionally, based on these experimental results, a detailed mechanism of the simple method is also discussed.

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The electrooxidation of sulfur-containing compounds at boron-doped diamond electrode

Chailapakul O., Aksharanandana P., Frelink T., Einaga Y., Fujishima A.

Sensors and Actuators, B: Chemical 80 ( 3 ) 193 - 201 2001.12

ISSN 0925-4005

The electrooxidation of homocysteine, glutathione (GSH), 2-mercapto ethanesulfonic acid and cephalexin at boron-doped diamond (BDD) electrodes and glassy carbon (GC) electrodes was investigated by cyclic voltammetry. The oxidation of these sulfur-containing compounds exhibited well-defined irreversible responses. This preliminary study has shown that BDD has better sensitivity than GC. Concentration dependence has been studied and indicated the promise of using BDD electrodes for quantitative determination. All of the compounds displayed recognizable oxidation peaks at BDD electrodes at millimolar concentration levels. Scan rate dependence of GSH has been examined. It was shown that there was no adsorption on the surface of the BDD electrode for the low concentration. © 2001 Elsevier Science B.V. All rights reserved.

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Pressure-stabilized low-spin state for binuclear iron(III) spin-crossover compounds

Hayami Shinya, Hosokoshi Yuko, Inoue Katsuya, Einaga Yasuaki, Sato Osamu, Maeda Yonezo

Bulletin of the Chemical Society of Japan 74 ( 12 ) 2361 - 2368 2001.12

ISSN 0009-2673

Binuclear iron(III) spin-crossover complexes with salten ligand [Fe ₂(salten) ₂(L)](BPh ₄) ₂ were synthesized and characterized by single-crystal X-ray diffraction, M6ssbauer spectra, magnetic susceptibilities and electronic spectra, where H ₂salten is a pentadentate ligand derived from salicylaldehyde and 3,3′-diaminodipropylamine and L is a didentate axial ligand (az = azobis(4-pyridine) and cc = 4,4′-vinylenebis(pyridine)). The structures of [Fe ₂(salten) ₂(az)](BPh ₄) ₂ (1) and [Fe ₂(salten) ₂(cc)](BPh ₄) ₂ (2) were determined at both 100 K and 298 K. Crystal data for 1 at 100 K: C ₉₈H ₉₄ O ₄N ₁₀B ₂Fe ₂, monoclinic, space group P2 ₁/c, Z = 2, a = 15.986(2) Å, b = 15.825(2) Å, c = 16.441(2) Å, β = 107.902(2)°, V = 3957.8(8) Å ³. Crystal data for 2 at 100 K: C ₁₀₀H ₉₆ O ₄N ₈B ₂Fe ₂, monoclinic, space group P2 ₁/a, Z = 2, a = 16.4296(8) Å, b = 15.747(1) Å, c = 16.637(1) Å, β = 109.2375(9)° and Z = 2. The complexes 1 and 2 exhibited the spin-crossover behavior depending on temperature within the temperature range of 200 to 350 K, and rapid spin equilibrium behavior was observed by means of M6ssbauer spectroscopy at 293 K. The complexes 1 and 2 also exhibited a pressure-induced spin transition between the rapid spin equilibrium state and low-spin state at 300 K. Such a pressure-induced spin transition has not been reported earlier.

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Varying the optical stop band of a three-dimensional photonic crystal by refractive index control

Gu Zhong Ze, Kubo Shoichi, Qian Weiping, Einaga Yasuaki, Tryk Donald A., Fujishima Akira, Sato Osamu

Langmuir 17 ( 22 ) 6751 - 6753 2001.10

ISSN 0743-7463

A method was developed to continuously adjust the position of the stop band of inverse opal by controlling the refractive index. The inverse opal films were fabricated using a coassembly of monodispersed polystyrene spheres and nanoparticles of silica and titania from aqueous suspensions followed by a calcination treatment. Varying the ratio of silica and titania in the suspensions gave the ability to finely adjust the refractive indices, which as a result changed the stop band.

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Crystal structure and photo-reaction of a new coordination polymer

Gu Zhong Ze, Sato Osamu, Einaga Yasuaki, Kai Masahiro, Iyoda Tomokazu, Fujishima Akira, Hashimoto Kazuhito

Bulletin of the Chemical Society of Japan 74 ( 9 ) 1617 - 1622 2001.09

ISSN 0009-2673

A new photo-responsive coordination polymer of [Ni(en) ₂] ₄[Fe(CN) ₅NO] ₂ [Fe(CN) ₆]·6H ₂O synthesized. In this compound, Ni-CN-Fe forms one-dimensional standing-wave-like chains, onto which photo-functional groups of pentacyanonitrosylferrate(II) are appended. Photo-irradiation with blue light at less than 200 K transformed the pentacyanonitrosylferrate(II) from the ground state to a metastable state, which could be reverted to the original state by irradiation with red light.

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Preparation of graded-morphology diamond thin films

Einaga Yasuaki, Kim Gyu Sik, Ohnishi Keisuke, Park Soo Gil, Fujishima Akira

Materials Science and Engineering B: Solid-State Materials for Advanced Technology 83 ( 1-3 ) 19 - 23 2001.06

ISSN 0921-5107

Graded-morphology diamond thin films were prepared in a single experimental run using a simple technique during the chemical vapor deposition (CVD) process: one end of the substrate was elevated. We showed that the substrate temperature had a profound effect on the morphology and grain size of the as-deposited lightly boron-doped diamond films. We have discussed the morphological dependence of electrochemical properties as one example of the excellent function of the graded film. © 2001 Elsevier Science B.V.

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A novel LIESST iron(II) complex exhibiting a high relaxation temperature

Hayami S., Gu Z. Z., Einaga Y., Kobayasi Y., Ishikawa Y., Yamada Y., Fujishima A., Sato O.

Inorganic Chemistry 40 ( 13 ) 3240 - 3242 2001.06

ISSN 0020-1669

The spin-crossover iron(II) complex [Fe(L)(CN)₂·H₂O (1) has been investigated. Complex 1 has a pentagonal bipyramidal structure which is seven-coordinated, containing an N₃O₂ macrocycle and two CN^- ligands. Water molecules bind the complex by means of hydrogen bonding. It was found that the complex 1 exhibited a light-induced excited spin state trapping (LIESST) effect. The relaxation temperature is above 130 K, which is the highest temperature for LIESST compounds reported so far.

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A study of the crystalline growth of highly boron-doped CVD diamond

Einaga Yasuaki, Kim Gyu Sik, Park Soo Gil, Fujishima Akira

Diamond and Related Materials 10 ( 3-7 ) 306 - 311 2001.03

ISSN 0925-9635

An investigation was made of graded-morphology diamond thin films deposited on Si substrates by use of the microwave plasma chemical vapor deposition (CVD) technique. The preparation of graded diamond thin films not only offers new perspectives into functional materials, but it also gives clues to the growth mechanism of CVD diamond. Although it is clear that the substrate temperature and the deposition time affect the grain size in particular, the difference depending on the boron concentration in the growing process was studied in the present work. As a result, in highly boron-doped (10⁴ ppm) diamond films, the Raman peak which was ascribed to the boron-doping was not observed at the very initial growth stage. However, the crystal growth process was almost irrelevant for the boron-doping quantity. Furthermore, we showed the morphology dependence of electrochemical properties as one example of the excellent functions of the graded-morphology highly boron-doped diamond film. © 2001 Elsevier Science B.V. All rights reserved.

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Fabrication of structured porous film by electrophoresis [2]

Gu Z. Z., Hayami S., Kubo S., Meng Q. B., Einaga Y., Tryk D. A., Fujishima A., Sato O.

Journal of the American Chemical Society 123 ( 1 ) 175 - 176 2001.01

ISSN 0002-7863

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Photo- and dehydration-induced charge transfer processes accompanied with spin transition on CoFe(CN)₅NH₃·6H₂O

Gu Z. Z., Einaga Y., Sato O., Fujishima A., Hashimoto K.

Journal of Solid State Chemistry 159 ( 2 ) 336 - 342 2001

ISSN 0022-4596

The coexistence of different valences of iron and cobalt in cobalt pentacyanoferrate, CoFe(CN)₅NH₃·6H₂O, was confirmed by the infrared spectrum, in which two distinct peaks for the C-N stretch at 2162 cm^-1 and 2117 cm^-1 were assigned to CN in Fe^III-CN-Co^II and Fe^II-CN-Co^III respectively, and by the Mössbauer spectrum, in which Fe^III and Fe^II exhibited doublets with different isomer shifts and different quadrupole splitting. Photo-irradiation of this compound with red light changed the population of these two electronic states due to the internal electron transfer from Fe^II to Co^III. As a result, the ferrimagnetic properties of this pentacyanometalate at low temperature can be changed by photo-irradiation similar to the case of the hexacyanometalate, K_0.2Co_1.4Fe(CN)₆·6.9H₂O reported previously (O. Sato et al., Science 272, 704 (1996)). Moreover, the fraction of these two electronic states in this pentacyanoferrate is sensitive to the number of water molecules, which induces a charge transfer from Co^II and Fe^III. As a result, dehydration increases the fraction of Fe^II-CN-Co^III and causes the compound to be paramagnetic even at low temperature. © 2001 Academic Press.

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Reversible photoinduced switching of magnetic properties at room temperature of iron oxide particles in self-assembled films containing azobenzene

Einaga Y., Gu Z. Z., Hayami S., Fujishima A., Sato O.

Thin Solid Films 374 ( 1 ) 109 - 113 2000.10

ISSN 0040-6090

The use of organized organic assemblies to direct the formation of mesoscopic inorganic structures presents many possibilities in the development of new functional materials. We have designed nano-films containing iron oxide particles, which exhibit magnetic properties at room temperature, and azobenzene by use of an alternate adsorption technique. Photoisomerization of the film was accompanied by a geometrically confined structural change, as reflected by changes in the electrostatic field. As a result, we were able to control the magnetic properties of this film by photoillumination at room temperature.

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First observation of light-induced excited spin state trapping for an iron(III) complex [7]

Hayami Shinya, Gu Zhong Ze, Shiro Motoo, Einaga Yasuaki, Fujishima Akira, Sato Osamu

Journal of the American Chemical Society 122 ( 29 ) 7126 - 7127 2000.07

ISSN 0002-7863

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Hetero metal spin-crossover complex with LIESST iron(II) building block

Hayami Shinya, Gu Zhonge, Einaga Yasuaki, Fujishima Akira, Sato Osamu

Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals 343 2000

ISSN 1058-725X

LIESST iron(II) spin-crossover mononuclear complex [Fe(L)(CN)₂]·H₂O (1) (L is Schiff-base macrocylic ligand derived from the condensation of 2,6-diacetylpyridine with 3,6-dioxaoctane-1,8- diamine) with macro ring and two CN^- bridging ligands in complex 1 can coordinate to other metal compounds, it is possible to build one-dimensional molecular-based photo-magnets. We have synthesized [Fe(L)(CN)₂][Mn(hfac)₂] (2) and investigated it by using magnetic susceptibility, Mossbauer spectra and IR spectra measurements. The complex 2 exhibits spin-crossover behavior (T_1/2=110 K) on the moieties of the iron sites.

Magnetic properties and optical control of electrochemically prepared iron-chromium polycyanides

Ohkoshi Shin Ichi, Einaga Yasuaki, Fujishima Akira, Hashimoto Kazuhito

Journal of Electroanalytical Chemistry 473 ( 1 ) 245 - 249 1999.09

ISSN 0022-0728

The magnetic properties and photo-magnetic effects of the electrochemically prepared metal polycyanide film, Fe_1.5^II[Cr^III(CN)₆]·7.5H₂O, were investigated. Magnetization measurements showed that it was a ferromagnet (parallel spin ordering) having a T_c = 21 K. The spontaneous magnetization decreased optically by the photoexcitation of the intervalence transfer (IT) band between Fe^II and Cr^III. This optically reduced magnetization persisted for a period of several days at 5 K after turning off the light. ⁵⁷Fe Moessbauer experiments showed that the spin state of iron did not change but the strength of a ferromagnetic interaction between Fe^II and Cr^III decreased after the irradiation, forming a paramagnetic metastable state. This metastable state returned to the original state above 40 K, showing that the magnetization of this compound can be controlled reversibly by the combination of optical and thermal methods.

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Photofunctional vesicles containing prussian blue and azobenzene

Einaga Y., Sato O., Iyoda T., Fujishima A., Hashimoto K.

Journal of the American Chemical Society 121 ( 15 ) 3745 - 3750 1999.04

ISSN 0002-7863

The intercalation of inorganic materials into organized organic assemblies presents many opportunities for the development of new functional materials with superior physicochemical properties. We have designed a composite material comprising Prussian blue intercalated into photoresponsive organic molecules (azobenzene-containing multibilayer vesicles). Photoisomerization in the solid system was achieved by diluting the azobenzene-containing bilayer membrane in a poly(vinyl alcohol) matrix. The photoisomerization of the film was accompanied by a geometrically confined structural change within the vesicles, as reflected by changes in the dipole moment and electrostatic field. As a result, we were able to control the magnetic properties of this material by photoillumination.

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Photoinduced long-range magnetic ordering of a cobalt-iron cyanide

Sato O., Einaga Y., Fujishima A., Hashimoto K.

Inorganic Chemistry 38 ( 20 ) 4405 - 4412 1999

ISSN 0020-1669

Two kinds of cobalt-iron cyanides (Rb_0.66Co_1.25[Fe(CN)₆]·4.3H₂O and Co_1.5[Fe(CN)₆]·6H₂O) with different electronic structures have been investigated to understand the photoinduced long-range magnetic ordering. Rb_0.66Co_1.25[Fe(CN)₆]·4.3H₂O produces a photomagnetic effect, whereas Co_1.5[Fe(CN)₆]·6H₂O does not respond to light. FT-IR and Mossbauer studies revealed that their oxidation states are expressed as Rb_0.66Co^III_0.84Co^II _0.41-[Fe_II(CN)₆] and Co^II_1.5[Fe^III(CN)₆], respectively. The difference in the oxidation states of the metal atoms in these two compounds has been explained by the Co coordination with H₂O or CN ligands. In the case of Rb_0.66Co_1.25[Fe(CN)₆]·4.3H₂O, more CN ligands are involved in coordination than expected in the case of Co_1.5[Fe(CN)₆]· 6H₂O. A charge-transfer (CT) band from Fe^II to Co^III is observed at around 550 nm for Rb^0.66Co^1.25[Fe(CN)₆]· 4.3H₂O. The magnetism of Rb_0.66Co_1.25[Fe(CN)₆]·4.3H₂O changed from paramagnetic to ferrimagnetic due to the CT from Fe^II to Co^III when illuminated at low temperature. The Curie temperature after illumination was 22 K. This metastable state was stable for more than several days at 5 K. The metastable state was restored back to its original one when the sample was heated to 120 K. It is considered that the interconversion proceeded via a pronounced domain formation. © 1999 American Chemical Society.

Local structure of a trapped photoexcited state of a Fe-Co cyanide studied by x-ray-absorption fine-structure spectroscopy

Yokoyama Toshihiko, Kiguchi Manabu, Ohta Toshiaki, Sato Osamu, Einaga Yasuaki, Hashimoto Kazuhito

Physical Review B - Condensed Matter and Materials Physics 60 ( 13 ) 9340 - 9346 1999

ISSN 0163-1829

The local structure of a trapped photoexcited state of a Fe-Co cyanide magnetic material, Na_0.4Co_1.3Fe(CN)₆·5H₂O, was investigated by Fe and Co K-edge x-ray-absorption fine-structure spectroscopy. The excited state was prepared by visible-light irradiation at 36 K. In order to obtain detailed structural information, temperature dependence of the local structure was also studied without light irradiation. The Fe-C distance shows almost no change by light irradiation (1.92 Å before and after irradiation), while the average Co-N/O distance is noticeably elongated (1.94 and 2.08 Å before and after irradiation, respectively). This phase transformation is caused by the charge transfer from the Fe^II(S=0)·CN-Co^III(S=0) configuration to Fe^III(S =1/2)-CN-Co^II(S=3/2). The local structure of the trapped photoexcited state was found to be identical with that of the high-temperature phase, although the high-temperature phase was created much more effectively by light irradiation than thermal activation. ©1999 The American Physical Society.

Mössbauer study on characterization of Co[Fe(CN)₅NH₃] · xH₂O

Einaga Y., Gu Z. Z., Kobayashi Y., Sato O., Iyoda T., Ambe F., Hashimoto K., Fujishima A.

Hyperfine Interactions 116 ( 1-4 ) 159 - 166 1998

ISSN 0304-3843

External magnetic field effect on the photoinduced magnetization in a cobalt iron cyanide

Einaga Yasuaki, Ohkoshi Shin Ichi, Sato Osamu, Fujishima Akira, Hashimoto Kazuhito

Chemistry Letters ( 7 ) 585 - 586 1998

ISSN 0366-7022

We studied the external magnetic field effects on the photoinduced magnetization of a cobalt iron cyanide, K_0.4Co_1.3[Fe(CN)₆]·5H₂O. Photoinduced magnetization value was increased ca. 20 % at maximum under the magnetic field of 50000 G at 5 K. In addition, in the ferrimagnetic region (T < T_c = 26 K), the external magnetic field accelerated the rate of photoinduced spin generation. Those data suggest that external magnetic field increases magnetic interaction between the excited state and spin clusters.

Cation-driven electron transfer involving a spin transition at room temperature in a cobalt iron cyanide thin film

Sato O., Einaga Y., Iyoda T., Fujishima A., Hashimoto K.

Journal of Physical Chemistry B 101 ( 20 ) 1997.05

ISSN 1089-5647

The electronic structure of a cobalt iron cyanide thin film, Na_0.4Co_1.3[Fe(CN)₆]5H₂O, was switched from Fe^III(low spin)-CN-Co^II(high spin) to Fe^II(low spin)-CN-Co^III(low spin) by exchanging cations in interstitial sites from Na⁺ to K⁺. The reverse process was also induced by replacing Na⁺ with K⁺. That is, the alkali cations in the interstitial sites dominate the electronic and spin states of the host compound. This type of switching phenomenon can be achieved by choosing a compound with both electronic degeneracy and zeolitic properties.

Reversible photoinduced magnetization

Sato O., Einaga Y., Iyoda T., Fujishima A., Hashimoto K.

Journal of the Electrochemical Society 144 ( 1 ) 1997.01

ISSN 0013-4651

Reversible photoinduced magnetization was observed in a cobalt iron cyanide thin film. Magnetic properties of the prussian blue analog, K_0.4Co_1.3[Fe(CN)₆] ·5H₂O, can be switched between ferrimagnetic and paramagnetic by visible and near-IR light illumination.The critical temperature after illumination was about 26 K. This material, obtained via an electrochemical route in the form of thin films on an electrode, provides a new system whose magnetic properties can be controlled by both photochemical and electrochemical redox reactions.

Mossbauer study on photochemistry of ferrocene isolated in low- temperature matrix

Einaga Y., Yamada Y., Tominaga T.

Journal of Radioanalytical and Nuclear Chemistry 218 ( 1 ) 97 - 100 1997

ISSN 0236-5731

Unstable novel species produced by photolysis of ferrocene (Cp₂Fe) isolated in low-temperature matrix were studied by means of the ⁵⁷Fe Mossbauer spectroscopy. On the UV-irradiation of ⁵⁷Fe-enriched ferrocene co-condensed with CCl₂ in low-temperature N₂ matrix (20 K), unknown high spin ferrous species (I.S. = 0.90 ± 0.02 mm/s), Q.S. = 1.94 ± 0.02 mm/s) were produced as well as ferricinium ion [Cp₂Fe]⁺ (I.S. = 0.52 ± 0.01 mm/s, Q.S. = 0.0 mm/s). On the annealing, these photoproducts disappeared to reform ferrocene by the reverse reaction in the matrix. The mechanisms of the photochemical reaction were discussed.

Access to Document (DOI)

Electronic states of cobalt iron cyanides studied by ⁵⁷Fe Mössbauer spectroscopy

Einaga Yasuaki, Sato Osamu, Iyoda Tomokazu, Kobayashi Yoshio, Ambe Fumitoshi, Hashimoto Kazuhito, Fujishima Akira

Chemistry Letters ( 4 ) 289 - 290 1997

ISSN 0366-7022

The electronic states of cobalt iron cyanides were observed using ⁵⁷Fe Mössbauer. It was revealed that Prussian blue analogs Co_1.5[Fe(CN)₆]6H₂O and K_0.5Co_1.25[Fe(CN)₆]3.6H₂0 have Fe^III(low spin) and Fe^II(low spin), respectively, at both room temperature and 4 K. In Co_1.5[Fe(CN)₆]6H₂O, a magnetic hyperfine interaction was observed at low temperature. Moreover, the Mössbauer spectra provided clear evidence for an internal electron transfer from Fe^II to Co^III in K_0.5Co_1.25[Fe (CN)₆]3.6H₂O by red light illumination at low temperature.

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