Details of a Researcher - Einaga, Yasuaki

Papers - Einaga, Yasuaki

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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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