Details of a Researcher - Einaga, Yasuaki

Papers - Einaga, Yasuaki

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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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