Papers - YAMAMOTO Masahiro
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Yuko YOKOYAMA, Takaaki NAGAI, Akimitsu ISHIHARA, Masahiro YAMAMOTO, Kohei MIYAZAKI, Takeshi ABE, Kenji KANO
Electrochemistry 90 ( 10 ) 103003 - 103003 2022.9
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Reciprocal Sum Expression for Steady-state Kinetics —Enzyme Reactions and Voltammetry— Reviewed
Yuko YOKOYAMA, Masahiro YAMAMOTO, Kohei MIYAZAKI, Takeshi ABE, Kenji KANO
Electrochemistry 90 ( 10 ) 103002 - 103002 2022.7
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The use of the reference electrode equipped with an ionic liquid salt bridge in electrochemistry of ionic liquids: A convenient way to align the formal potentials of redox reactions in ionic liquids based on the standard hydrogen electrode scale Reviewed
Takashi Kakiuchi, Shota Domae, Taishi Miyadi, Kaito Kibi, Masahiro Yamamoto
ELECTROCHEMISTRY COMMUNICATIONS 126 2021.5
Joint Work
Publisher：ELSEVIER SCIENCE INC
A hydrophobic ionic liquid composed of a cationic and anionic species having similar magnitudes of hydrophobicity and mobilities can work as a salt bridge separating two electrolyte solutions, that is, the sample solution and the inner solution of the reference electrode. A few examples of superiority of this ionic liquid salt bridge (ILSB) over the traditional salt bridges made of a concentrated aqueous KCl solution have been demonstrated. The present study is a further extension of the use of ILSB to voltammtery of the redox reactions of ferrocene/ferrocenium and cobaltocene/cobaltocenium couples in an ionic liquid, tributyl(2-methoxyethyl) phosphonium bis(pentafluoroethanesulfonyl) amide ([TBMOEP][C2C2N]), which is also used as the ILSB. The obtained mid-point potentials (Ems) are converted straightforwardly to those referred to the standard hydrogen electrode (SHE). A comparison of Em (SHE) values of the two redox couples in [TBMOEP][C2C2N] with the corresponding values in molecular solvents suggests that the environment given by [TBMOEP][C2C2N] to the two redox reactions is macroscopically similar to that of methanol.
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Single ion activity coefficients of chloride ions in aqueous sodium chloride and magnesium chloride estimated potentiometrically based on ionic liquid salt bridge at 298 K Invited Reviewed
Takashi Kakiuchi, Masaki Hisazumi, Yasufumi Moriyama, Masahiro Yamamoto
Electrochemistry Communications 124 106953 2021.3
Joint Work
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Tailored Photoluminescence Properties of Ag(In,Ga)Se2 Quantum Dots for Near-Infrared In Vivo Imaging Reviewed
Tatsuya Kameyama, Hiroki Yamauchi, Takahisa Yamamoto, Toshiki Mizumaki, Hiroshi Yukawa, Masahiro Yamamoto, Shigeru Ikeda, Taro Uematsu, Yoshinobu Baba, Susumu Kuwabata, Tsukasa Torimoto
ACS Applied Nano Materials 3 ( 4 ) 3275 - 3287 2020.2
Joint Work
Publisher：American Chemical Society (ACS)
Copyright © 2020 American Chemical Society. Multinary semiconductor quantum dots (QDs) that have less toxicity and show near-infrared light responsivity have attracted much attention for in vivo bioimaging. In this study, we controlled the optical properties of Ag-In-Se QDs by modulating the nonstoichiometry and the degree of Ga3+ doping. Precise tuning of the Ag/In ratio of Ag-In-Se QDs enabled a sharp band-edge emission to emerge without broad defect-site emission. Ga3+ doping into Ag-In-Se (AIGSe) QDs enlarged their energy gap, resulting in a blue shift of the band-edge PL peak from from 890 to 630 nm. The band-edge PL intensity was remarkably enlarged by surface coating with a thin GaSx shell followed by treatment with trioctylphosphine, the highest PL yield being 38% for the PL peak at 800 nm. Thus-obtained QDs were successfully used as near-IR PL probes for three-dimensional in vivo bioimaging in which the wavelengths of excitation and detection lights could be selected in the first biological window, and then the signals were clearly detected from AIGSe@GaSx core-shell QDs injected into biological tissues by ca. 5 mm in depth.
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Effects of Contact Angle and Flocculation of Particles of Oligomer of Tetrafluoroethylene on Oil Foaming Reviewed International coauthorship
Ryo Murakami, Syuji Kobayashi, Manami Okazaki, Alexander Bismarck, Masahiro Yamamoto
Frontiers in Chemistry 6 2018.9
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Treatment of oral cancer using magnetized paclitaxel Reviewed International coauthorship
Rina Nakakaji, Masanari Umemura, Kenji Mitsudo, Jeong-Hwan Kim, Yujiro Hoshino, Itaru Sato, Takatsugu Masuda, Masahiro Yamamoto, Mitomu Kioi, Toshiyuki Koizumi, Takayuki Fujita, Utako Yokoyama, Masaki Iida, Motohiko Sato, Hiroshi Sato, Shoko Murofushi, Sayaka Shibata, Ichio Aoki, Haruki Eguchi, Iwai Tohnai, Yoshihiro Ishikawa
Oncotarget 9 ( 21 ) 15591 - 15605 2018.3
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A model of the potential-dependent adsorption of charged redox-active species at the electrode surface Reviewed
Yuki Kitazumi, Osamu Shirai, Masahiro Yamamoto, Kenji Kano
Electrochimica Acta 259 542 - 551 2018.1
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Treatment of oral cancer using magnetized paclitaxel Reviewed International coauthorship
R. Nakakaji et al.
Oncotarget 2018
Joint Work
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Electrochemical Sensing of Neurotoxic Agents Based on Their Electron Transfer Promotion Effect on an Au Electrode Reviewed
Hiroshi Shimada, Shiori Noguchi, Masahiro Yamamoto, Katsuhiko Nishiyama, Yusuke Kitamura, Toshihiro Ihara
Analytical Chemistry 89 ( 11 ) 5743 - 5748 2017.6
Joint Work
Publisher：AMER CHEMICAL SOC
© 2017 American Chemical Society. An electrochemical molecular sensor based on a new principle is reported. Nereistoxin (NRT, 4-N,N-dimethylamino-1,2-dithiolane), a naturally occurring neurotoxin (nicotinic acetylcholine receptor agonist), was adsorbed on an Au electrode via Au-S covalent bonding and accelerated the electron transfer between the electrode and the marker, ferricyanide anion. The contrast between the electrochemical responses obtained with the bare and NRT-modified Au electrodes was more pronounced at a low ionic strength of the supporting electrolyte, KCl. In the presence of 1 mM KCl, almost a 0/1 contrast between the signals was obtained through electrostatic interaction between the protonated tertiary amino group of NRT and the anionic ferricyanide ion. No current was observed with an electrode modified with mercaptopropionic acid. An unusually low ionic strength thickened the electric double layer to the degree where current was not observed with the bare electrode. The effect of the electrostatic concentration of the marker ion becomes obvious under such conditions. Commercially available NRT-related pesticides such as Cartap and Bensultap were also detected using the same format after pretreatments by hydrolysis/reduction. The present sensing method was successfully applied to human serum with satisfactory sensitivity.
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Electrostatic roles in electron transfer from [NiFe] hydrogenase to cytochrome c<inf>3</inf> from Desulfovibrio vulgaris Miyazaki F Reviewed
Yu Sugimoto, Yuki Kitazumi, Osamu Shirai, Koji Nishikawa, Yoshiki Higuchi, Masahiro Yamamoto, Kenji Kano
Biochimica et Biophysica Acta - Proteins and Proteomics 1865 ( 5 ) 481 - 487 2017.5
Joint Work
Publisher：ELSEVIER SCIENCE BV
© 2017 Elsevier B.V. Electrostatic interactions between proteins are key factors that govern the association and reaction rate. We spectroscopically determine the second-order reaction rate constant (k) of electron transfer from [NiFe] hydrogenase (H2ase) to cytochrome (cyt) c3 at various ionic strengths (I). The k value decreases with I. To analyze the results, we develop a semi-analytical formula for I dependence of k based on the assumptions that molecules are spherical and the reaction proceeds via a transition state. Fitting of the formula to the experimental data reveals that the interaction occurs in limited regions with opposite charges and with radii much smaller than those estimated from crystal structures. This suggests that local charges in H2ase and cyt c3 play important roles in the reaction. Although the crystallographic data indicate a positive electrostatic potential over almost the entire surface of the proteins, there exists a small region with negative potential on H2ase at which the electron transfer from H2ase to cyt c3 may occur. This local negative potential region is identical to the hypothetical interaction sphere predicted by the analysis. Furthermore, I dependence of k is predicted by the Adaptive Poisson–Boltzmann Solver considering all charges of the amino acids in the proteins and the configuration of H2ase/cyt c3 complex. The calculation reproduces the experimental results except at extremely low I. These results indicate that the stabilization derived from the local electrostatic interaction in the H2ase/cyt c3 complex overcomes the destabilization derived from the electrostatic repulsion of the overall positive charge of both proteins.
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Electrochemical Sensing of Neurotoxic Agents Based on Their Electron Transfer Promotion Effect on an Au Electrode Reviewed
Hiroshi Shimada, Shiori Noguchi, Masahiro Yamamoto, Katsuhiko Nishiyama, Yusuke Kitamura, Toshihiro Ihara
Anal. Chem. 2017
Joint Work
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Magnetic metal complex-conducting copolymer core-shell nanoassemblies for single-drug anticancer platform Reviewed
Jeong-Hwan Kim, Haruki Eguchi, Masanari Umemura, Itaru Sato, Shigeki Yamada, Yujiro Hoshino, Takatsugu Masuda, Ichio Aoki, Kazuo Sakurai, Masahiro Yamamoto and Yoshihiro Ishikawa
NPG(Nature Publishing Group) Asia Materials 2017
Joint Work
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“Electrostatic roles in electron transfer from [NiFe] hydrogenase to cytochrome c3 from Desulfovibrio vulgaris Miyazaki F Reviewed
Yu Sugimoto, Yuki Kitazumi, Osamu Shirai, Koji Nishikawa, Yoshiki Higuchi, Masahiro Yamamoto, Kenji Kano
BBA - Proteins and Proteomics 2017
Joint Work
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Magnetic metal-complex-conducting copolymer core-shell nanoassemblies for a single-drug anticancer platform Reviewed
Jeong Hwan Kim, Haruki Eguchi, Masanari Umemura, Itaru Sato, Shigeki Yamada, Yujiro Hoshino, Takatsugu Masuda, Ichio Aoki, Kazuo Sakurai, Masahiro Yamamoto, Yoshihiro Ishikawa
NPG Asia Materials 9 ( 3 ) 2017
Joint Work
Nanoparticulate agents for magnetic drug delivery systems (DDSs) have extensive applications in targeted drug delivery, contrast imaging and therapeutics. However, no simple synthetic method for magnetic DDS agents has been developed without the need to add magnetic nanoparticles. Here, we describe the one-step fabrication of 'all-in-one' magneto-assemblies using an 'inorganic-metal-salt-free' method, involving spontaneous self-assembly of the water-insoluble prodrug μ-oxo-bis(N,N0-ethylenebis (salicylideniminato)iron) [Fe(salen)] (magnetic core) with polypyrrole (PPy)-b-polycaprolactone (PCL) smart diblock copolymers. In the system, PCL serves as a heat-responsive core scaffold, and PPy serves as an electronic core-size controller and pH-responsive shell. This core-shell nanocomposite has a high-loading capacity (∼90%), and the core size is tunable by incorporating albumin or gum Arabic as bio-coating agents, which also provide colloidal stability, biocompatibility and thermo-stability. Fe(salen), which has intrinsic antitumor activity, also has ubiquitous magnetic properties, which are dramatically enhanced in these molecular assemblies with magnetic coupling. Moreover, these multifunctional nanoassemblies can be delivered magnetically, can serve as magnetic resonance imaging contrast agents, can generate magneto-hyperthermal effects and can enable magnetic field-triggered release of Fe(salen) molecules under acidic conditions.
DOI： 10.1038/am.2017.29
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Potentiometric coulometry using a liquid-film-modified electrode as a reversible surface-confined system Reviewed
Ryutaro Katsube, Yuki Kitazumi, Osamu Shirai, Masahiro Yamamoto, Kenji Kano
Journal of Electroanalytical Chemistry 780 114 - 118 2016.11
Joint Work
© 2016 Elsevier B.V. A reversible surface-confined system for potentiometric coulometry studies was fabricated by the deposition of a liquid film on an electrode surface, and the system was used to detect charge accumulation due to the peroxidase (POD)-catalyzed reduction of H2O2. The components of the liquid film were 1-ethyl-3-methylimidazolium bis(nonafluorobutanesulfonyl)imide as the electrolyte, dibutyl phthalate as the medium, and ferrocene as the redox-active mediator. When the thickness of the liquid film was less than that of the diffusion layer in the minimum potential step of the apparatus, a symmetric voltammogram, according to the Nernst equation, was recorded. The reduction of H2O2 by POD was carried out on the liquid-film-modified electrode and studied by potentiometric coulometry. The addition of H2O2 shifts the electrode potential positively, due to the oxidation of ferrocene. The change in the potential is in agreement with the Nernst equation. Thus, potentiometric coulometry, carried out on the liquid-film-modified electrode, enables the determination of the substrate without the requirement of a calibration curve.
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Current stage and perspectives of pH measurements by use of ionic liquid salt bridge
Takashi Kakiuchi, Masahiro Yamamoto
Bunseki Kagaku 65 ( 4 ) 181 - 191 2016.5
Joint Work
© 2016 The Japan Society for Analytical Chemistry. The use of a moderately hydrophobic ionic liquid for a salt bridge allows us to accurately measure pH of low ionic strength aqueous solutions, which was not possible by use of a salt bridge based on a concentrated aqueous potassium chloride solution (KClSB). When a sample solution does not contain hydrophobic ions, the ionic liquid salt bridge is promising also in pH measurements of high ionic-strength samples. That ionic liquid salt bridge enables us to measure the single-ion activities of not only hydrogen ions, but also other ionic species gives new perspectives in studying electrolyte solutions, not limited by the traditional framework set by the KClSB.
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Understanding of the Effects of Ionic Strength on the Bimolecular Rate Constant between Structurally Identified Redox Enzymes and Charged Substrates Using Numerical Simulations on the Basis of the Poisson-Boltzmann Equation Reviewed
Yu Sugimoto, Yuki Kitazumi, Osamu Shirai, Masahiro Yamamoto, Kenji Kano
Journal of Physical Chemistry B 120 ( 12 ) 3122 - 3128 2016.3
Joint Work
Publisher：AMER CHEMICAL SOC
© 2016 American Chemical Society. To understand electrostatic interactions in biomolecules, the bimolecular rate constants (k) between redox enzymes and charged substrates (in this study, redox mediators in the electrode reaction) were evaluated at various ionic strengths (I) for the mediated bioelectrocatalytic reaction. The k value between bilirubin oxidase (BOD) and positively charged mediators increased with I, while that between BOD and negatively charged mediators decreased with I. The opposite trend was observed for the reaction of glucose oxidase (GOD). In the case of noncharged mediators, the k value was independent of I for both BOD and GOD. These results reflect the electrostatic interactions between the enzymes and the mediators. Furthermore, we estimated k/k° (k° being the thermodynamic rate constant) by numerical simulation (finite element method) based on the Poisson-Boltzmann (PB) equation. By considering the charges of individual atoms involved in the amino acids around the substrate binding sites in the enzymes, the simulated k/k° values well reproduced the experimental data. In conclusion, k/k° can be predicted by PB-based simulation as long as the crystal structure of the enzyme and the substrate binding site are known. (Graph Presented).
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Potentiometric coulometry using a liquid-film-modified electrode as a reversible surfaceconfined system”, J. Electroanal. Chem. 2016, 780, Reviewed
Ryutaro Katsube, Yuki Kitazumi, Osamu Shirai, Masahiro Yamamotob, Kenji Kano
J. Electronal. chem. 2016
Joint Work
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Strength on the Bimolecular Rate Constant between Structurally Identified Redox Enzymes and Charged Substrates Using Numerical Simulations on the Basis of the Poisson-Boltzmann Equation Reviewed
Masahiro Yamamoto, and Kenji Kano
J. Phys. Chem. 2016
Joint Work
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Prediction of the Standard Gibbs Energy of Transfer of Organic Ions Across the Interface between Two Immiscible Liquids Reviewed
Toshiyuki Osakai, Yasuhiro Naito, Kazuo Eda, Masahiro Yamamoto
Journal of Physical Chemistry B 119 ( 41 ) 13167 - 13176 2015.10
Joint Work
© 2015 American Chemical Society. The non-Bornian solvation model was applied for evaluation of the standard Gibbs energy (δGtr°,W→O) of transfer of organic ions from water (W) to organic solvent (O = nitrobenzene). The solvation energy of an ion in either W or O is basically formulated as the energy required for the formation of a nanosized ion-solvent interface around the ion; however, many organic ions with strongly charged groups (e.g., -SO3-, -CO2-, -NH3+) are preferentially hydrated in O. Here we divided the surface of an ion into hydrated and non-hydrated surfaces and then carried out regression analyses with experimental values of δGtr°,W→O. In the analyses, the local electric field on the surface of an organic ion was evaluated through density functional theory calculation. Good regression results were then obtained with the mean absolute error of 1.9 and 2.4 kJ mol-1 for 34 anions and 63 cations, respectively. These errors correspond to the error of 20 mV in the standard ion-transfer potential (δOWφ°), being only two times larger than the typical experimental error (10 mV) in the voltammetric measurement. This non-Bornian model is promising for theoretical prediction of δGtr°,W→O (or δOWφ°) for organic ions and possibly of the biomembrane permeability for ionic drugs.
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Role of 2-mercaptoethanol in direct electron transfer-type bioelectrocatalysis of fructose dehydrogenase at Au electrodes Reviewed
Yu Sugimoto, Yuki Kitazumi, Osamu Shirai, Masahiro Yamamoto, Kenji Kano
Electrochimica Acta 170 242 - 247 2015.7
Joint Work
Publisher：PERGAMON-ELSEVIER SCIENCE LTD
© 2015 Elsevier Ltd. All rights reserved. Effects of the electrode potential on a direct electron transfer (DET)-type bioelectrocatalysis of fructose dehydrogenase (FDH) at Au electrodes were investigated. Adsorbed FDH showed the highest DET activity at an adsorption potential (E<inf>ad</inf>) around the point of zero charge (E<inf>pzc</inf>). Since FDH stock solution contains 2-mercaptoethanol (ME) for stabilization, ME is partially bound to the Au electrode. However, the DET activity drastically decreased at E<inf>ad</inf> >> E<inf>pzc</inf>. Au oxide layer is formed at the positive potentials to hinder the interfacial electron transfer. In contrast, only slight decrease in the DET activity was observed at sufficiently negative E<inf>ad</inf> (<<E<inf>pzc</inf>), where ME is reductively desorbed from the Au electrode, but co-exists in the solution. In contrast, when FDH and ME were adsorbed on Au electrodes at an open circuit potential and the FDH- and ME-adsorbed Au electrode was held at such a negative hold potential (E<inf>ho</inf>) in the buffer without ME, the DET activity drastically decreased. An addition of ME in the test solution prevented the decrease in the DET activity at the negative E<inf>ho</inf>. These results indicate that ME close to adsorbed FDH plays a significant role in the stabilization of FDH adsorbed on Au electrodes.
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Yuta Otsuka, Masahiro Yamamoto, Hideji Tanaka, Makoto Otsuka
Bio-Medical Materials and Engineering 25 ( 3 ) 223 - 236 2015.6
Joint Work
Publisher：IOS Press
© 2015 - IOS Press and the authors. All rights reserved. BACKGROUND: Theophylline anhydrate (TA) in tablet formulation is transformed into monohydrate (TH) at high humidity and the phase transformation affected dissolution behavior. OBJECTIVE: Near-infrared spectroscopic (NIR) method is applied to predict the change of pharmaceutical properties of TA tablets during storage at high humidity. METHODS: The tablet formulation containing TA, lactose, crystalline cellulose and magnesium stearate was compressed at 4.8 kN. Pharmaceutical properties of TA tables were measured by NIR, X-ray diffraction analysis, dissolution test and tablet hardness. RESULTS: TA tablet was almost 100% transformed into TH after 24 hours at RH 96%. The pharmaceutical properties of TA tablets, such as tablet hardness, 20 min dissolution amount (D20) and increase of tablet weight (TW), changed with the degree of hydration. Calibration models for TW, tablet hardness and D20 to predict the pharmaceutical properties at high-humidity conditions were developed on the basis of the NIR spectra by partial least squares regression analysis. The relationships between predicted and actual measured values for TW, tablet hardness and D20 had straight lines, respectively. CONCLUSIONS: From the results of NIR-chemometrics, it was confirmed that these predicted models had high accuracy to monitor the tablet properties during storage at high humidity.
DOI： 10.3233/BME-151278
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Coextraction of water into nitrobenzene with organic ions Reviewed
Yasuhiro Naito, Wataru Murakami, Kazuo Eda, Masahiro Yamamoto, Toshiyuki Osakai
Journal of Physical Chemistry B 119 ( 19 ) 6010 - 6017 2015.5
Joint Work
© 2015 American Chemical Society. Various organic anions (sulfonates (RSO<inf>3</inf><sup>-</sup>), carboxylates (RCO<inf>2</inf><sup>-</sup>), and phenolates (RO<sup>-</sup>)) and ammonium cations (RNH<inf>3</inf><sup>+</sup>, R<inf>2</inf>NH<inf>2</inf><sup>+</sup>, and R<inf>3</inf>NH<sup>+</sup>) were distributed in the nitrobenzene (NB)-water system by using Crystal Violet and dipicrylaminate, respectively. The number of water molecules (n) being coextracted into NB with an ion was then determined by the Karl Fischer method. The n values determined and those reported previously showed the variation from 0.51 to 3.4, depending on not only the charged groups but also the noncharged R-groups. In this study, we focused our attention to the strong electric field on the charged group and its facilitation effect for binding water molecules in NB. The local electric field (E<inf>i</inf>) on the surface of an organic ion was evaluated by using Gaussian09 program with a subprogram developed in our recent study. It was found that the n values showed a clear dependence on the average value of E<inf>i</inf> on oxygen or hydrogen atoms, respectively, of an anionic or cationic group.
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A magnetic anti-cancer compound for magnet-guided delivery and magnetic resonance imaging Reviewed
Haruki Eguchi, Masanari Umemura, Reiko Kurotani, Hidenobu Fukumura, Itaru Sato, Jeong Hwan Kim, Yujiro Hoshino, Jin Lee, Naoyuki Amemiya, Motohiko Sato, Kunio Hirata, David J. Singh, Takatsugu Masuda, Masahiro Yamamoto, Tsutomu Urano, Keiichiro Yoshida, Katsumi Tanigaki, Masaki Yamamoto, Mamoru Sato, Seiichi Inoue, Ichio Aoki, Yoshihiro Ishikawa
Scientific Reports 5 2015.3
Joint Work
Research on controlled drug delivery for cancer chemotherapy has focused mainly on ways to deliver existing anti-cancer drug compounds to specified targets, e.g., by conjugating them with magnetic particles or encapsulating them in micelles. Here, we show that an iron-salen, i.e., μ-oxo N,N'- bis(salicylidene)ethylenediamine iron (Fe(Salen)), but not other metal salen derivatives, intrinsically exhibits both magnetic character and anti-cancer activity. X-Ray crystallographic analysis and first principles calculations based on the measured structure support this. It promoted apoptosis of various cancer cell lines, likely, via production of reactive oxygen species. In mouse leg tumor and tail melanoma models, Fe(Salen) delivery with magnet caused a robust decrease in tumor size, and the accumulation of Fe(Salen) was visualized by magnetic resonance imaging. Fe(Salen) is an anti-cancer compound with magnetic property, which is suitable for drug delivery and imaging. We believe such magnetic anti-cancer drugs have the potential to greatly advance cancer chemotherapy for new theranostics and drug-delivery strategies.
DOI： 10.1038/srep09194
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Electrostatic interaction between an enzyme and electrodes in the electric double layer examined in a view of direct electron transfer-type bioelectrocatalysis Reviewed
Yu Sugimoto, Yuki Kitazumi, Seiya Tsujimura, Osamu Shirai, Masahiro Yamamoto, Kenji Kano
Biosensors and Bioelectronics 63 138 - 144 2015.1
Joint Work
Publisher：ELSEVIER ADVANCED TECHNOLOGY
Effects of the electrode poential on the activity of an adsorbed enzyme has been examined by using copper efflux oxidase (CueO) as a model enzyme and by monitoring direct electron transfer (DET)-type bioelectrocatalysis of oxygen reduction. CueO adsorbed on bare Au electrodes at around the point of zero charge (Epzc) shows the highest DET activity, and the activity decreases as the adsorption potential (Ead; at which the enzyme adsorbs) is far from Epzc. We propose a model to explain the phenomena in which the electrostatic interaction between the enzyme and electrodes in the electric double layer affects the orientation and the stability of the adsorbed enzyme. The self-assembled monolayer of butanethiol on Au electrodes decreases the electric field in the outside of the inner Helmholtz plane and drastically diminishes the Ead dependence of the DET activity of CueO. When CueO is adsorbed on bare Au electrodes under open circuit potential and then is held at hold potentials (Eho) more positive than Epzc, the DET activity of the CueO rapidly decreases with the hold time. The strong electric field with positive surface charge density on the metallic electrode (σM) leads to fatal denaturation of the adsorbed CueO. Such denaturation effect is not so serious at Eho<<Epzc, but the electric field with negative σM induces an orientation inconvenient for the DET reaction during the adsorption process. A positively charged neomycin shows a promoter ability to CueO adsorbed at Ead<<Epzc. The phenomenon is also explained on the proposed model. © 2014 Elsevier B.V.
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Coextraction of Water into Nitrobenzene with Organic Ions Reviewed
Y. Naito et al.
J. Phys. Chem. B 2015
Joint Work
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Electrostatic interaction between an enzyme and electrodes in the electric double layer examined in a view of direct electron transfer-type bioelectrocatalysis Reviewed
Yu Sugimoto et al.
Biosensors and Bioelectronics 2015
Joint Work
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A magnetic anti-cancer compound for magnet-guided delivery and magnetic resonance imaging Reviewed
Yoshihiro Ishikawa et al.
Scientific Reports 2015
Joint Work
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Role of 2-mercaptoethanol in direct electron transfer-type bioelectrocatalysis of fructose dehydrogenase at Au electrodes Reviewed
Y. Sugimoto et al.
Electrochimica Acta 2015
Joint Work
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Predictive evaluation of pharmaceutical properties of direct compression tablets containing theophylline anhydrate during storage at high humidity by near-infrared spectroscopy Reviewed
Y. Otsuka et al.
Bio-Medical Materials and Engineering 2015
Joint Work
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Prediction of the Standard Gibbs Energy of Transfer of Organic Ions Across the Interface Between Two Immiscible Liquids Reviewed
Osakai, Toshiyuki et al.
J. Phys. Chem. B 2015
Joint Work
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Characteristics of fast mediated bioelectrocatalytic reaction near microelectrodes Reviewed
Yuki Kitazumi, Tatsuo Noda, Osamu Shirai, Masahiro Yamamoto, Kenji Kano
Physical Chemistry Chemical Physics 16 ( 19 ) 8905 - 8910 2014.5
Joint Work
The pseudo-steady-state current due to a mediated enzymatic reaction on a microelectrode is characterized on the basis of theoretical analysis and numerical simulation. The steady-state current is proportional to substrate concentration when the enzymatic reaction is considerably faster than substrate mass transport via nonlinear diffusion. Under such conditions, the reaction plane, where the mass flow of the substrate is converted to that of the mediator, exists near the electrode surface. The steady-state current increases as the diffusion coefficient of the substrate increases. In contrast, the diffusion coefficient and the concentration of the mediator have minor effects on the current. This difference can be explained on the basis of a change in the reaction plane location. When a sufficient amount of enzyme exists in a system, the system can be used as an amperometric biosensor, the response of which is independent of any change in enzyme activity. This journal is © the Partner Organisations 2014.
DOI： 10.1039/c4cp00141a
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Effects of the density difference between water and oil on stabilization of powdered oil-in-water emulsions Reviewed
Ryo Murakami, Hiroshi Moriyama, Tatsuyuki Noguchi, Masahiro Yamamoto, Bernard P. Binks
Langmuir 30 ( 2 ) 496 - 500 2014.1
Joint Work
A powdered oil-in-water (o/w) emulsion is a dispersed system in which the continuous phase of a particle-stabilized o/w emulsion is dispersed in air by encapsulating the water globules with hydrophobic particles. During their preparation, oil droplets in water globules are forced to move because of high-shear mixing, leading to creaming of the oil droplets and possible wetting of the hydrophobic particles with the oil droplets, which induces destabilization. To prepare powdered o/w emulsions efficiently, the extent of creaming of the oil droplets has to be suppressed. We describe how to achieve this by mixing two oils of different densities and preparing powdered o/w emulsions from oil mixtures exhibiting a decreasing density difference with water. As the extent of creaming is reduced, enhanced stabilization of the powdered emulsions occurs. © 2013 American Chemical Society.
DOI： 10.1021/la4042056
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Characteristics of fast mediated bioelectrocatalytic reaction near microelectrodes Reviewed
Y. Kitazumi et al.
Phys. Chem. Chem. Phys. 2014
Joint Work
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A Non-Bornian Analysis of the Gibbs Energy of Ion Hydration Reviewed
W. Murakami et al.
Bull. Chem. Soc. Jpn. 2014
Joint Work
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Effects of the Density Difference between Water and Oil on Stabilization of Powdered Oil-in-Water Emulsions
R .Murakami et al.
Langmuir 2014
Joint Work
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A non-Bornian analysis of the Gibbs energy of hydration for organic ions Reviewed
R. Murakami et al.
RSC. Adv. 2014
Joint Work
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A non-Bornian analysis of the Gibbs energy of hydration for organic ions
Wataru Murakami, Masahiro Yamamoto, Kazuo Eda, Toshiyuki Osakai
RSC Advances 4 ( 53 ) 27634 - 27641 2014
Joint Work
Recently, a non-Bornian model was successfully applied to evaluate the Gibbs energy of hydration (ΔG°hyd) for spherical ions (mainly inorganic ions). In this model, the long-range, Born-type electrostatic ion-solvent interaction is not explicitly included in the calculation of ΔG°hyd, since its contribution is small, whereas the short-range interaction, including Coulomb, polarization, and charge-transfer interactions, is considered as the dominant factor that determines the ΔG°hyd of ions. The ΔG°hyd scaled by the surface area of an ion can be given by a quadratic function of the surface field strength (E) of the ion. In this study, the non-Bornian model was further applied to organic ions with charged groups. Using the Gaussian 09 program package, the geometries of ions in vacuum were optimized at the B3LYP/6-311++G(2d,p) level, and the partial atomic charges were computed in the Mulliken, Merz-Kollman (MK), natural population analysis (NPA), Hirshfeld, and ChelpG methods. Introducing a new subprogram, we could estimate local electric fields on the ion surface (van der Waals surface or solvent-accessible surface (SAS)). This enabled us to perform regression analyses based on the non-Bornian model, by using the experimental values of ΔG°hyd for 109 ions. When the NPA-SAS combination was chosen, the best regression result was obtained, giving the mean absolute error of 4.3 kcal mol-1. The non-Bornian model would provide a simple and relatively accurate way of determining ΔG°hyd of ions. This journal is © the Partner Organisations 2014.
DOI： 10.1039/c4ra02422b
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A non-bornian analysis of the gibbs energy of ion hydration
Wataru Murakami, Kazuo Eda, Masahiro Yamamoto, Toshiyuki Osakai
Bulletin of the Chemical Society of Japan 87 ( 3 ) 403 - 411 2014
Joint Work
A non-Bornian model for understanding the Gibbs energy of ion hydration (δG°hyd) has been proposed, in which only short-range interactions between an ion and solvent molecules adjacent to the ion are considered, while the longrange electrostatic interaction between the ion and the outer bulk solvent is not explicitly included in the model. As the short-range interactions, Coulomb, polarization, and charge-transfer interactions are taken into account. It has thus been shown that the δG°hyd scaled by the solvent-accessible surface (SAS) area of an ion can be given by a quadratic function of the electric field strength E at the SAS. Regression analyses with the derived analytical equation have been performed for the literature values of δG°hyd for spherical ions, including 85 cations (with the charge number, z = 1 to 4) and 53 anions (with z = 1 and 2); good fitting results have been obtained for either the cations or the anions. An additional regression analysis has been performed for 10 representative cations, using the data set employed by Koehl et al. (J. Phys. Chem. B 2009, 113, 5694). Our non-Bornian model has been found to be one of the highest performance models for the prediction of δG°hyd. © 2013 The Chemical Society of Japan.
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A revisit to the non-Bornian theory of the Gibbs energy of ion transfer between two immiscible liquids Reviewed
Wataru Murakami, Kazuo Eda, Masahiro Yamamoto, Toshiyuki Osakai
Journal of Electroanalytical Chemistry 704 38 - 43 2013.9
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Potentiometric coulometry based on charge accumulation with a peroxidase/osmium polymer-immobilized electrode for sensitive determination of hydrogen peroxide Reviewed
Chi-Hua Nieh, Yuki Kitazumi, Osamu Shirai, Masahiro Yamamoto, Kenji Kano
Electrochemistry Communications 33 135 - 137 2013.8
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Effects of polymorphic transformation on pharmaceutical properties of direct compressed tablets containing theophylline anhydrate bulk powder under high humidity Reviewed
Yuta Otsuka, Masahiro Yamamoto, Hiroyuki Abe, Makoto Otsuka
Colloids and Surfaces B: Biointerfaces 102 931 - 936 2013.2
Joint Work
The effect of high humidity on the pharmaceutical properties of direct compression tablets containing theophylline anhydrate (TA) was investigated to prepare high quality pharmaceuticals. A mixed powder (230. mg) containing the TA, β-lactose anhydrate, microcrystalline cellulose (MCC) and magnesium stearate was compressed in a die by 8-mm diameter punches with flat surfaces at 4.8. kN. The TA tablets were stored in desiccators at 96% relative humidity and 20°C. Physicochemical properties of the tablets were measured using, powder X-ray diffraction (XRD), X-ray computed tomography (XCT), the tablet hardness test and the dissolution test. The water absorption process could be divided into two stages: 1.0% absorption at for 0-6. h due to absorption of MCC, and 4% absorption at 6-24. h due to hydration of TA. The XRD and XCT results were supported be tablet weight changes in the initial and later stages, respectively. The relationship between tablet hardness and water absorption indicated that the first stage of absorption was more significant. In contrast, the relationship between the dissolved amount at 20. min (D20) and water absorption indicated that the first stage was less effective. The first stage of absorption was due to MCC, but the second was due to hydration of the TA bulk powder. © 2012 Elsevier B.V.
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Numerical simulation of diffuse double layer around microporous electrodes based on the Poisson-Boltzmann equation Reviewed
Y. Kitazumi et al.
Electrochimica Acta 2013
Joint Work
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Effects of polymorphic transformation on pharmaceutical properties of direct compressed tablets containing theophylline anhydrate bulk powder under high humidity Reviewed
Y. Otsuka et al.
Colloids and Surfaces B: Biointerfaces 2013
Joint Work
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Diffusion-controlled Detection of Glucose with Microelectrodes in Mediated Bioelectrocatalytic Oxidation Reviewed
T. Noda et al.
Anal. Sci. 2013
Joint Work
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Potentiometric coulometry based on charge accumulation with a peroxidase/osmium polymer-immobilized electrode for sensitive determination of hydrogen peroxide Reviewed
Chi-Hua Nieh et al.
Electrochem. Comm. 2013
Joint Work
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A revisit to the non-Bornian theory of the Gibbs energy of ion transfer between two immiscible liquids Reviewed
T. Osakai et al.
J. Electroanal. Chem. 2013
Joint Work
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Tatsuo NODA, Mizue WANIBUCHI, Yuki KITAZUMI, Seiya TSUJIMURA, Osamu SHIRAI, Masahiro YAMAMOTO, Kenji KANO
Analytical Sciences 29 ( 3 ) 279 - 281 2013
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Numerical simulation of diffuse double layer around microporous electrodes based on the Poisson-Boltzmann equation
Yuki Kitazumi, Osamu Shirai, Masahiro Yamamoto, Kenji Kano
Electrochimica Acta 112 171 - 175 2013
Joint Work
The structure of the diffuse double layer around a nm-sized micropore on porous electrodes has been studied by numerical simulation using the Poisson-Boltzmann equation. The double layer capacitance of the microporous electrode strongly depends on the electrode potential, the electrolyte concentration, and the size of the micropore. The potential and the electrolyte concentration dependence of the capacitance is different from that of the planner electrode based on the Gouy's theory. The overlapping of the diffuse double layer becomes conspicuous in the micropore. The overlapped diffuse double layer provides the mild electric field. The intensified electric field exists at the rim of the orifice of the micropore because of the expansion of the diffuse double layers. The characteristic features of microporous electrodes are caused by the heterogeneity of the electric field around the micropores. © 2013 Elsevier Ltd. All rights reserved.
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Particle Stabilization of Oil-in-Water-in-Air Materials: Powdered Emulsions Reviewed
Ryo Murakami, Hiroshi Moriyama, Masahiro Yamamoto, Bernard P. Binks, Anaïs Rocher
Advanced Materials 24 ( 6 ) 767 - 771 2012.2
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“Particle stabi- lization of oil-in-water-in-air materials: powdered emulsions” Reviewed
Murakami, R.; Moriyama, H.; Yamamoto, M.; Binks, B. P.; Rocher, A.
Advanced Materials 24 767 - 771 2012
Joint Work
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Yamamoto Masahiro
Review of Polarography 58 ( 2 ) 103 - 104 2012
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“Phase-Separation of Ordered D03 Precipitates in A2 + D03 Two-Phase Microstructure of Fe-Si-V Ternary Alloy System ” Reviewed
K. Ota, T. Shinoda, T. Hayashi, T. Kozakai, M. Doi, M. Yamamoto, M. Takagi, A. Matsumuro,
Processing and Fabrication of Advanced Materials XVIII 18 12 - 14 2009
Joint Work
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Lattice widening in niobium-doped TiO<inf>2</inf> nanotubes: Efficient ion intercalation and swift electrochromic contrast Reviewed
Andrei Ghicov, Masahiro Yamamoto, Patrik Schmuki
Angewandte Chemie - International Edition 47 ( 41 ) 7934 - 7937 2008.9
Joint Work
Widely accommodating: Novel TiO2/Nb nanotube layers (see picture, right) are grown on a titanium-niobium alloy. Niobium doping of TiO2 enlarges the cell parameters of the anatase lattice (left; Nb green, Ti gray, O red), facilitating the intercalation of H+ and Li+ ions, and even larger Na+ ions (blue) into the lattice. (Figure Presented) © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
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Artificially phase-separated binary self-assembled monolayers composed of 11-amino-1-undecanethiolate and 10-carboxy-1-decanethiolate on Au(1 1 1): A comparative study of two preparing methods Reviewed
Pham Hong Phong, Hyroyuki Tomono, Naoya Nishi, Masahiro Yamamoto, Takashi Kakiuchi
Electrochimica Acta 53 ( 14 ) 4900 - 4906 2008.5
Joint Work
Publisher：PERGAMON-ELSEVIER SCIENCE LTD
Two methods have been compared for preparing artificially phase-separated two-component SAMs on Au(1 1 1) composed of 11-amino-1-undecanethiolates (AUTe) and 10-carboxyl-1-decanethiolates (CDTe), which would form, thermodynamically, a homogeneously mixed binary SAMs. The first method starts with the formation of a phase-separated binary SAM of AUTe and 2-hydroxy-1-ethanethiolate (HETe) as a template of the artificially phase-separated SAM, followed by the selective desorption of HETe domains and succeeding filling of the vacancy with CDTe. The second method utilizes fluoren-9-ylmethyl N-(11-mercaptoundecyl) carbamate (FMUCe) instead of 11-amino-1-undecanethiol in preparing the template. After the filling with CDTe, the 9-fluorenylmethyloxycarbonyl (Fmoc) group is removed to obtain AUTe domains. Both methods yield artificially phase-separated binary SAMs having AUTe domains of tens nanometer across. The molecularly flat SAM surface with nanometer-scale domains of different acid-base and electrostatic properties are thus created. For preparing binary SAMs with a higher degree of phase separation, the second method is a better choice; a more clear-cut phase separation is achieved. © 2008 Elsevier Ltd. All rights reserved.
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Counterion binding induces attractive interactions between negatively-charged self-assembled monolayer of 3-mercaptopropionic acid on Au(111) in reductive desorption Reviewed
Yukio Kitagawa, Daisuke Hobara, Masahiro Yamamoto, Takashi Kakiuchi
Journal of Solid State Electrochemistry 12 ( 4 ) 461 - 469 2008.4
Joint Work
Publisher：SPRINGER
The electrochemical reductive desorption of the self-assembled monolayers of 3-mercaptopropionic acid in an aqueous alkaline solution gives a sharp peak with the full width at half maximum of about 20 mV irrespective of the type of cations in a linear scan voltammogram. This suggests that a strong attractive interaction exists between negatively charged carboxylate groups in the self-assembled monolayer surface due to the counterion binding, which not only simply stabilizes the adsorbed carboxylates but also makes the interaction between the adsorbed thiolates even attractive possibly by forming a two-dimensional ionic crystal. The effect of tetraalkylammonium ions on the shape of the voltammograms was also examined. © 2007 Springer-Verlag.
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``Lattice Widening in Niobium-Doped TiO2 Nanotubes: Efficient Ion Intercalation and Swift Electrochromic Contrast," Reviewed
Ghicov, A.; Yamamoto, M.; Schumki, P.
Angew. Chem. Int. Ed., 47 1 - 5 2008
Joint Work
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``Artificially phase-separated binary self-assembled monolayers composed of 11-amino-1-undecanethiolate and 10-carboxy-1-decanethiolate on Au(111): A comparative study of two preparing methods," Reviewed
Phong, P. H.; , Tomono ,H.; Nishi, N.; Yamamoto, M. and Kakiuchi, T.
Electrochimica Acta 53 4900 - 4906 2008
Joint Work
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``Counterion Binding Induces Attractive Interaction between Negatively-charged Self-assembled Monolayer of 3-Mercaptopropionic Acid on Au(111) in Reductive Desorption," Reviewed
Kitagawa, Y.; Hobara, D.; Yamamoto, M.; Kakiuchi, T.
J. Solid State Electrochem. 12 461 - 469 2008
Joint Work
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Orientation of 1-dodecyl-4-phenylpyridinium ions constituting an ionic liquid at the ionic liquid | water interface studied by second harmonic generation Reviewed
Naoya Nishi, Ryoichi Ishimatsu, Masahiro Yamamoto, Takashi Kakiuchi
Journal of Physical Chemistry C 111 ( 33 ) 12461 - 12466 2007.8
Joint Work
A hydrophobic room-temperature ionic liquid (RTIL) of 1-dodecyl-4- phenylpyridinium (C12ppy+) ions, the cations with high first hyperpolarizability, was prepared in combination with bis(pentafluoroethylsulfonyl)imide, and the orientation of C 12ppy+ at the RTIL|water and RTIL|air interfaces was analyzed using optical second harmonic generation (SHG). From polarization-dependence measurements and absolute phase measurements, it was found that C12ppy+ ions at the RTIL|air interface are orientated with the main axis of 4-phenylpyridinium moiety (from phenyl to pyridinium direction) tilted at 53° from the surface normal (from RTIL to air direction) and that the dodecyl chain is protruding to the air. At the RTIL|water interface, it was suggested that C12ppy+ is orientated at the tilt angle of 131° from the surface normal (from RTIL to water direction) with the dodecyl chain protruding away from the aqueous phase. © 2007 American Chemical Society.
DOI： 10.1021/jp071538v
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Concentration-dependent switching of the mode of phase separation in ternary self-assembled monolayers of 2-mercaptoethane sulfonic acid, 2-aminoethanethiol and 1-dodecanethiol on Au(111) Reviewed
Pham Hong Phong, Vladimir V. Sokolov, Naoya Nishi, Masahiro Yamamoto, Takashi Kakiuchi
JOURNAL OF ELECTROANALYTICAL CHEMISTRY 600 ( 1 ) 35 - 44 2007.2
Joint Work
Publisher：ELSEVIER SCIENCE SA
Unusually strong apparent surface activity of the pair of 2-mercaptoethane sulfonic acid (MES) and 2-aminoethanethiol (AET) in forming a phase-separated ternary self-assembled monolayer (SAM) composed of MES, AET, and 1-dodecanethiol (DDeT) has been investigated with changing the conditions for preparing the SAM by coadsorption of the thiols from an ethanolic solution. When the total concentration of the thiols, c(total), is 1 x 10(-3) mol dm(-3) or higher, the MES-AET pair forms electrostatically stabilized domains from an early stage of the adsorption after the immersion of a gold substrate in the bathing ethanol solution. The total area of the MES-AET domains does not change with time for longer immersion. The adsorption of DDeT is significantly weaker than the MES-AET pair under such conditions, despite the fact that the intrinsic surface activity of DDeT is greater than those of MES and AET. DDeT-rich islands of typically a few nanometer across spread in the SAM and the size and the distribution of the islands are invariant over a week. In contrast, when c(total) is lower than 0.1 x 10(-3) mol dm(-3), the adsorptivity of DDeT is stronger than that of the MES-AET pair, and MES and AET initially adsorbed are gradually replaced with DDeT at longer immersion time. This switching of the mode of phase separation with the change in c(total) suggests the crucial roles of the electrostatic interaction of MES and AET in the course of the formation of the SAM and of the hydrophilic barrier formed on the domains to prevent the replacement by hydrophobic DDeT molecules. (c) 2006 Elsevier B.V. All rights reserved.
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“Concentration- dependent Switching of the Mode of Phase Separation in Ternary Self-assembled Monolayers of 2-Mercaptoethane Sulfonic acid, 2-Aminoethanethiol and 1-Dodecanethiol on Au(111),” Reviewed
Phong, P. H.; Sokolov, V. V.; Nishi, N.; Yamamoto, M.; Kakiuchi, T.
J. Electroanal. Chem. 600 35 - 44 2007
Joint Work
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“Orientation of 1-dodecyl-4-phenylpyridinium ions constituting an ionic liquid at the ionic liquid—water interface studied by second harmonic generation,” Reviewed
Nishi, N.; Yamamoto, M.; Kakiuchi, T.
J. Phys. Chem. C 111 12461 - 12466 2007
Joint Work
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“光第二高調波発生法による N-アルキルイソキノリ ニウム系イオン液体 | 水界面の構造解析,” Reviewed
西直哉, 山本雅博,垣内隆
分析化学 56 491 - 497 2007
Joint Work
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Optical second harmonic generation study of the structure of the interface between water and an ionic liquid based on N-alkylisoquinolinium ions Reviewed
Naoya Nishi, Masahiro Yamamoto, Takashi Kakiuchi
Bunseki Kagaku 56 ( 6 ) 491 - 497 2007
Joint Work
The orientation of cations at the interface between water and a room-temperature ionic liquid (RTIL) has been analyzed using optical second harmonic generation. To detect second harmonic light from the RTIL|water interface with high sensitivity, a RTIL, N-dodecylisoquinolinium bis(pentafluoroethylsulfonyl)imide, which is based on N-dodecylisoquinolinium (C12Iq+) having strong hydrophobicity and high hyperpolarizability, has been used. A polarization-dependence measurement of the light intensity of the second harmonic light has suggested that C 12Iq+ is orientated at the RTIL|water interface with the isoquinolinium moiety tilting at 50° with respect to the surface normal, and with the dodecyl moiety protruding to the RTIL phase. © 2007 The Japan Society for Analytical Chemistry.
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Dependence of the redox reaction of cytochrome c on the mixing state of binary self-assembled monolayers composed of 11-aminoundecanethiol and 10-mercaptoundecanoic acid on Au(1 1 1) Reviewed
Pham Hong Phong, Masahiro Yamamoto, Takashi Kakiuchi
Science and Technology of Advanced Materials 7 ( 6 ) 552 - 557 2006.9
Joint Work
Electron transfer (ET) of horse heart cytochrome c (cyt c) immobilized on the artificially phase-separated binary self-assembled monolayers (SAMs) composed of 11-amino-1-undecanthiolate (AUTe) and 10-carboxy-1-decanethiolate (MUAe), (p-SAMs) has been investigated. It has been found that cyt c selectively adsorbs on domains of MUAe of the p-SAMs by the electrostatic attraction and the ET of cyt c on p-SAMs is enhanced compared to that of cyt c adsorbed on the homogeneously mixed SAM of AUTe and MUAe and also on the single-component MUA SAM. This suggests a favorable orientation of cyt c on p-SAMs for ET with the electrode. © 2006 NIMS and Elsevier Ltd.
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Fluorine-free and hydrophobic room-temperature ionic liquids, tetraalkylammonium bis(2-ethylhexyl)sulfosuccinates, and their ionic liquid–water two-phase properties Reviewed
Naoya Nishi, Takahiro Kawakami, Fumiko Shigematsu, Masahiro Yamamoto, Takashi Kakiuchi
Green Chemistry 8 ( 4 ) 349 - 355 2006.3
Joint Work
Fluorine-free and hydrophobic room-temperature ionic liquids (RTILs) composed of the bis(2-ethylhexyl)sulfosuccinate (BEHSS) ion, which is known as the surface-active anion constituting Aerosol OT®, and symmetric tetraalkylammonium ions ((CnH2n+1)4N+; n = 4–8), have been prepared. Physicochemical properties of the water-saturated RTILs such as density, conductivity, viscosity and mutual solubility with water (W) have been measured. The RTIL|W interface is polarizable for the RTILs with n = 5–8 in spite of the high water content, 3.6–8.9 wt% in the water-saturated RTILs. The width of the polarized potential window of the RTIL|W interfaces is quantitatively correlated with the solubility of the RTIL in W. The RTIL–W two-phase systems are not spontaneously emulsified and no reverse micelles are formed in the water-saturated RTILs, although BEHSS- is known to form stable water-in-oil emulsions and reverse micelles in oil–water two-phase systems. © 2006 The Royal Society of Chemistry.
DOI： 10.1039/b511529a
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“Dependence of the redox reaction of cy- tochrome c on the mixing state of binary self-assembled monolayers composed of 11-aminoundecanethiol and 10-mercaptoundecanoic acid on Au(111)” Reviewed
Phong, P.H.; Yamamoto, M.; Kakiuchi, T.
Science and Technology of Advanced Materials 7 552 - 557 2006
Joint Work
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Novel hydrophobic molten salts based on tetrakis[3,5-bis(trifluoromethyl) phenyl]borate anion for electrochemistry of the molten salt|water interface
Seiichi Imakura, Naoya Nishi, Masahiro Yamamoto, Takashi Kakiuchi
Proceedings - Electrochemical Society PV 2004-24 523 - 527 2006
Joint Work
The polarized potential window at the room-temperature molten salt (RTMS)|water (W) interface can be widened using RTMSs composed of a hydrophobic anion, tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB). The cations which we used for TFPB-based salts are 1-alkyl-3-methylimidazolium (C nmim+: n = 2,4-8,10,12), N-dodecylpyridinium (C nPy+), trioctylmethylammonium (TOMA+), and N-alkylisoquinolinium (CnIq+, n = 12, 18). Among the RTMSs investigated, [C18Iq][TFPB] is in the liquid state at room temperature. The width of the potential window of [C18Iq][TFPB]|W interface is 800 mV, which allows us to study the transfer of moderately hydrophilic cations and moderately hydrophobic anions across the interface.
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Physicochemical properties of room-temperature molten salts of symmetrical tetraalkyl ammonium diisooctylsulfosuccinates
Takahiro Kawakami, Fumiko Shigematsu, Naoya Nishi, Masahiro Yamamoto, Takashi Kakiuchi
Proceedings - Electrochemical Society PV 2004-24 519 - 522 2006
Joint Work
Novel fluorine-free and water-immiscible room-temperature molten salts (RTMSs) composed of symmetrical tetraalkylammonium (Nnnnn· n: length of alkyl chain, n = 4-8) and diisooctylsulfosuccinate (DOSS) have been synthesized. Density, conductivity, and water content of the water-saturated RTMSs at 25°C have been measured. Cyclic voltammograms at the N nnnnDOSS|water interfaces show that the interfaces are polarizable and the width of the potential window at the N6666DOSS |water interface is ca. 300 mV.
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Ideal nonideality in adsorption of 2-aminoethanethiol and 2-mercaptoethane sulfonic acid to form electrostatically stabilized binary self-assembled monolayers on Au(111) Reviewed
Yosuke Ooi, Daisuke Hobara, Masahiro Yamamoto, Takashi Kakiuchi
Langmuir 21 ( 24 ) 11185 - 11189 2005.11
Joint Work
In formation of binary self-assembled monolayers (SAMs) composed of 2-aminoethanethiol (AET) and 2-mercaptoethane sulfonic acid (MES) by adsorption from an ethanol solution on Au(111), the adsorption shows nearly ideal nonideality in that the surface ratio of MES to AET in the SAM is unity and does not depend on the mixing ratio of MES to AET in the bathing ethanol solution used for preparing SAMs, χMESsoln, over the wide range of χMESsoln between 0.01 and 0.95. X-ray photoelectron spectroscopy confirms that at least 80% of AET molecules adsorbed are protonated in this range of χMESsoln, indicating that the electrostatic interaction between positively charged AET and negatively charged MES is responsible to the observed nonideality. Correspondingly, there appears only one cathodic peak in a linear-sweep voltammogram of the reductive desorption of the SAM, having a narrow full width at half-maximum of about 20 mV. This suggests the presence of strong lateral attractive interaction between the adsorbed thiolates. © 2005 American Chemical Society.
DOI： 10.1021/la051160x
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Phase separation of ternary self-assembled monolayers into hydrophobic 1-dodecanethiol domains and electrostatically stabilized hydrophilic domains composed of 2-aminoethanethiol and 2-mercaptoethanesulfonic acid on Au(111) Reviewed
Pham Hong Phong, Yosuke Ooi, Daisuke Hobara, Naoya Nishi, Masahiro Yamamoto, Takashi Kakiuchi
Langmuir 21 ( 23 ) 10581 - 10586 2005.11
Joint Work
Ternary self-assembled monolayers (SAM) composed of 2-aminoethanethiol (AET), 2-mercaptoethane-sulfonic acid (MES), and 1-dodecanethiol (DDeT) form two types of domains as if it were a two-component SAM: DDeT-rich hydrophobic domains and electrostatically stabilized hydrophilic domains composed of MES and AET on Au(111). MES and AET behave virtually as a single surface-active species. Two distinct reductive desorption peaks in cyclic voltammograms (CV) and binarized images of scanning tunneling microscopy clearly show nanometer scale, yet macroscopically distinguishable, phase separation over a wide range of the mixing ratio of DDeT and MES-AET in the bathing solution. X-ray photoelectron spectroscopy measurements indicate that the ratio of MES to AET in the hydrophilic domains is unity and that both terminal groups are in the charged states, that is, the sulfonate group and the ammonium group. With decreasing the total concentration of the thiols, the mole fraction of DDeT in the bathing solution at which the surface coverage of MES-AET domains is equal to that of DDeT domains dramatically decreases. This suggests that the adsorption kinetics plays a crucial role in the formation of the domains structure. © 2005 American Chemical Society.
DOI： 10.1021/la050444e
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Effect of the charged state of gold substrates on the surface composition of two-component alkanethiol self-assembled monolayers Reviewed
Takeo Arakawa, Daisuke Hobara, Masahiro Yamamoto, Takashi Kakiuchi
Electrochemistry Communications 7 ( 8 ) 848 - 852 2005.8
Joint Work
The surface composition of the binary self-assembled monolayer (SAM) of 1-tetradecanethiol and 3-mercapto-1-propanol on gold varies with the charged state of the gold substrate because of the difference in the reductive desorption potentials of the two thiol species. This is a direct corollary of the finding by Paik et al. [S. Eu, W.K. Paik, Chem. Lett. 16 (1998) 405-406.] that the adsorption of thiols to a metal surface from the solution phase leads to the accumulation of negative charges on the surface. By controlling the potential of the gold substrate during the formation of a binary SAM, it is possible to change the surface composition. The saturation of the bathing ethanol solution with oxygen and the grounding of the substrate during the formation of the SAM have basically the same effect on the surface composition, as both mitigate the charge-up problem. © 2005 Elsevier B.V. All rights reserved.
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Fluorescence lifetime measurements of coumarin 343 for sub-ps solvation dynamics in W|aerosol-OT|1,2-dichloroethane reverse micelle systems Reviewed
Yasunobu Iwami, Masahiro Yamamoto, Naoya Nishi, Takashi Kakiuchi
Bunseki Kagaku 54 ( 6 ) 485 - 494 2005.6
Joint Work
The sub-ps solvation dynamics in a water|Aerosol OT (AOT)|1,2- dichloroethane (DCE) reverse micelle system has been investigated by fluorescence lifetime measurements of coumarin 343. From absorption spectroscopic measurements, the fluorescence dye molecules were found to be located at the outer side of the reverse micelle interface. The diffusive part of the sub-ps solvation became slower for smaller micelles with the radius of 2-4 nm. This may be due to the interaction between water and AOT molecules in the smaller micelles. © 2005 The Japan Society for Analytical Chemistry.
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Changes in electronic structure upon lithium insertion into the a-site deficient perovskite type oxides (Li,La)TiO<inf>3</inf> Reviewed
Masanobu Nakayama, Tatsuya Usui, Yoshiharu Uchimoto, Masataka Wakihara, Masahiro Yamamoto
Journal of Physical Chemistry B 109 ( 9 ) 4135 - 4143 2005.3
Joint Work
Investigation on variation of the electronic structure accompanying the electrochemical lithium insertion into the perovskite type oxide, (Li,La)TiO3, has been carried out by X-ray absorption spectroscopy (XAS). During the electrochemical lithium insertion, titanium ion reduced its oxidation state from Ti4+ to Ti3+, while La3+ does not contribute to the reduction reaction resulting from Ti K-edge and La L3-edge XAS, respectively. Furthermore, O K-edge XAS showed marked spectral changes with electrochemical lithium insertion, indicating the electronic structure around oxide ion affected by lithium insertion reaction. From the XAS measurement, we have concluded the variation observed in O K-edge XAS was related to the strong interaction with inserted Li ion. To confirm this, first-principles band calculations were performed for the perovskite structure before and after electrochemical lithium insertion. The calculated results showed that the electron originated from inserted Li transferred to neighboring oxide ion locally as well as to Ti ion. This may be due to local neutralization effect of Li to reduce the electrostatic interaction in the crystal. © 2005 American Chemical Society.
DOI： 10.1021/jp046062j
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Polarized potential window available at the interface between an aqueous electrolyte solution and tetraalkylammonium imide salts Reviewed
Takashi Kakiuchi, Norihiro Tsujioka, Kenji Sueishi, Naoya Nishi, Masahiro Yamamoto
Electrochemistry 72 ( 12 ) 833 - 835 2004.12
Joint Work
The polarized potential window (ppw) of 450 mV is available at the interface between water (W) and the room-temperature molten salt (RTMS) that consists of tetraoctylammonium cations and trifluoromethylsulfonylnonafluorobulylsulfonylimide anions. The ppw at the interface between W and RTMS made of several combinations of hydrophobic cations and anions is correlated with the standard ion-transfer potentials of the ions at the 1,2-dichloroethane |W interface. This correlation is useful not only to predict the width of the ppw but also to approximately estimate the point of zero charge at the RTMS|W interface.
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Electrocapillarity at the nonpolarized interface between the aqueous solution and the room-temperature molten salt composed of 1-octyl-3- methylimidazolium bis(pentafluoroethylsulfonyl)imide Reviewed
Takashi Kakiuchi, Fumiko Shigematsu, Takuya Kasahara, Naoya Nishi, Masahiro Yamamoto
Physical Chemistry Chemical Physics 6 ( 18 ) 4445 - 4449 2004.9
Joint Work
The interfacial tension between the room-temperature molten salt (RTMS, also called ionic liquid) composed of 1-octyl-3-methylimidazolium bis(perfluoroethylsulfonyl)imide (C8mimC2C2N) and the aqueous solution containing 1-octyl-3-methylimidazolium chloride or lithium bis(perfluoroethylsulfonyl)imide has been measured as a function of the composition of the aqueous phase. The phase-boundary potential calculated for this non-polarized interface from the solution composition enables us to construct the corresponding electrocapillary curve, which shows a parabolic shape with respect to the variation of the phase-boundary potential over 300 mV. C8 mim+ ions specifically adsorb at the interface. Switching of the potential-determining ion from C8mim+ to C2C2N- causes a jump of more than 160 mV in the potential at the outer Helmholtz plane on the aqueous side of the interface.
DOI： 10.1039/b408333b
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Determination of the potential of zero charge of Au(1 1 1) electrodes modified with thiol self-assembled monolayers using a potential-controlled sessile drop method Reviewed
Yasunobu Iwami, Daisuke Hobara, Masahiro Yamamoto, Takashi Kakiuchi
Journal of Electroanalytical Chemistry 564 ( 1-2 ) 77 - 83 2004.3
Joint Work
The potential of zero charge (pzc) of the thiol-modified Au(111) electrode has been determined for self-assembled monolayers (SAMs) of octadecanethiolate (ODT), undecanethiolate (UDT), propanethiolate (PT), and 1H,1H,2H,2H-perfluorodecanethiolate (PFDT) by measuring the contact angle of a drop of an aqueous 0.1 moldm-3 NaClO4 solution on the SAM-covered electrode as a function of the electrode potential. The values of the pzc for ODT, UDT, PT, and PFDT SAMs were -0.52, -0.49. -0.3, and 1.04 V (vs. Ag|AgCl|satd. KCl), respectively. The variation of the values is ascribed to the change in the surface potential on the solution side of the electrode|solution interface due to the difference in the dipole moments of alkanethiolates on Au(111), which is supported by the ab initio calculation of these thiolates adsorbed on a four-atom cluster of Au atoms. © 2003 Elsevier B.V. All rights reserved.
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Electrochemical instability in the transfer of cationic surfactant across the 1,2-dichloroethane/water interface Reviewed
Takuya Kasahara, Naoya Nishi, Masahiro Yamamoto, Takashi Kakiuchi
Langmuir 20 ( 3 ) 875 - 881 2004.2
Joint Work
The electrochemical instability has been shown to appear in the transfer of cationic surfactant ions across the 1,2-dichloroethane/water interface. Cyclic voltammograms possess all fundamental characteristics that are predicted by the theory of electrochemical instability: the presence of the instability window, that is, the potential range where the interface becomes unstable, the location of the instability window around the standard ion transfer potential of surface-active ions, and the dependence of the width of the instability window on the concentration of the surfactant ions. Electrocapillary measurements clearly demonstrate that the interface becomes unstable, while the interfacial tension is positive, being higher than 20 mN m-1. The electrocapillary curve exhibits the discontinuities at both ends of the instability window, indicating the similarity between the electrochemical instability and the phase transitions induced by the temperature, pressure, and chemical potential. The results from voltammetry and interfacial tension measurements for cationic surfactants support the idea that the electrochemical instability, so far reported in the transfer of anionic surfactants across the liquid/liquid interface, is one of intrinsic properties of the two-phase systems where the partition of surface-active ions takes place.
DOI： 10.1021/la035452e
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Morihiro Saito, Hiromasa Ikuta, Yoshiharu Uchimoto, Masataka Wakihara, Shoichi Yokoyama, Takeshi Yabe, Masahiro Yamamoto
The Journal of Physical Chemistry B 107 ( 42 ) 11608 - 11614 2003.10
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Naoya Nishi, Daisuke Hobara, Masahiro Yamamoto, Takashi Kakiuchi
Langmuir 19 ( 15 ) 6187 - 6192 2003.7
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Influence of Lewis acidic borate ester groups on lithium ionic conduction in polymer electrolytes Reviewed
Yuki Kato, Kentaro Suwa, Hiromasa Ikuta, Yoshiharu Uchimoto, Masataka Wakihara, Shoichi Yokoyama, Takeshi Yabe, Masahiro Yamamoto
Journal of Materials Chemistry 13 ( 2 ) 280 - 285 2003.2
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Naoya Nishi, Daisuke Hobara, Masahiro Yamamoto, Takashi Kakiuchi
The Journal of Chemical Physics 118 ( 4 ) 1904 - 1911 2003.1
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Total-internal-reflection Broad-bandwidth Sum Frequency Generation Spectroscopy of Hexadecanethiol Adsorbed on Thin Gold Film Deposited on CaF2 Reviewed
Naoya NISHI, Daisuke HOBARA, Masahiro YAMAMOTO, Takashi KAKIUCHI
Analytical Sciences 19 ( 6 ) 887 - 890 2003
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Morihiro Saito, Hiromasa Ikuta, Yoshiharu Uchimoto, Masataka Wakihara, Shoichi Yokoyama, Takeshi Yabe, Masahiro Yamamoto
Journal of The Electrochemical Society 150 ( 4 ) A477 - A477 2003
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Takashi Kakiuchi, Hideyuki Usui, Daisuke Hobara, Masahiro Yamamoto
Langmuir 18 ( 13 ) 5231 - 5238 2002.6
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Naoya Nishi, Kazuo Izawa, Masahiro Yamamoto, Takashi Kakiuchi
The Journal of Physical Chemistry B 105 ( 34 ) 8162 - 8169 2001.8
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Reconstruction of Au(111) Following the Reductive Desorption of Self-Assembled Monolayers of 2-Mercaptoethanesulfonic Acid Studied by in Situ Scanning Tunneling Microscopy Reviewed
Daisuke Hobara, Masahiro Yamamoto, Takashi Kakiuchi
Chemistry Letters 30 ( 4 ) 374 - 375 2001.4
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Molecular Dynamics Simulation of the Transfer of a small and a Large Ion Across the NitrobenzenejWater Interface Reviewed
Yamamoto, M, Kakiuchi
Anal. Sci. 17 i239 - i240 2001
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Structure of the Pt(111)/liquid interface: a first-principles/RHNC calculation Reviewed
Masahiro Yamamoto, Masahiro Kinoshita, Takashi Kakiuchi
Electrochimica Acta 46 ( 2-3 ) 165 - 174 2000.11
Joint Work
Authorship：Lead author, Corresponding author Publisher：Elsevier BV
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Daisuke HOBARA, Kazuhiro UEDA, Shin-ichiro IMABAYASHI, Masahiro YAMAMOTO, Takashi KAKIUCHI
Electrochemistry 67 ( 12 ) 1218 - 1220 1999.12
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Position-dependent stopping power of low velocity rare gas atoms at a SnTe(0 0 1) surface Reviewed
Kaoru Nakajima, Yukihiro Fukusumi, Kenji Kimura, Michi-Hiko Mannami, M. Yamamoto, S. Naito
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms 149 ( 1-2 ) 31 - 37 1999.1
Publisher：Elsevier
Energy losses of 15-30 keV Ne+, Ar+ and Kr+ ions specularly reflected from a SnTe(001) surface are measured. Because more than 98% of the reflected ions are neutral, the observed energy loss can be considered as the result of atom-surface interactions. From the observed energy losses, position-dependent stopping powers of the SnTe(001) surface for neutral atoms are derived. The obtained stopping powers are compared with the theory of the stopping power for low velocity ions with help of the local density approximation. While the agreement between the experimental and theoretical results is excellent for Ar and Kr atoms, the experimental stopping is about twice larger than the theoretical one for Ne atoms. This discrepancy can be explained in terms of the effect of excited atoms on the stopping power. © 1999 Elsevier Science B.V.
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Position-dependent stopping power of low velocity rare gas atoms at a SnTe(001) surface Reviewed
Nucl. Instr. and Meth. B 149 31 - 37 1999
Joint Work
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Electrical resistivity of zirconium hydrides and deuterides at high temperatures Reviewed
A Kaneda, M Yamamoto, S Naito, M Mabuchi, T Hashino
JOURNAL OF PHYSICS-CONDENSED MATTER 10 ( 21 ) 4645 - 4657 1998
Single Work
Publisher：IOP PUBLISHING LTD
Electrical resistivity rho of zirconium hydrides ZrHx and deuterides ZrDx has been measured over the range of hydrogen concentration 0 less than or equal to x < 0.9 (x: H/Zr or D/Zr) and temperature 700 K less than or equal to T less than or equal to 1100 K. It has been found that rho increases linearly with x in the alpha phase and exhibits a parabolic change in the beta phase, shows almost no difference for H and D in the range 0 less than or equal to x < 0.9 and deviates from Matthiessen's rule in the alpha phase. To help discuss the findings, we have made energy band calculations of ZrHx and computed quantities that are closely related to rho. The observed change in rho with x can be explained by assuming that H atoms form independent electron scatterers in the alpha phase and H atom vacancies additionally form electron scatterers in the beta phase. The lack of difference observed in rho for H and D can be explained by the fact that electron-optical phonon coupling constant obtained from the energy band calculations is much smaller than the electron-acoustic phonon coupling constant. It is difficult to give a reasonable explanation of the deviation from Matthiessen's rule only by the energy band calculation result.
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Surface Electron Distribution by Fast Ion-Surface Scattering Reviewed
YAMAMOTO Masahiro
Scanning Microscopy 30 217 1998
Single Work
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High-temperature diffusion of hydrogen and deuterium in titanium and Ti3Al Invited Reviewed
Shizuo Naito, Masahiro Yamamoto, Minoru Doi, Masao Kimura
Journal of the Electrochemical Society 145 ( 7 ) 2471 - 2475 1998
Single Work
Publisher：Electrochemical Society Inc.
Diffusion coefficients (DH and DD) of hydrogen (H) and deuterium (D) in β-titanium (Ti) and β-Ti3Al have been obtained from the rates of gaseous H and D absorption by samples in the temperature ranges of 1173 to 1473 K for β-Ti and 1423 to 1523 K for β-Ti3Al. Activation energies for diffusion (∈d) are found to be 0.26 eV in β-Ti and 0.39 eV in β-Ti3Al, which are smaller than those corresponding to α-Ti and α-Ti3Al. Ratios DD/DH in β-Ti and β-Ti3Al are found to be larger than the classical value, 1/√2, and those in α-Ti and α-Ti3Al. The observed smaller ∈d in β-Ti than in α-Ti is due to the difference between the body-centered cubic structure of β-Ti and the hexagonal close-packed structure of α-Ti and the observed larger DD/DH in β-Ti than in α-Ti due to phonon-assisted jumps of diffusing H atoms in β-Ti. The observed smaller ∈d in β-Ti3Al than in α-Ti3Al can be explained by the body-centered cubic structure of β-Ti3Al and the random distribution of aluminum atoms in it, and the larger DD/DH in β-Ti3Al than in α-Ti, α-Ti3Al, and β-Ti by the presence of aluminum atoms as well as by the phonon-assisted H-atom jumps.
DOI： 10.1149/1.1838662
Other Link： https://iopscience.iop.org/article/10.1149/1.1838662/pdf
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Auger electron spectroscopy and electron energy loss spectroscopy study of the adsorption of nitrogen on a polycrystalline zirconium surface Reviewed
M Kurahashi, M Yamamoto, M Mabuchi, S Naito
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS 15 ( 5 ) 2548 - 2552 1997
Single Work
Publisher：AMER INST PHYSICS
Auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS) were used to investigate the adsorption of nitrogen gas on a polycrystalline zirconium surface at room temperature. it was found that the adsorption of nitrogen is saturated at an exposure of similar to 10 L, the thickness of the nitride formed on the specimen surface is 0.4-0.5 nm at a nitrogen exposure of 100 L, and the surface has the same large electronic density of states 4-5 eV below the Fermi energy as ZrN, The measured AES and EELS spectra are consistent with the electronic structure calculated for the Zr(0001)-(1X1)-N structure. (C) 1997 American Vacuum Society.
DOI： 10.1116/1.580768
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Vibrational Properties of a Polycrystalline Titanium Surface Studied by Electron Energy-Loss Fine Structure(EELFS) Analysis Reviewed
M. Kurahashi, M. Yamamoto, M. Mabuchi, S. Naito
J. Surf. Anal. 3 ( 2 ) 451 - 457 1997
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Theoretical study of nitrogen adsorption on Zr(0001) surface Reviewed
M. Yamamoto, M. Kurahashi, C. T. Chan, K. M. Ho, S. Naito
Surface Science 387 ( 1-3 ) 300 - 311 1997
Single Work
Authorship：Lead author, Corresponding author Publisher：ELSEVIER SCIENCE BV
The chemisorption of nitrogen on the zirconium (0001) surface has been investigated by first-principles total-energy and force calculations. Our results show that nitrogen adsorption at subsurface octahedral sites is energetically more favorable than at surface sites. The calculated binding energy, surface relaxation, work function and electronic structure are in good agreement with available experimental results. © 1997 Elsevier Science B.V.
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Surface channeling of fast ions Reviewed
Michi-Hiko Mannami, Kenji Kimura, Kazumasa Narumi, Masahiro Yamamoto, Shizuo Naito
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms 125 ( 1/4 ) 97 - 101 1997
Single Work
Publisher：Elsevier
Fast ions incident at glancing angles on single crystal surfaces are reflected from the surface, and the ion-surface interactions take place while the ions are outside of the solid. Our studies of ion-surface interactions performed at this scattering geometry are reviewed with a particular emphasis on the resonant coherent excitation (Okorokov excitation) of surface-channeled MeV B ions and the energy losses of low-velocity ions which are related to the electron density distribution outside the surface.
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Structure of the metal-liquid interface: self-consistent combination of the first-principles metal calculation and an integral equation method Reviewed
M Yamamoto, M Kinoshita
CHEMICAL PHYSICS LETTERS 274 ( 5/6 ) 513 - 517 1997
Single Work
Authorship：Lead author, Corresponding author Publisher：ELSEVIER SCIENCE BV
This letter contributes to development of microscopic theories for the metal/liquid interface. We report results of the first attempt to combine the first-principles calculation for the metal surface and the reference hypernetted-chain method for the liquid in a fully self-consistent manner. The dipolar liquid/Pt(111) interface is considered. The electron density, liquid structure, and electrostatic potential across the interface are briefly discussed. (C) 1997 Published by Elsevier Science B.V.
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Dependence of the third-order coefficients in Landau free energies for bcc->fcc structural transition on hydrogen concentration in zirconium hydrides Reviewed
Y Ashida, M Yamamoto, S Naito, M Mabuchi, T Hashino
JOURNAL OF APPLIED PHYSICS 82 ( 3 ) 1072 - 1079 1997
Single Work
Publisher：AMER INST PHYSICS
Young's modulus E and the modulus of rigidity G of zirconium hydrides ZrHx(0.9 less than or equal to x less than or equal to 1.65) at 941 and 1001 K have been obtained as a function of hydrogen concentration c by measuring resonance frequencies for bending and torsion vibrations of a polycrystalline wire. As c increases, observed E and G increase in the bcc beta phase, slightly increase linearly in the beta + delta phase, and then decrease in the fcc delta phase. On the basis of a phenomenological free energy in terms of strain components taking account of space group symmetry, two types of Landau expansion of the free energies for the beta phase in terms of the strain components which play an important role in the structural phase transition between the beta and the delta phases are examined. The observed E and G are assumed to be the same as the second-order coefficients of the free energy for the Bain distortions, which occur at the structural phase transition. The dependence of the third-order coefficients on c permits the expanded frets energies to describe the fact that the beta phase is more stable than the delta phase at low c. (C) 1997 American Institute of Physics.
DOI： 10.1063/1.365873
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Yuh Ashida, Masahiro Yamamoto, Shizuo Naito, Mahito Mabuchi, Tomoyasu Hashino
Journal of Applied Physics 80 ( 6 ) 3254 - 3258 1996.9
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Yuh Ashida, Masahiro Yamamoto, Shizuo Naito, Mahito Mabuchi, Tomoyasu Hashino
Journal of Applied Physics 80 ( 6 ) 3259 - 3266 1996.9
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First-principles calculation of the longitudinal phonon in the surface-normal direction of a zirconium(0001) slab: Localization mode at the subsurface Reviewed
M Yamamoto, CT Chan, KM Ho, M Kurahashi, S Naito
PHYSICAL REVIEW B 53 ( 20 ) 13772 - 13776 1996
Single Work
Publisher：AMERICAN PHYSICAL SOC
The energies and amplitudes of the longitudinal vibrational mode in the surface-normal [0001] direction of the fully relaxed zirconium slab with a (0001) surface are calculated with force constants determined from first-principles total-energy and force calculations. A subsurface vibrational mode with frequency above the bulk continuum is found. We attribute the origin of this mode to the hardness of the force constant between the surface and the second layer.
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Masahiro Yamamoto, C. T. Chan, K. M. Ho, Shizuo Naito
Physical Review B 54 ( 19 ) 14111 - 14120 1996
Single Work
Authorship：Lead author Publisher：American Physical Society (APS)
DOI： 10.1103/PhysRevB.54.14111
Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.54.14111/fulltext
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Naito S, Yamamoto M, Miyoshi T, Mabuchi M, Doi M, Kimura M
Journal of the Chemical Society - Faraday Transactions 92 ( 18 ) 3407 - 3410 1996
Joint Work
Publisher：Royal Society of Chemistry (RSC)
DOI： 10.1039/ft9969203407
Other Link： http://orcid.org/0000-0001-8645-2224
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Diffusion of hydrogen in titanium, Ti<inf>88</inf>Al<inf>12</inf>and Ti<inf>3</inf>Al Reviewed
Miyoshi T, Naito S, Yamamoto M, Doi M, Kimura M
Journal of the Chemical Society - Faraday Transactions 92 ( 3 ) 483 - 486 1996
Joint Work
Publisher：Royal Society of Chemistry (RSC)
DOI： 10.1039/ft9969200483
Other Link： http://orcid.org/0000-0001-8645-2224
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Dissolution of hydrogen and deuterium in titanium, Ti94Al6 and Ti3Al Reviewed
Shizuo Naito, Masahiro Yamamoto, Minoru Doi, Masao Kimura
Journal of the Chemical Society, Faraday Transactions 91 ( 13 ) 1967 - 1973 1995
Single Work
The solubility of hydrogen and deuterium in α-, α,β- and β-titanium, Ti94Al6 and in α2-Ti3Al has been volumetrically measured in the ranges of temperature 623-1323 K and hydrogen concentration (atomic ratio) 0.001-0.25. The equilibrium hydrogen pressure at a given temperature and hydrogen concentration has been found to increase greatly as the aluminium content increases. This is explicable on the assumption that aluminium atoms block some of the sites available to hydrogen atoms. In contrast, the heat of solution of hydrogen only slightly increases with the aluminium content and in α-titanium, α-Ti94Al6 and α2-Ti3Al, the ratio of the deuterium pressure to the hydrogen pressure at identical hydrogen and deuterium concentrations is almost independent of the aluminium content. A possible cause of the small dependence of the measured heat and ratio on the aluminium content is discussed and occupation of the tetrahedral site by hydrogen atoms is suggested for α-titanium, α-T94Al6 and α2-Ti3Al. The origin of the sloping plateaus observed in the pressure-composition isotherms for α, β-Ti94Al6 is also briefly discussed.
DOI： 10.1039/ft9959101967
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First-principles calculation of oxygen adsorption on Zr(0001) surface : Possible site occupation between the second and the third layer Reviewed
YAMAMOTO Masahiro
Bull. Amer. Phys. Soc. 40 ( 1 ) 164 1995
Single Work
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ELECTRON-ENERGY-LOSS SPECTRA AND SECONDARY-ELECTRON EMISSION-SPECTRA OF ZR, ZRN AND ZRO2 Reviewed
M KURAHASHI, M YAMAMOTO, M MABUCHI, S NAITO
JOURNAL OF PHYSICS-CONDENSED MATTER 7 ( 24 ) 37 - 4772 1995
Single Work
Publisher：IOP PUBLISHING LTD
Electron energy-loss spectra and secondary-electron emission spectra have been measured for Zr, ZrN and ZrO2. The position and shape of the measured peaks associated with 4p-electron excitation are consistent with the multiplets calculated for zirconium ions possible in Zr, ZrN and ZrO2.
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Electron energy loss spectra of Sc, Ti, V and their oxides Reviewed
M. Kurahashi, M. Yamamoto, S. Naito
Journal of Physics: Condensed Matter 7 ( 35 ) L463 - L468 1995
Single Work
Electron energy loss spectra have been investigated for Sc, Ti, V and their oxidized surfaces. The position and shape of the measured peaks associated with the 3p electron excitation are found to be consistent with 3p63da4sm-3p53dn+14s m transitions calculated for isolated Sc, Ti and V ions.
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ELECTRON ENERGY-LESS FINE-STRUCTURE OF A POLYCRYSTALLINE TITANIUM SURFACE Reviewed
M KURAHASHI, M YAMAMOTO, M MABUCHI, S NAITO
JOURNAL OF PHYSICS-CONDENSED MATTER 7 ( 1 ) 37 - 46 1995
Single Work
Publisher：IOP PUBLISHING LTD
The temperature dependence of the electron energy-loss fine structure (EELFS) of a polycrystalline titanium surface has been measured in reflection mode for electron beams at different incidence angles to the normal of the surface. We have found that within experimental error (about 0.06 Angstrom) the interatomic distance between titanium atoms remains unchanged as the depth from the surface changes and that the EELFS Debye-Waller factor has larger values for larger incidence angles. This result is compared with the reported results of LEED measurements.
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Naito S, Yamamoto M, Doi M, Kimura M
Journal of the Chemical Society, Faraday Transactions 91 ( 22 ) 4143 - 4147 1995
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FIRST-PRINCIPLES CALCULATIONS OF THE SURFACE RELAXATION AND ELECTRONIC-STRUCTURE OF ZR(0001)
M YAMAMOTO, CT CHAN, KM HO
PHYSICAL REVIEW B 50 ( 11 ) 7932 - 7939 1994.9
Joint Work
Publisher：AMERICAN PHYSICAL SOC
The multilayer relaxations of the Zr(0001) surface and the surface electronic structure are studied using first-principles total-energy and force calculations. The distance between the outermost two layers is 4.4-4.7% smaller than the ideal interlayer spacing, while inner layers show oscillatory relaxations. We examined two possible termination sequences for the surface and found that the hcp surface termination is more stable by about 0.06 eV per surface atom as compared to the fee terminated structure. We observed an increase in the local density of states (LDOS) for the surface atoms around the Fermi level relative to the bulk atoms. The increase in the LDOS is found to be closely related to the existence of surface states and resonances around the Fermi level.
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A Theoretical Model for the several Common Stacked Crystals in Arrangement of the stacking sequence of Parallel Atomic Layers in a Simple Crystal Solid Reviewed
Masao Kimura, Masahiro Yamamoto, Mahito Mabuchi, Tomoyasu Hashino
J. Phys. Soc. Japan 63 ( 10 ) 3661 - 3670 1994
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Structural Transition between HCP and FCC Structures with Considering Configurations of the Position Vectors Defined by Several Common Stacked Model Hamiltonian Reviewed
Masao Kimura, Masahiro Yamamoto, Mahito Mabuchi, Tomoyasu Hashino
J. Phys. Soc. Japan 63 ( 10 ) 3714 - 3728 1994
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SOLUBILITY OF HYDROGEN AND DEUTERIUM IN TI3AL Reviewed
M KIMURA, T TSUCHIYAMA, S NAITO, M YAMAMOTO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 90 ( 9 ) 1355 - 1356 1994
Single Work
Publisher：ROYAL SOC CHEMISTRY
The solubility of hydrogen and deuterium in Ti3Al has been measured and found to obey Sieverts law. The difference in the solubility between hydrogen and deuterium can be explained by a model in which hydrogen and deuterium atoms perform harmonic oscillations in the tetrahedral site of the Ti3Al crystal lattice.
DOI： 10.1039/ft9949001355
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HIGH-TEMPERATURE DIFFUSION OF HYDROGEN AND DEUTERIUM IN PALLADIUM Reviewed
T MAEDA, S NAITO, M YAMAMOTO, M MABUCHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 90 ( 6 ) 899 - 903 1994
Single Work
Publisher：ROYAL SOC CHEMISTRY
The diffusivity of hydrogen and deuterium in palladium has been measured at temperatures between 773 and 1373 K and at hydrogen and deuterium concentrations less than 10(-4) H/Pd and D/Pd (atomic ratio). The measured diffusion coefficients for hydrogen (D(H)) and deuterium (D(D)) showed Arrhenius behaviour. The dependence of the ratio D(D)/D(H) on temperature has been explained by a model of diffusion in which a hydrogen atom in an octahedral site of the palladium lattice can jump into the adjacent octahedral site only when local deformation of the palladium lattice assists the jump.
DOI： 10.1039/ft9949000899
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First-principles calculations of the surface relaxation and electronic structure of Zr(0001) Reviewed
Masahiro Yamamoto, C. T. Chan, K. M. Ho
Physical Review B 50 ( 11 ) 7932 - 7939 1994
Single Work
Authorship：Lead author
The multilayer relaxations of the Zr(0001) surface and the surface electronic structure are studied using first-principles total-energy and force calculations. The distance between the outermost two layers is 4.44.7 % smaller than the ideal interlayer spacing, while inner layers show oscillatory relaxations. We examined two possible termination sequences for the surface and found that the hcp surface termination is more stable by about 0.06 eV per surface atom as compared to the fcc terminated structure. We observed an increase in the local density of states (LDOS) for the surface atoms around the Fermi level relative to the bulk atoms. The increase in the LDOS is found to be closely related to the existence of surface states and resonances around the Fermi level. © 1994 The American Physical Society.
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EFFECTS OF HYDROGEN AND DEUTERIUM CONCENTRATION ON MEASUREMENTS OF THE SOLUBILITY AND DIFFUSIVITY OF HYDROGEN ISOTOPES IN YTTRIUM Reviewed
T MAEDA, S NAITO, M YAMAMOTO, M MABUCHI
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 90 ( 13 ) 1979 - 1982 1994
Single Work
Publisher：ROYAL SOC CHEMISTRY
The solubility and diffusivity of hydrogen and deuterium in polycrystalline alpha-yttrium have been measured in the temperature range 1073-1273 K and at hydrogen and deuterium concentrations, theta (H:Y and D:Y, atomic ratio), of 0-0.44. The measured solubility obeys the relationship p = k[theta/(1-theta)]2, where p is the hydrogen pressure and k is a constant independent of theta. The measured diffusion coefficients for hydrogen and deuterium increased with theta. The experimental result has been explained by a model in which a hydrogen atom can occupy a pair of two nearest-neighbour tetrahedral sites of the hcp alpha-yttrium lattice and move almost freely between the two sites.
DOI： 10.1039/ft9949001979
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DIFFUSION OF HYDROGEN IN TI3AL Reviewed
S NAITO, O HASHITOMI, M YAMAMOTO, Y BABA, M KIMURA
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 90 ( 16 ) 2423 - 2424 1994
Single Work
Publisher：ROYAL SOC CHEMISTRY
The diffusivity of hydrogen in the intermetallic compound Ti3Al has been measured in the temperature range 973-1323 K. The activation energy for diffusion has been found to be nearly twice those for pure Ti and Al. A possible origin of this large activation energy is the presence of ordered Al atoms in Ti3Al and the difference in the heat of solution of hydrogen between Ti and Al.
DOI： 10.1039/ft9949002423
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AUGER-ELECTRON, ELECTRON-ENERGY-LOSS, SECONDARY-ELECTRON EMISSION AND SECONDARY-ION MASS SPECTROSCOPIC STUDIES ON THE OXIDATION OF HAFNIUM AT ROOM-TEMPERATURE Reviewed
T SATAKE, M YAMAMOTO, S NATIO, M MABUCHI, A KANEDA, M KURAHASHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 89 ( 19 ) 3611 - 3618 1993
Single Work
Publisher：ROYAL SOC CHEMISTRY
Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), secondary electron emission spectroscopy (SES) and secondary ion mass spectrometry (SIMS) have been used to investigate the oxidation of a hafniun surface at room temperature (298 K). The change in the electronic energies of the core and valence levels with the oxidation is discussed on the basis of the comparison between the observed spectra and the electronic structures calculated for a hafnium atom, ion, bulk metal and bulk oxide. The growth of oxide films to a thickness of ca. 1.5 nm is found from the decay in the intensity of Auger electrons emitted by the metal substrate and from the depth profile ot the SIMS spectra.
DOI： 10.1039/ft9938903611
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DIFFUSIVITY AND SOLUBILITY OF HYDROGEN AND DEUTERIUM IN YTTRIUM Reviewed
T MAEDA, S NAITO, M YAMAMOTO, M MABUCHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 89 ( 24 ) 4375 - 4379 1993
Single Work
Publisher：ROYAL SOC CHEMISTRY
The diffusivity and solubility of hydrogen and deuterium in polycrystalline alpha-yttrium have been measured in the temperature range 1073-1373 K. The ratios of the measured diffusion coefficient of deuterium to that of hydrogen showed the classical value 1/square-root 2. The activation energy of diffusion has been found to be 510 meV for both hydrogen and deuterium. The differences in the solubility and diffusivity between hydrogen and deuterium have been explained by using rate theory and assuming that hydrogen and deuterium atoms in yttrium are slightly anharmonic oscillators.
DOI： 10.1039/ft9938904375
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ADSORPTION POTENTIAL OF HYDROGEN-ATOM ON ZIRCONIUM Reviewed
M YAMAMOTO, S NAITO, M MABUCHI, T HASHINO
JOURNAL OF PHYSICAL CHEMISTRY 96 ( 8 ) 3409 - 3412 1992
Single Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
The adsorption potential of hydrogen atom on zirconium(0001) surface has been calculated by an effective medium theory. The adsorption energy is found to be -3.0 eV for both the overlayer sites above the tetrahedral site and the octahedral site. The hydrogen vibrational energy and the potential energy including an effect of lattice relaxation at the subsurface tetrahedral site are in good agreement with experiments.
DOI： 10.1021/j100187a042
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RELATIVISTIC SELF-CONSISTENT CALCULATION FOR HAFNIUM ATOMS AND IONS BASED ON A RELATIVISTIC LOCAL DENSITY FUNCTIONAL THEORY Reviewed
M YAMAMOTO, M MABUCHI, S NAITO
JOURNAL OF PHYSICAL CHEMISTRY 96,10784 ( 26 ) 10784 - 10788 1992
Single Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
The Dirac equation for the spherical symmetrical potential of hafnium atoms and ions with various electron configurations has been calculated numerically by using a relativistic local density functional approximation. Electron binding energies, ionization potential, X-ray emission energies, and Auger electron energies are evaluated by the total energy difference (DELTASCF) method and Slater's transition-state method. The calculated results are in agreement with the experimental results measured by spectroscopies.
DOI： 10.1021/j100205a036
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Mechanism of oxygen absorption by zirconium
Masahiro Yamamoto
1991.3
Single Work
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AUGER-ELECTRON, ELECTRON-ENERGY LOSS AND SECONDARY-ELECTRON EMISSION SPECTROSCOPIC STUDIES ON THE OXIDATION OF ZIRCONIUM AT HIGH-TEMPERATURES AND ROOM-TEMPERATURE Reviewed
M YAMAMOTO, S NAITO, M MABUCHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 87 ( 10 ) 1591 - 1599 1991
Single Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
Auger electron (AES), electron energy loss (EELS) and secondary electron emission spectroscopy (SES) have been used to investigate the surface oxidation of zirconium at room temperature and high temperatures, 773-973 K, under low oxygen pressures 1.3 x 10(-5)-1.3 x 10(-3) Pa. The kinetic energies of the Auger and the secondary electrons and the electron energy losses by single electron excitations are explained by the electronic structure in the core and the valence states of the metal and the oxide of zirconium. The energy loss by the collective excitation of plasmon is also observed in the EELS measurement for the metal and the oxide surface. The increase in the relative peak-to-peak height of the oxygen Auger transition and of the zirconium Auger transition by oxidation at high temperatures does not depend simply on the oxygen exposure represented by the product of oxygen pressure and exposure time, i.e. exposure in Langmuir, because of the dynamic competition between surface processes and the diffusion process of oxygen into the bulk. The rate of oxide growth is found to be parabolic at high temperature (773 K) and at 1.3 x 10(-5) Pa.
DOI： 10.1039/ft9918701591
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CHANGE IN THE WORK FUNCTION OF ZIRCONIUM BY OXIDATION AT HIGH-TEMPERATURES AND LOW OXYGEN PRESSURES Reviewed
Y MAENO, M YAMAMOTO, S NAITO, M MABUCHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 87 ( 9 ) 1399 - 1403 1991
Single Work
Publisher：ROYAL SOC CHEMISTRY
Changes in the work function of zirconium on oxidation are measured at oxygen pressures of 3.0 x 10(-6)-3.0 x 10(-4) Pa and at temperatures in the range 426-775 K. The work function first decreases then increases until a final saturation stage is reached. Use of secondary-ion mass spectroscopy (SIMS) shows that the changes correspond to oxygen adsorption, oxide nucleation and oxide growth, respectively. The initial decrease in work function is interpreted by the incorporation of oxygen adatoms into the subsurface. The oxygen adsorption potential of zirconium is evaluated by an effective medium theory, and the physical origin of the incorporation of oxygen adatoms is discussed. The positive change in the work function caused by oxide formation and the temperature and pressure dependences of the change in the work function by oxidation are explained qualitatively.
DOI： 10.1039/ft9918701399
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ANOMALY IN THE RATE OF OXYGEN ABSORPTION BY ZIRCONIUM DUE TO THE FORMATION OF OXIDE AT THE SURFACE - AUTOCATALYTIC REACTION MODEL OF OXIDE NUCLEATION Reviewed
M YAMAMOTO, S NAITO, M MABUCHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 86 ( 22 ) 3797 - 3802 1990
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SOLUBILITY AND DIFFUSIVITY OF HYDROGEN AND DEUTERIUM IN ALPHA-HAFNIUM AT HIGH-TEMPERATURES Reviewed
S NAITO, M YAMAMOTO, T HASHINO
JOURNAL OF PHYSICS-CONDENSED MATTER 2 ( 8 ) 1963 - 1970 1990
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INCREASE IN YIELDS OF SECONDARY IONS BY OXIDATION OF ZIRCONIUM AT HIGH-TEMPERATURES AND LOW OXYGEN PRESSURES Reviewed
M YAMAMOTO, S NAITO, M MABUCHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 86 ( 1 ) 157 - 164 1990
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KINETICS OF OXYGEN ABSORPTION BY ALPHA-ZIRCONIUM Reviewed
M YAMAMOTO, S NAITO, M MABUCHI, T HASHINO
JOURNAL OF PHYSICAL CHEMISTRY 93 ( 13 ) 5203 - 5209 1989
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PRESSURE-DEPENDENCE OF OXYGEN ABSORPTION BY METALLIC ZIRCONIUM WITH A CLEAN SURFACE Reviewed
H TAKEUCHI, S NAITO, M YAMAMOTO, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS I 84 ( 12 ) 4235 - 4247 1988