論文 - 山本 雅博
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Yuko YOKOYAMA, Takaaki NAGAI, Akimitsu ISHIHARA, Masahiro YAMAMOTO, Kohei MIYAZAKI, Takeshi ABE, Kenji KANO
Electrochemistry 90 ( 10 ) 103003 - 103003 2022年9月
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Reciprocal Sum Expression for Steady-state Kinetics —Enzyme Reactions and Voltammetry— 査読あり
Yuko YOKOYAMA, Masahiro YAMAMOTO, Kohei MIYAZAKI, Takeshi ABE, Kenji KANO
Electrochemistry 90 ( 10 ) 103002 - 103002 2022年7月
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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 査読あり
Takashi Kakiuchi, Shota Domae, Taishi Miyadi, Kaito Kibi, Masahiro Yamamoto
ELECTROCHEMISTRY COMMUNICATIONS 126 2021年5月
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出版者・発行元：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 招待あり 査読あり
Takashi Kakiuchi, Masaki Hisazumi, Yasufumi Moriyama, Masahiro Yamamoto
Electrochemistry Communications 124 106953 2021年3月
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Tailored Photoluminescence Properties of Ag(In,Ga)Se2 Quantum Dots for Near-Infrared In Vivo Imaging 査読あり
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年2月
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Ryo Murakami, Syuji Kobayashi, Manami Okazaki, Alexander Bismarck, Masahiro Yamamoto
Frontiers in Chemistry 6 2018年9月
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Treatment of oral cancer using magnetized paclitaxel 査読あり 国際共著
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年3月
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A model of the potential-dependent adsorption of charged redox-active species at the electrode surface 査読あり
Yuki Kitazumi, Osamu Shirai, Masahiro Yamamoto, Kenji Kano
Electrochimica Acta 259 542 - 551 2018年1月
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Treatment of oral cancer using magnetized paclitaxel 査読あり 国際共著
R. Nakakaji et al.
Oncotarget 2018年
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Electrochemical Sensing of Neurotoxic Agents Based on Their Electron Transfer Promotion Effect on an Au Electrode 査読あり
Hiroshi Shimada, Shiori Noguchi, Masahiro Yamamoto, Katsuhiko Nishiyama, Yusuke Kitamura, Toshihiro Ihara
ANALYTICAL CHEMISTRY 89 ( 11 ) 5743 - 5748 2017年6月
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出版者・発行元：AMER CHEMICAL SOC
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(3) from Desulfovibrio vulgaris Miyazaki F 査読あり
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年5月
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出版者・発行元：ELSEVIER SCIENCE BV
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 (H(2)ase) to cytochrome (cyt) c(3) 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 H(2)ase and cyt c(3) 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 H(2)ase at which the electron transfer from H(2)ase to cyt c(3) 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 H(2)ase/cyt c(3) 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 H(2)ase/cyt c(3) complex overcomes the destabilization derived from the electrostatic repulsion of the overall positive charge of both proteins. (C) 2017 Elsevier B.V. All rights reserved.
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Electrochemical Sensing of Neurotoxic Agents Based on Their Electron Transfer Promotion Effect on an Au Electrode 査読あり
Hiroshi Shimada, Shiori Noguchi, Masahiro Yamamoto, Katsuhiko Nishiyama, Yusuke Kitamura, Toshihiro Ihara
Anal. Chem. 2017年
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Magnetic metal complex-conducting copolymer core-shell nanoassemblies for single-drug anticancer platform 査読あり
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年
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“Electrostatic roles in electron transfer from [NiFe] hydrogenase to cytochrome c3 from Desulfovibrio vulgaris Miyazaki F 査読あり
Yu Sugimoto, Yuki Kitazumi, Osamu Shirai, Koji Nishikawa, Yoshiki Higuchi, Masahiro Yamamoto, Kenji Kano
BBA - Proteins and Proteomics 2017年
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Magnetic metal-complex-conducting copolymer core-shell nanoassemblies for a single-drug anticancer platform 査読あり
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年
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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 査読あり
Ryutaro Katsube, Yuki Kitazumi, Osamu Shirai, Masahiro Yamamoto, Kenji Kano
Journal of Electroanalytical Chemistry 780 114 - 118 2016年11月
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© 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年5月
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© 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 査読あり
Yu Sugimoto, Yuki Kitazumi, Osamu Shirai, Masahiro Yamamoto, Kenji Kano
JOURNAL OF PHYSICAL CHEMISTRY B 120 ( 12 ) 3122 - 3128 2016年3月
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出版者・発行元：AMER CHEMICAL SOC
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 degrees (k degrees 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 degrees values well reproduced the experimental data. In conclusion, k/k degrees can be predicted by PB-based simulation as long as the crystal structure of the enzyme and the substrate binding site are known.
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Potentiometric coulometry using a liquid-film-modified electrode as a reversible surfaceconfined system”, J. Electroanal. Chem. 2016, 780, 査読あり
Ryutaro Katsube, Yuki Kitazumi, Osamu Shirai, Masahiro Yamamotob, Kenji Kano
J. Electronal. chem. 2016年
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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 査読あり
Masahiro Yamamoto, and Kenji Kano
J. Phys. Chem. 2016年
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