Papers - YAMAMOTO Masahiro
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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