Search

Your search keyword '"Uematsu, Kohei"' showing total 32 results
Start Over Author "Uematsu, Kohei" Search Limiters Full Text
32 results on '"Uematsu, Kohei"'

27. A Theoretical Approach to the Fluorophilicity of Ions viathe Gibbs Energy of Ion Transfer at the Fluorous Solvent/Water Interface

Author

Osakai, Toshiyuki, Kato, Takeshi, Eda, Kazuo, Uematsu, Kohei, and Katano, Hajime

Abstract

The non-Bornian solvation model has been applied to a theoretical consideration of the Gibbs free energy for the transfer of fluorinated anions, non-fluorinated cations, and non-fluorinated anions at the 2H,3H-decafluoropentane (DFP)/water (W) and 1,2-dichloroethane (DCE)/W interfaces. According to our previous experimental results, the fluorinated anions are more stable in DFP than DCE, while the non-fluorinated cations and anions are less stable in DFP. To understand this characteristic feature of DFP, energy decomposition analyses have been performed for the hypotheticaltransfer of ions at the DFP/DCE interface. In conclusion, the characteristics of DFP as a fluorous solvent should be explained in terms of the higher repulsive interaction of the solvent molecule with ions, particularly with non-fluorinated ions.

Published
2021
Full Text
View/download PDF

30. Voltammetric study of adsorption layers of various 4-pyridyl terminated surfactants on a Au(1 1 1) electrode: Effects of electronic property of pyridyl group and intermolecular hydrogen bonding upon potential-driven phase changes

Author

Uematsu, Kohei, Sagara, Takamasa, Uematsu, Kohei, and Sagara, Takamasa

Abstract

The major factors determining the potential-driven phase changes of the films of 4-pyridyl terminated water-insoluble neutral surfactants on a Au(111) electrode were described using the results of dc and ac voltammetric measurements. In total six surfactants were used to elucidate the effects of electronic property of the 4-pyridyl head group, hydrogen bonding ability between amide groups, direction of the amide bond, and bulkiness around the head group upon the potential dependent reorientation and adsorption-desorption processes.Comparison of the behavior of pentadecyl 4-pyridyl ether (C15-O-Py) and 1-pyridin-4-yl-hexadecan-1-one (C15-(C=O)-Py), possessing respectively, the highest and lowest excess electronic charge on the pyridyl nitrogen among the six surfactants, revealed that the latter exhibits more distinct reorientation of pyridyl group corresponding to phase transition between condensed and loose-packed states and narrower potential region of the compact film formation. Introduction of amide group in the alkyl chains of the surfactants reduced the packing of the adsorbed film in the potential region of the compact film formation,as evidenced by an increase of the differential capacitance. It was found that the existence of amide group facilitates the potential-driven phase transition of closely packed film from a condensed state to a loosely packed state, whereas it suppresses the transition of loosely packed film. The concomitant steric effect was also discussed., Journal of Electroanalytical Chemistry, 623(1), pp.109-119; 2008

Published
2008

32. Decomposition of free chlorine with tertiary ammonium.

Author

Katano H, Uematsu K, Tatsumi H, and Tsukatani T

Subjects
Chloramines analysis, Electrodes, Platinum chemistry, Surface Properties, Anion Exchange Resins chemistry, Chlorine analysis, Quaternary Ammonium Compounds chemistry
Abstract

The reaction of free chlorine with tertiary ammonium or amine compounds in aqueous solution was studied by the amperometry at a rotating Pt-disk electrode. The amperometric method can be applied to follow the concentration of free chlorine (c(Cl)) even in the presence of chloramine species. By addition of mono- and dibutylammonium to the solution containing free chlorine, the step-like decrease in c(Cl) was observed, indicating the rapid formation of the stable chloramine species. By addition of tributylammonium, the c(Cl) was decreased exponentially to nearly zero even if the free chlorine was present initially in excess. The c(Cl)-t curves can be explained by tributylammonium-species-catalyzed decomposition of free chlorine to chloride ion. The catalytic decomposition was observed also with the tertiary-ammonium-based anion-exchange resins. Furthermore, the anion-exchange resins exhibited the decomposition of not only free chlorine but also chloramines in water.

Published
2010
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results