記述言語：英語   出版者・発行元：AMER CHEMICAL SOC  

A novel zwitterionic surfactant, N-dodecyl-N,N,N',N'-tetramethylethylenediammoniopropanesulfonate bromide (DEPB), has been synthesized, and Br- involved in the micellar system has been characterized by potentiometry, NMR, and X-ray absorption fine structure (XAFS). Although the dissociation degree of Br- from the micelle evaluated by potentiometry almost agrees with that determined by NMR, the former is significantly smaller than the latter over the entire range of concentrations of DEPB. This is explained by assuming that the bromide ions in the micellar system have several different peripheral structures. XAFS has given significant insight into the hydration structures of Br- involved in the system. Some of the bromide ions partitioned into the micelle are dehydrated and are directly bound by the ammonium groups in the DEP molecules. However, some of the bromide ions are still completely hydrated even when they are partitioned into the micelles. The average hydration number of the bromide ions directly bound by the ammonium groups was determined to be similar to 3.3. The partial dehydration of Br- is possibly facilitated by the characteristic hydration circumstances provided by the charge-stacked structure of the surfactant and by the resulting thick palisade layer of the DEP micelle.

DOI： 10.1021/la701145q

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記述言語：英語   出版者・発行元：AMER CHEMICAL SOC  

Solvation of ions in concentrated aqueous poly(ethylene glycol) (PEG) has been studied from thermodynamic and structural viewpoints using ion-transfer voltammetry at the interface between aqueous and nitrobenzene phases and X-ray absorption fine structure (XAFS). Systematic changes in the ion-transfer potential from water to aqueous PEG have been confirmed for several ions relative to the corresponding potential of tetraethylammonium ion (Et4N+), which is almost independent of PEG concentration. The results obtained for alkali cations strongly suggest the involvement of their complexation with PEG even in relatively diluted PEG solutions. It has been implied that the solvation circumstances of Br- and ClO4- are drastically altered when the PEG concentration becomes higher than particular critical values (e.g., 30-50% PEG200), where free water molecules are diminished because of the hydration of PEG. XAFS measurements have also been performed for K+ and Br- to get direct evidence for these findings. Although the spectra at the K K-edge clearly indicate the presence of a PEG complex of K+ in relatively diluted PEG solutions (similar to 33% PEG200), an obvious increase in its ion-transfer potential has been detected at lower PEG concentrations, indicating that complexes formed at the interface rather than in bulk solution are transferred into an organic phase. Br- is fully hydrated in 0-50% PEG solutions, whereas some water molecules are replaced by PEG when the PEG concentration increases. Increasing the PEG concentration causes decreases in the coordination number from 6 in water to 2-3 in neat PEG. Thus, the present approach not only has elucidated the structural and thermodynamic aspects of ionic solvation in aqueous PEG but also has provided the information of the hydration of PEG.

DOI： 10.1021/jp071666j

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DOI： 10.5182/jaie.18.150

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記述言語：英語  

The structures of 18-crown-6 (18C6) complexes with K+ and Rb+ in methanolic solutions have been studied by X-ray absorption fine structure (XAFS) at the Br K-edge as well as at the K and Rb K-edges. The XAFS spectrum at the K or Rb K-edge has indicated that either Br- or solvent (methanol) molecules are present in the first coordination shell of K+ or Rb+ complexed by 18C6. However, the spectra obtained at the Br-K edge have strongly suggested that the alkali cations do not exist in the vicinity of Br-, indicating that no direct ion-pairing occurs between the 18C6 complex and Br-. The 18C6-K+ complex maintains D 3d symmetry even in methanol, and two methanol molecules coordinate the cation possibly from above and below the crown plane. In contrast, the corresponding Rb+ complex possibly forms an umbrella-shaped complex, in which Rb+ is situated slightly off the crown plane and three solvent molecules bind With the cation. © 2006 Springer Science+Business Media, LLC.

DOI： 10.1007/s10953-006-9088-z

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記述言語：英語   出版者・発行元：AMER CHEMICAL SOC  

Teflon AF-2400 capillary has been used for capillary electrophoretic separation as well as for liquid-core waveguide for axial absorption detection. This separation/ detection scheme has allowed continuous monitoring of electrophoretically induced reactions. In this paper, the decomposition of Cd2+ complex with 4-(2-pyridylazo)resorcinol has been tested, and its decomposition kinetics has been studied. A simple modeling has predicted the single-exponential decay of the absorbance detected by the present axial absorption detector and has allowed the estimation of the decomposition rate constant for this reaction.

DOI： 10.1021/ac060175c

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記述言語：日本語   出版者・発行元：広信社  

CiNii Books

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記述言語：日本語   出版者・発行元：JAPAN SOC ANALYTICAL CHEMISTRY  

X-ray absorption fine structure (XAFS) is an efficient tool to probe the local structure of an absorbing atom, and has been applied to various samples. Although the total reflection of Xray has allowed us to study solid surfaces by XAFS, the accessibility of this approach to a solution surface has been restricted because of a difficulty to make precise measurements of X-ray absorption. We proposed a novel method, named total-reflection total-conversion-electron yield (TRTCY) XAFS, where the Auger electrons generated by X-ray absorption are detected with high sensitivity. The detection depth was typically < 10 rm, and the detection volume was 2 similar to 3 nl. Solution surfaces can be modified by monolayers, and model the various interfaces having separation, sensing, and molecular recognition functions. TRTCY-XAFS provides information on the local concentrations and structures of ions attracted by the surface monolayers from a sub-phase. The principle of this approach, the instruments used in a series of studies, and some obtained results are discussed in this review. In addition to our prototype instruments, a new version, which has allowed automatic control of the surface molecular density, is also outlined.

DOI： 10.2116/bunsekikagaku.52.405

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記述言語：英語  

The adsorption isotherms of Zn2+ and Br- on a zwitterionic surface monolayer and their local structures have been studied by total-reflection total-conversion helium ion yield X-ray absorption fine structure (TRTCYXAFS). The surface monolayer is prepared by spontaneous adsorption of N-dodecyl-N,N-dimethylammonio-butane sulfonic acid (DDABS) on an aqueous solution surface from a bulk solution. The adsorption of Zn2+ on the surface monolayer depends on the nature of coexistent anions
a poorly hydrated large anion such as ClO4- are well partitioned into the DDABS monolayer, and Zn2+ is attracted by generated negative potential. TRTCY-XAFS spectra indicate that Zn2+ attracted by the surface monolayer is mostly hydrated, but is partly bound by the sulfonic acid in DDABS, particularly when the large negative potential is induced by anion-partition. The TRTCY-XAFS spectra of Br- also imply the coexistence of hydrated Br- and that bound by the ammonium group in the surface monolayer. The calculation using FEFF, ver.7.02, suggests that the interaction distance between Br- and water in the surface monolayer (3.15 Å) is shorter than that in bulk water (3.20 Å). In the surface monolayer, the availability of water molecules is limited, and thus the second coordination shell cannot be formed around Br-. This weakens the interaction between water molecules, and results in the shorter coordination distance for Br-.

DOI： 10.1021/jp026248n

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記述言語：英語  

The local structures of Br- in ion-exchange resins are studied with XAFS at the Br-K edge. Br--form anion-exchange resins having different ion-exchange groups, i.e., tertiary ammonium (R-3) and quaternary ammonium ion (R-4), are examined after being soaked in water, methanol (MeOH), and some polar aprotic solvents. The resins soaked in aprotic solvents give almost the same spectral features as dry resins, indicating that Br- is tightly bound by the ion-exchange sites. Br- is entrapped inside the tripod composed of three equivalent methyl groups of the ion-exchange group in the R-4 resin, while it strongly interacts with the ammonium hydrogen of the ion-exchange group of the R-3 resin. In the latter case, the scattering from methyl and methylene carbon atoms in the ion-exchange group also contributes to XAFS spectra. In contrast, characteristic features are confirmed when the resins are soaked in water and MeOH. Detailed analyses of XAFS spectra imply that two species, i.e., solvated Br- and that bound on the ion-exchange sites, coexist in the resins soaked in protic solvents. The XAFS spectra for the individual species can be extracted by assuming linear combinations of two extreme spectra.

DOI： 10.1021/jp011390u

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記述言語：英語   出版者・発行元：JAPAN SOC ANALYTICAL CHEMISTRY  

DOI： 10.2116/analsci.17.233

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

A modified generalized Born equation is incorporated with a semiempirical molecular orbital method to calculate electrostatic solvation energies for solute ions. A parameter corresponding to the atomic radius is introduced as a function of size of the solute ion and the position of the atom with respect to the solute surface. This method is applied to benzene and 17 polycyclic aromatic hydrocarbon mono-cations with various sizes and shapes in acetonitrile. The results are compared with experimental values obtained from the data of oxidation and ionization potentials. The present calculations based on the simple dielectric continuum model can predict the solvation energies with an average error of 0.07 eV. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0009-2614(99)00043-3

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DOI： 10.1016/S0009-2614(99)00277-8

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