-Yang Wen

Ion-solvent interaction. Structural aspects of ion-solvent interaction in aqueous solutions: a suggested picture of water structure

Abstract : In addition to the direct action of the ionic charge on water as a dielectric medium, ions may exert an influence on the equilibrium between the ice-like and non-ice-like forms which are present in room-temperature water. This provides a way of accounting for experimental results in a variety of areas, including entropy, heat capacity, temperature of maximum density, tracer selfdiffusion, thermal conductivity, and dielectric relaxation, as well as viscosity and ionic mobility and their temperature coefficients. The tetrabutyl ammonium cation acts as a structure-promoter in the same way as do non-polar solutes, amino acids and fatty acid anions. These various effects seem explicable in a straightforward manner in terms of a new picture of water as consisting of flickering clusters of hydrogen-bonded molecules, in which the cooperative nature of cluster formation and relaxation is related to the partially covalent character which is postulated for the hydrogen bond. (Author)

Structural Aspects of Aqueous Tetraalkylammonium Salt Solutions

Various thermodynamic and spectroscopic investigations on aqueous tetraalkylammonium salt solutions are reviewed from a structural viewpoint. At present, it is not yet clear what kind of water structure is formed around the alkyl groups of the large cations. However, the importance of “cosphere” overlap and ion-ion interaction (cation-anion, cation-cation, cation-anion-cation, etc.) in determining the solution properties are emerging more clearly. In this regard, model calculations based on the approach of Friedman and his coworkers are expected to be of considerable value.

Thermodynamics of some perfluorocarbon gases in water

The solubilities of CF4 and C2F6 gases in H2O and D2O in the temperature range of 5 to 30°C at 5° intervals and C3F8 and c-C4F8 gases in H2O over the temperature ranges of 5 to 15°C and 5 to 30°C, respectively, have been determined. From the solubility data various thermodynamic quantities for the process of dissolution have been derived. These data were compared with our results of applying the scaled-particle theory to gain an insight into the various thermodynamic processes accompanying the gas dissolution. One of our conclusions is that the “hydrophobicity” of the perfluorocarbons is greater than that of the corresponding alkanes.

Chemical shifts of aqueous nonelectrolyte solutions: Influence of the polar and nonpolar groups on the water proton shifts at 0C

Hydroxyl-proton chemical shifts of alcohol mixtures and aqueous solutions containing some nonelectrolytes (alcohols, ketones, cyclic ethers, and amines) have been measured at 60 MHz and at 0°C. Methyl-proton resonance of the solutes was used as the internal reference and the water-proton shifts in solutions were measured with respect to pure water. Downfield shifts for some alcohols (particularly tertiary butanol and iso-propanol), cyclic ethers, and amines in the water-rich region were confirmed For alcohols and some other nonelectrolytes in water, the observed shifts were decomposed to component contributions arising from the “polar group” effect, “solute proton” effect, and “nonpolar group” effect. Polar effects are found to contribute a substantial fraction of the observed downfield shifts. After subtracting these polar contributions, however, there still remains certain amounts of downfield shifts which may be attributed to the effect of nonpolar groups on the water structure. The downfield shifts are found to be relatively large when the solutes have branched alkyl groups with nearly spherical shape and with diameters of about 5 Å. Strikingly large downfield shifts of water proton resonance were found for some secondary amines and tertiary diamines with globular shape. However, in view of the extrapolation technique employed in evaluating the “polar group” effect, the downfield “nonpolar group” effect we estimated should be considered as the upper limits.

Solubilities of hydrogen and deuterium gases in water and their isotope fractionation factor

AbstractSolubilities of deuterium gas in water were measured at 5° intervals from 278 to 303°K with an overall precision of about 0.4%. Thermodynamic functions for the solution process were calculated for deuterium gas and compared with the corresponding quantities for hydrogen gas based on the reported data of Crozier and Yamamoto. Henrys law constantsk, obtained at different temperaturesT, were fitted to an equation of the form

Solubility of methane in aqueous solutions of triethylenediamine

R ln ({1 \mathord{\left/ {\vphantom {1 k}} \right. \kern-\nulldelimiterspace} k}) = A + {B \mathord{\left/ {\vphantom {B {T + }}} \right. \kern-\nulldelimiterspace} {T + }}C ln T + DT

Measurement of Diffusion Coefficients in Polystyrene Using Xenon-129 NMR

Isotope fractionation factors α for the D2/H2 system were obtained with careful error estimates. Compared at the same temperature, D2 gas is more soluble in water than H2 gas, showing a “normal” isotope effect, and the value of α decreases from 1.086 (±0.005) at 278°K to 1.065 (±0.006) at 303°K. The large isotope effect may be attributed, at least partly, to the difference in the zero-point energies between H2 and D2 molecules when they execute oscillatory motion in a solvent cage.

Viscosity and apparent molal volumes of aqueous triethylenediamine

Recalculations of the Gurney free-energy parameters Aij based on the cosphereoverlap model of Friedman and co-workers have been made using more recent experimental data. Our procedure for calculation seems to be more systematic than those previously reported. The excess energy, entropy, and volume parameters (Eij, TSij, and Vij) were also recalculated for some aqueous tetraalkylammonium halides. In addition, the excess-heat-capacity parameters Cij are also reported here for the first time. These data are discussed briefly in terms of the structural implications.