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Subject: search.filters.subject.Preferential Solvation

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    D2O-H2O Isotope Effect on Nuclear Magnetic Relaxation of Alkali Halide Nuclei and Preferential Solvation in Mixed Solvents
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (3), 1978) Holz, Manfred
    The effect of substitution of H2O by D2O on the nuclear magnetic relaxation of the ionic nuclei 23Na, 87Rb and 81Br, which all relax by quadrupole interaction, has been investigated in several NaBr and RbBr solutions. The solvents were neat water and binary mixtures of water with methanol, formamide and dimethylsulphoxide. In the neat aqueous solutions it was found experimentally that the isotope effect is similar to that on the viscosity and that even at high salt concentrations, where all water is “hydration water”, this effect is still relatively strong. In the mixed solvents the composition dependence of the isotope effect on the relaxation rates has been studied in the water rich region, showing e.g. in methanol + water mixtures a quite different behaviour for cationic and anionic nuclei. A new method is presented, which, with certain assumptions, allows us to calculate the local mole fraction of water in the inner solvation sphere of the ions from the measured D2O–H2O isotope effect as a function of the macroscopic solvent composition. The analysis yielded the result that Na+ and Rb+ in methanol + water and to a smaller extent also Rb+ in formamide + water are preferentially hydrated. In the same way it was found that Br– is weakly preferentially solvated by methanol and Na+ by dimethylsulphoxide, whereas Br– is not selectively solvated in formamide + water. The results are discussed and compared with those obtained by other methods.
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    Nuclear magnetic resonance studies of preferential solvation: Part 4.—Thermodynamic treatment involving non-statistical distribution of solvated species
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (10), 1974) Covington, Arthur K.; Thain, Jennifer M.
    The solvation of an ion in a binary solvent mixture has been treated in terms of consecutive stepwise equilibria with the solvent exchange process becoming more, or less, energetically favourable as the solvation shell becomes successively richer in the second component. Equations developed can be used to fit a wide range of observed n.m.r. chemical, and u.v. peak maximum, shift results in mixed solvents, such as dimethyl sulphoxide + H2O, acetonitrile + H2O, ethylenediamine + water. A classification of the observed behaviour is presented in terms of two parameters, K1/n(K1/n > 1 preferential solvation by second component, where n is the solvation number) and k(1.5 > k > 0.5). It is concluded that Cs+, NO–3, I– are preferentially solvated by DMSO and Li+ slightly preferentially solvated by H2O, in DMSO + H2O mixtures. In acetonitrile + H2O mixtures, Na+, Cl–, Br–, I– are preferentially hydrated.
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    Nuclear magnetic resonance studies of preferential solvation: Part 3.—Thermodynamic treatment involving change of solvation number, and application to dimethyl sulphoxide-containing solvents
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (10), 1974) Covington, Arthur K.; Lantzke, Ian R.; Thain, Jennifer M.
    Studies of 7Li and 133Cs ion n.m.r. chemical shifts in dimethyl sulphoxide (DMSO)+ water mixtures, have been interpreted in terms of a series of competitive equilibria in which the solvation number of the ions for DMSO is half that for water. It is concluded that nitrate ions are preferentially solvated by DMSO and Li+ by water. The treatment has also been applied to 133Cs shift data for sulpholan and water mixtures, and it is concluded that caesium ions are solvated by the organic component.