• Xing-Ya Li

      Articles written in Journal of Chemical Sciences

    • The effect of hydrophobic-lipophilic interactions on chemical reactivity. 9. Putting the spotlight on lipophilic forces in solvent-effect studies

      Xi-Kui Jiang Xing-Ya Li Bang-Zhou Huang

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      The hydrolytic rate constants of thep-nitrophenyl esters of acetic, octanoic, dodecanoic and hexadecanoic acids in six aquiorgano binary mixtures of graded compositions at various initial substrate concentrations were measured and discussed in terms of the hydrophobic-lipophilic interactions between the substrate molecules, and the organic cosolvents which were MeOH, Me2SO, 1, 4-dioxane, 1,2-dimethoxyethane,n-propanol andt-butanol. The accelerating or retarding effects of the organic cosolvents on the rate constants of hydrolysis were found to be directly related to the lipophilicities of the solvents which were changed either by changing the content (ϕ) or the nature of the organic cosolvent. The classification or ordering of the six solvents on the basis of their solvent effects were found to conform to the lipophilicity order derived from Rekker's Σf values. The results support the proposition that lipophilic interactions can play an important role in solvent effects of aqueous binaries.

    • The effect of hydrophobic-lipophilic interactions on chemical reactivity. 10. The competition between the aggregation of long-chain esters and the formation of inclusion complexes of these esters with amylose

      Xi-Kui Jiang Xing-Ya Li Bang-Zhou Huang

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      The hydrolytic pseudo-first-order rate constants (kad) ofp-nitrophenyl esters of dodecanoic acid (C12) and hexadecanoic acid (C16) at different initial substrate concentrations ([S]i) in the six aquiorgano binary mixtures of different compositions (ϕ) were measured. These rate constants (kad) were compared with the corresponding rate constants obtained in the absence of sodium carboxymethylamylose (Na-CMA) (kun) in order to study the competition between the formation of inclusion complexes of these esters with Na-CMA and the aggregation of these long-chain substrates. Values of ΔCAgC andkad/kun were compiled and their significance discussed on the basis of a postulated two-path mechanism. Our results suggest that in addition to path A which involves encapsulation by Na-CMA of the monomeric C12 or C16 only, there is a second path (path B). Path B describes a process in which Na-CMA breaks up aggregates of all sizes into smaller ones as well as monomeric species which can be wrapped-up by Na-CMA simultaneously or subsequently.

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