Browsing by Author "Fernández-Prini, Roberto"

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    Effect of polyelectrolytes on the kinetics of ionic reactions. Part 5.—Decomposition of 2,4-dinitrophenylphosphate in polycation solutions
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (05), 1978) Fernández-Prini, Roberto; Baumgartner, Erwin; Turyn, Daniel
    The rate of reaction of 2,4-dinitrophenylphosphate (DNPP) in solutions of added polycations has been determined in order to evaluate the influence of the polyelectrolyte effect on the rate constant. The observed enhancement of the rate of hydrolysis of DNPP by poly-(vinylbenzyltri methylammonium chloride), as well as the specific reaction of DNPP with the free amino groups of poly-(ethyleneimine) are caused by the electrostatic interactions between macroions and substrate anions. The increase in rate constants is independent of the total polyion concentration and reaches a maximum value as the ratio of polyion to substrate concentrations increases. The effect of polyions can be suppressed by addition of electrolytes. These features are characteristic of polyelectrolyte solutions to which domain models may be applied. The results obtained can be quantitatively correlated with changes produced by the macroions on the acidity constant and on the u.v. spectrum of 2,4-dinitrophenol. The role of macromolecules in facilitating the cleavage of substrates attached to more than one site of a given chain, is discussed. The relevance of these ideas to evaluation of the catalytic activity of macromolecules, e.g. enzymes, is suggested.
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    Effect of polyelectrolytes upon the kinetics of ionic reactions. Part 6.—Some general aspects
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Fernández-Prini, Roberto
    The rate constant changes of ionic reactions due to the electrostatic polyelectrolyte effect can be described in some detail. For second-order reactions between ions of equal charge sign, it is shown that the inhomogeneous distribution of reactive ions is equivalent to a primary salt effect; the primary salt effect cannot explain the results at high macroion concentration. An expression is derived for this case taking into account the probability of site occupancy by both reactive partners. For first-order reactions, the overall change in rate constant with polymer concentration may be explained in terms of the theories of polyelectrolyte solutions, even when the electrostatic effect may be coupled with more specific interactions.