Browsing by Author "Baumgartner, Erwin"

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    Change of Apparent Acidity Constant of Indicators in Polyelectrolyte Solutions
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (08), 1974) Baumgartner, Erwin; FernAndez-Prini, Roberto; Turyn, Daniel
    The change of apparent pK and visible spectra of pH indicators produced by polyeleclrolytcs has been studied. Appreciable changes are observed when indicators have opposite charge to that of the polyions. The effect of polyelectrolyte concentration, molecular weight of the macroions, and addition of simple salts and dioxan to the solutions are reported. The observed phenomena may be attributed to the “ polyelectrolyte effect ” due to the large charge density on the polymeric chains. There are however non-electrostatic interactions contributing to the changes in indicator properties; stacking of dye molecules may be ruled out. The relevance of these studies in the field of ionic reactions in the presence of macroions and their relationship with the so called protein error, introduced in colorimetric pH determinations by the presence of proteins or colloids, is discussed.
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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.