Abstract:
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.
