Effect of polyelectrolytes on the kinetics of ionic reactions. Part 2.—Decomposition of p-nitrophenyl phosphate in aqueous solutions of polycations

Abstract

The decomposition of p-nitrophenyl phosphate in solutions containing polyethyleneimine (PEI) or poly(benzyltrimethylammonium chloride)(PVBA-Cl) has been studied. The polyelectrolytes markedly affect the rate of substrate decomposition. PVBA-Cl catalyses the hydrolysis of the substrate at pH > 6 because the substrate/PVBA-Cl interactions facilitate ester bond cleavage. In PEI solutions nucleophilic attack by the free amino groups of the macroion leads to production of substituted p-nitroaniline (pH > 6). The effects of polyelectrolyte concentration and molecular weight are discussed.

All the observed changes in the rate of substrate decomposition originate in the electrostatic field of the polyions. When the charge of the macroions is reduced by added salts or by changing the degree of ionization of the polymeric chains, the observed polyelectrolyte effect tends to disappear. An electrostatic model based on polyionic domains satisfactorily explains the rate constants observed in PEI solutions.