The effect of increasing the hydrophobicity of penicillin on its micelle-catalysed hydrolysis

Abstract

Micelles of cetyltrimethylammonium bromide catalyse the alkaline hydrolysis of alkylpenicillins and benzylpenicillin methyl ester, The equilibrium constant for binding the alkylpenicillin to the micelle and the rate constants have been obtained. Binding increases with increasing alkyl chain length but shows a non-linear dependence upon the Hansch π-value and the rate reaches a maximum value with heptylpenicillin. The free energy of transfer of a methylene group from water to the micelle shows a maximum value of 0.71 kcal mol^–1. The negative charge of the carboxytate group of penicillin is not necessary tor catalysis.