Hydrolytic Enzyme Models

Polycarboxylic acids containing a small number of p-nitrophenyl ester or p-nitroanilide groups were prepared and the pH dependence of their hydrolysis rates was investigated. The ester hydrolysis was found to be strongly catalyzed by an ionized carboxyl attached to the γ-carbon, resulting in an acceleration of the hydrolysis rate by a factor of about 106 at pH 5–6. The hydrolysis of p-nitroanilide groups was apparently affected little by one carboxylate in the γ position, but it was effectively inhibited when the carboxyls attached to both γ-carbons were ionized.