Remarkably efficient hydrolysis of a 4-nitrophenyl ester by a catalytic antibody raised to an ammonium hapten

Abstract

Antibodies have been raised to a 1-benzazepine hapten and the properties of two of the strongly binding clones, designated C3 and C5, as catalysts examined. Neither antibody catalysed the reaction for which they were first generated, electrophilic substitution in the benzene ring, but C3 catalysed the hydrolysis of an aralkyl 4-nitrophenyl ester with a rate enhancement of more than 10⁶ compared with the background solvolysis rate. The mechanism of the hydrolysis reaction is suggested to involve general base catalysis on the basis of chemical modification experiments and isotope effects on the reaction rate in D₂O. The possibility that C3 might catalyse other reactions (elimination, deuterium exchange, and epoxide opening) was investigated but no other reactions were observed. In contrast, C5 catalysed none of the reactions investigated. The properties of the two antibodies are discussed with respect to their ability to bind compounds structurally related to the hapten.