Multifunctional hydrolytic catalyses x. Catalytic hydrolysis of p-Nitrophenyl acetate by a polyethylenimine derivative containing hydroxamate (Zwitterionic) group

A water-soluble polyethylenimine derivatives was prepared containing the zwittenionic hydroxamate group, 11 mol% dococyl side chain, and a tertiary amino group. This polymer hydrolyzes p-nitrophenyl esters very effeciently (30°C, 3 v/v% EtOHH₂O), according to the Michaelis-Menten kinetics. The catalysis involves substrate binding (K_m= (2-5) × 10^-4M in the case of p-nitrophenyl acetate) due to hydrophobic interaction, and facile acylation and de-acylation at the hydroxamate site. The zwitterionic nature and the hydrophobic microenvironment contribute to the enchanced nucleophilicity to the hydroxamate group. It is suggested that the de-acylation process involves general-base catalysis by the tert-amino group. The overall catalytic effeciency for p-nitrophenyl acetate exceeded that of α-chymotrypsin by a factor of ca. 100 under a comparable condition. Polymers which do not contain the hydroxamate group or contain the imidazole group in its place were much less effective.