Multifunctional Hydrolytic Catalyses. 8. Remarkable Acceleration of the Hydrolysis of p-Nitrophenyl Acetate by Micellar Bifunctional Catalysts

Surfactant molecules which contain the hydroxamate and imidazole functions were synthesized, and their catalytic actions in aqueous cetyltrimethylammonium bromide micelles were examined for the hydrolysis of p-nitrophenyl acetate at 30 °C. The catalysis proceeded mainly via acylation and imidazole-catalyzed deacylation at the hydroxamate group. Both of these processes were remarkably accelerated in the case of bifunctional micelles, due to activation of anionic nucleophiles in cationic micellar environments. The overall catalytic efficiency exceeded even that of α-chymotrypsin at pH 8 and was more than 5000 times higher than that of imidazole. Micellar monofunctional catalysts and a nonmicellar bifunctional catalyst were much less effective. Therefore, the combination of bifunctionality and micellar microenvironments was essential for the highly efficient catalysis.