Water-soluble bifunctional polymers which contained N-phenylacrylohydroxamate unit and 4(5)-vinylimidazole unit were prepared, and the catalytic hydrolysis of p-nitrophenyl acetate was studied at 30°C in 28.9% EtOH-H2O. Under ordinary substrate concentrations (10-4-10-5M), the reaction followed the simple firstorder kinetics, indicating the complete turnover of the catalytic group. At higher substrate concentrations, the time course of the reaction was biphasic and the hydrolysis was shown to proceed mainly via the formation and the subsequent decomposition of the acetyl hydroxamate intermediate. The acylation rate at the hydroxamate anion unit was affected only insignificantly by the presence of the imidazole unit, and was much more efficient than those at the imidazole site. In contrast, the decomposition of the acetyl intermediate was remarkably accelerated (up to 103-fold) by the introduction of the imidazole unit. Thus, the appropriate combination of the nucleophilic functions of complementary nature led to much enhanced turnover rates of the catalytic site.
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