pH Dependent Mechanisms of Hydrolysis of 4-Nitrophenyl β-D-Glucoside

Abstract

1,2-trans-Glycosides hydrolyze through a range of mechanisms under conditions of different pH, but systematic studies are lacking. Here we report the pH-rate constant profile for the hydrolysis of 4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect (k(H3O+)/k(D3O+) = 0.63) in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region exhibited general catalysis with a single proton in flight with a normal solvent isotope effect of kH/kD = 1.5, and when extrapolated to zero buffer concentration show a small solve..