A self-assembled supramolecular host catalyzes the hydrolysis of acetals in basic aqueous solution. The mechanism of hydrolysis is consistent with the Michaelis− Menten kinetic model. Further investigation of the rate-limiting step of the reaction revealed a negative entropy of activation (Δ S⧧=− 9 cal mol− 1 K− 1) and an inverse solvent isotope effect (k (H2O)/k (D2O)= 0.62). These data suggest that the mechanism of hydrolysis that takes ...