Spacer-Assisted Catalytic Action of Imidazole-Appended γ-Cyclodextrin

This is the authors' abstract. We don't add key points for this paper.

Catalytic activity of γ-cyclodextrin bearing an imidazole moiety (1) was compared with that of the corresponding β-cyclodextrin derivative (2) in the hydrolysis of p-nitrophenyl acetate. The catalysts 1 and 2 hydrolyzed the ester 80 and 172 times, respectively, as fast in the complexes as the buffer without any catalyst. The binding of 1 for the ester was 40% weaker than that of 2. When sodium 1-naphthaleneacetate was present in the catalytic systems, the hydrolysis rate was enhanced for 1, but depressed for 2. This rate enhancement of 1 suggests that sodium 1-naphthaleneacetate acts as a spacer which facilitates 1 to bind the substrate by narrowing the large γ-cyclodextrin cavity. The time dependency of p-nitrophenol formation under the conditions of large excess of p-nitrophenyl acetate to 1 or 2 exhibited that the inhibitory effect of the product was remarkable for 2, but negligible for 1.