BIFUNCTIONAL ACID-BASE CATALYSIS BY IMIDAZOLE GROUPS IN ENZYME MIMICS

The cleavage of RNA can be catalyzed by imidazole buffer, and shows sequential bifunctional catalysis. When the two imidazole groups are attached to the same catalyst, as in enzymes or in cyclodextrin bis-imidazole derivatives, simultaneous bifunctional catalysis is seen. The geometric preference for such bifunctional catalysis is revealed by the use of three isomeric cyclodextrin bis-imidazoles. Different isomers are preferred for phosphate ester hydrolysis and for ketone enolization, and the preferences reveal details of the catalytic mechanisms.