Metal-ion assisted catalysis of nucleophilic attack. Part 3. Co-operation between metal ion and hydroxide

Abstract

A rapid path for the hydration of acetaldehyde is demonstrated, in which a zinc complex and the hydroxide ion co-operate as catalysts. In the mechanism proposed a zinc-bound hydroxide ion attacks directly the carbonyl group of the aldehyde. Comparison of the nucleophilic strengths of hydroxide ions in various complexes demonstrates a correlation similar to that obtained by other workers for attack on propionic anhydride and on carbon dioxide. The enzyme carbonic anhydrase behaves consistently with this correlation for the substrate acetaldehyde, but not for the substrate carbon dioxide.