Spectrophotometric Demonstration of Vitamin B_12S-Formation by Nucleophilic Cleavage of Co-C Bond of Acetylcobalamin

Abstract

In order to obtain further informations on the mechanism of the decomposition of the cobalt-carbon bond of acetylcobalamin by nucleophilic agents, the reaction was carried out using an appropriate apparatus under either aerobic or anaerobic conditions.
By time-course study of the spectral changes, direct spectrophotometric evidence was presented for the formation of vitamin B_12S as the initial intermediate in these reactions. Formation of acetic acid was also detected in the case of alkaline cyanidedecomposition. These facts indicate that the cleavage of the cobalt-carbon bond of acetylcobalamin by alkaline cyanide is caused by OH^- ion generated from the hydrolysis of the cyanide in a similar way as in the case of β-cyanoethylcobalamin. Discussions on the mechanism of the conversion of vitamin B_12S into dicyanocobalamin were described.