PHOTOLYSIS OF METHYLCOBALAMIN - NATURE OF THE REACTIVE EXCITED-STATE

Photolysis of methylcobalamin (Co(III)corrin(CH3)L + H2O + O2 --> Co(I II)(H2O)L + H2CO + OH-) shows a pronounced wave-length dependence. It is suggested that the reactive excited state is of the ligand-to-ligan d charge transfer (LLCT) type and involves the promotion of an electro n from the Co-C sigma-bond to a pi(corrin) orbital. This LLCT transit ion mixes with the pipi(corrin) transitions. Owing to this LLCT contr ibution, the pipi-absorption bands are also photoactive but with redu ced efficiency.