Resonance Raman spectra of vitamin B12 and some cobalt corrinoid derivatives

Abstract

Resonance Raman spectra in the frequency region 200–3200 cm^–1 are reported for very dilute aqueous solutions of the following compounds: cyanocobalamin (vitamin B₁₂), aquocobalamin (B_12a), hydroxocobalamin (B_12b), dicyanocobinamide, the alkaline hydrolysis products of B₁₂(penta- and hexa-carboxylate derivatives), aquocobalamin (B_12r), and {cobalamin}–cobalt(I)(B_12s). The spectra were excited by lines from an argon laser, selected so as to coincide with bands in the visible absorption spectra of the compounds, and to satisfy the conditions for rigorous resonance enhancement of selected vibrational band intensities. The Co^III compounds all gave closely similar spectra, with no major changes being induced by coordination displacement even of the large 5,6-dimethylbenzimidazole base group from the metal. However, large changes in the structure of the spectra resulted from reduction of B₁₂ to B_12r and B_12s; these changes appear to be related to conformational changes in the corrin ring chromophor.