Electronic structure and bonding in vitamin B12, cyanocobalamin

The electronic structure of the vitamin B-12 molecule, cyanocobalamin, is calculated by a first-principles method, which provides an interpretation of the optical absorption data and is consistent with soft X-ray fluorescence measurements. A fixed accurately determined geometry was used for the calculation. The large difference in the HOMO-LUMO gap compared to existing calculations, using only the analogous corrin derivative, is evidence that the side chains (particularly the nucleotide loop) strongly influence the electronic structure. (C) 2003 Elsevier Science B.V. All rights reserved.