Author ORCID Identifier

Mark R. Chance

Document Type


Publication Date



Examination of the role of base-off cobalamin species (where the 5,6-dimethylbenzimidazole ligand coordinated to cobalt is detached by protonation of the imidazole nitrogen) in differentiation between homolytic and heterolytic cobalt-carbon bond cleavage mechanisms is a primary step in better understanding B12-dependent enzyme catalysis. X-ray absorption edge spectroscopy provides the first direct structural evidence of five-coordination in base-off adenosyl- and base-off methylcobalamin complexes at room temperature. Integration of 1s-3d pre-edge transitions of the base-off species reveals the dependence of coordination number on temperature. Gradual increases in 1s-3d transition intensities, as the temperature is increased from 180 K to 298 K, reflect a change in the coordination number from six (where a water molecule is presumed to occupy the coordination site vacated by the 5,6-dimethylbenzimidazole ligand) to primarily five-coordinate. Base-off configurations that strengthen the CoC bond may be both decreasing the tendency for homolytic cleavage while increasing the tendency for hetrolytic Co(I) B12 formation.

Publication Title

Journal of Inorganic Biochemistry





First Page


Last Page



10.1016/0162-0134(93)80062-E" data-hide-no-mentions="true">
10.1016/0162-0134(93)80062-E" data-hide-zero-citations="true" data-style="small_circle">

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