The study, by ESR and quantum chemistry, of the fundamental process of cobalt to carbon homolytic bond cleavage in Adenosylcobalamin and related model compounds. Our primary experimental goals are to detect and analyze accurately the line shapes characteristic of weakly spin-spin coupled Co(II)alamine...free radical pairs using both 9 GHz and 35 GHz ESR spectroscopy. Our primary theoretical goals are to model the singlet-triplet energy splitting versus distance, and relate these calculations to both ESR and other known chemical and biochemical properties related to activation and cleave of the Co-C bond. Our ultimate goal is a detailed molecular picture of AdoCbl activation/deactivation as a result of protein/substrate/allosteric modifier molecular events.