Nitric oxide transfer between nominal Fe and Co biomimetics of the nitrile hydratase active site.

Related to the inactive form of nitrile hydratase, NHase, that contains Fe(NO) within tripeptide NS binding environment, the NO transfer reactivity of (bis-mercaptoethane diazacycloheptane)Fe(NO) and (bis-mercaptoethane diazadimethylethane)Fe(NO) is compared to Co(NO) analogs. Acceptors of NO include cobalt octaethylporphyrin and the [(NS)M] dimeric precursors in the synthesis of the Fe(NO) and Co(NO) biomimetics. Qualitative rates are augmented by a definitive kinetic study finding that rates of NO transfer from (NS)M(NO) to [(NS)M'] are dependent on M and M' as well as the hydrocarbon N to N and N to S linkers. We conclude that while Fe(NO) and Co(NO) units are similar in chemical stability, minor first coordination sphere differences may favor the former, Fe(NO), consistent with the discovery of Fe(NO), but not Co(NO), in the as-isolated NHase active site.