Incorporation of an Asymmetric Mo-Fe-S Cluster as an Artificial Cofactor into Nitrogenase.

Nitrogenase employs a sophisticated electron transfer system and a Mo-Fe-S-C cofactor, designated the M-cluster [(cit)MoFe 7 S 9 C]), to reduce atmospheric N 2 to bioaccessible NH 3 . Previously, we have shown that the cofactor-free form of nitrogenase can be repurposed as a protein scaffold for the incorporation of a synthetic Fe-S cluster [Fe 6 S 9 (SEt) 2 ] 4- . Here, we demonstrate the utility of an asymmetric Mo-Fe-S cluster [Cp*MoFe 5 S 9 (SH)] 3- as an alternative artificial cofactor upon incorporation into the cofactor-free nitrogenase scaffold. The resultant semi-artificial enzyme catalytically reduces C 2 H 2 to C 2 H 4 , and CN - into short-chain hydrocarbons, yet it is clearly distinct in activity from its [Fe 6 S 9 (SEt) 2 ] 4- -reconstituted counterpart, pointing to the possibility to employ molecular design and cluster synthesis strategies to further develop semi-artificial or artificial systems with desired catalytic activities.