Electroenzymatic Nitrogen Fixation Using an Organic Redox Polymer-Immobilized MoFe Protein System.

Nitrogenase is the only biological catalyst that is known to convert dinitrogen (N2) to ammonia (NH3). Nitrogenase-catalyzed NH3 formation in vivo is energetically intensive due to a series of events, including a Fe protein cycle coupled with ATP hydrolysis. Furthermore, the complexity of nitrogenase's cofactors plagues related bioelec-trodes by unstable and poor electric wiring between the cofactors and the electrode, thereby lowering the overall bioelectrocatalytic perfor-mance. We report an organic redox polymer-based electroenzymatic nitrogen fixation system using a metal-free redox polymer namely neutral red-modified poly(glycidyl methacrylate-co-methylmethacry-late-co-poly(ethyleneglycol)methacrylate) with a low redox potential of -0.58 V vs. SCE. The stable and efficient electric wiring of nitrogenase within the redox polymer matrix enables mediated bioelectrocatalysis of N3-, NO2- and N2 to NH3 catalyzed by the MoFe protein via the polymer-bound redox moieties distributed in the polymer matrix in the absence of the Fe protein. Bulk bioelectrosynthetic experiments pro-duced 209 ± 30 nmol NH3 nmol MoFe-1 h-1 from N2 reduction. 15N2 labeling experiments and NMR analysis were performed to confirm biosynthetic N2 reduction to NH3.