We demonstrate electrochemical control of the nitrogenase MoFe protein, in the absence of Fe protein or ATP, using europium( iii/ ii) polyaminocarboxylate complexes as electron transfer mediators. This allows the potential dependence of proton reduction and inhibitor (CO) binding to the active site FeMo-cofactor to be established. Reduction of protons to H 2 is catalyzed by the wild type MoFe protein and β-98 Tyr→His and β-99 Phe→His variants of the MoFe protein at potentials more negative than –800 mV ( vs. SHE), with greater electrocatalytic proton reduction rates observed for the variants compared to the wild type protein. Electrocatalytic proton reduction is strongly attenuated by carbon monoxide (CO), and the potential-dependence of CO binding to the FeMo-cofactor is determined by in situ infrared (IR) spectroelectrochemistry. The vibrational wavenumbers for CO coordinated to the FeMo-cofactor are consistent with earlier IR studies on the MoFe protein with Fe protein/ATP as reductant showing that electrochemically generated states of the protein are closely related to states generated with the native Fe protein as electron donor.
†Electronic supplementary information (ESI) available: Further details of experimental methods, diagram and description of the electrochemical cell, proton reduction assay data, electrochemical data from control experiments on the Eu–L complexes alone, and a comparison of the current arising from wild type MoFe protein under N 2 and Ar. See DOI: 10.1039/c6sc02860h