Catalytic Reduction of Acetylene with Participation of Isolated FeMo-co from Azotobacter vinelandii in Non-Enzymatic Conditions

Abstract

We have been studying the reactions of the isolated iron-molybdenum cofactor nitrogenase with acetylene. FeMo-co from Azotobacter vinelandii has been isolated from the MoFe protein as published (McLean, et al. 1989). The reaction with C₂H₂ was carried out in DMF because FeMo-co survives in this solvent without destruction for a long time in the absence of water and oxygen. We found that it was an effective catalyst for acetylene reduction by zinc amalgam (Bazhenova et al., 1997). Cyclic voltammetry of FeMo-co in DMF solution showed a quasi-reversible reduction apparently to the substrate reducing state with a cathodic wave potential of − 0.73 V vs. NHE (Strelets, V.V., personal communication). For zinc amalgam, an E _o (Zn²⁺/Zn(Hg)) in DMF in the presence of PhSH of − 0.84 V vs. NHE was measured. Thiophenol was a source of protons and an important cocatalyst. It stabilizes the system and the reaction rate does not change for several hours. We found that the reaction proceeds on the amalgam surface. Apparently thiophenol increases the adsorption ability of FeMo-co and acts as an electron conductive bridge between the multi-electron reductant and the catalyst (Bazhenova, et al., unpublished).