Dalton Transactions Blog

In this HOT article, Ian Dance examines afresh the relationships between CO and H on nitrogenase cofactors following the recent finding that vanadium nitrogenase and modified molybdenum nitrogenase reduce CO to hydrocarbons. In order to assist the interpretation of kinetic infrared spectral data, vibrational frequencies and modes have been calculated for a variety of possible structures in which FeMo-co bears H atoms, or CO ligands, or both.

Fe–H stretching frequencies occur in the same spectral window as the C–O stretching frequencies, with lesser intensity, and both stretches are strongly coupled in some structures. Symmetrical bridging of CO between two Fe atoms of FeMo-co is destabilised by the presence of other ligands on Fe, and the reason for this is evident. Two results for bound formyl, HCO, are reported. These calculations of reference structures allow some interpretation of existing experimental spectra, but, perhaps more significantly, they suggest further kinetic infrared experiments to elucidate the chemical mechanism of catalysis by nitrogenase under normal turnover conditions.

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Calculated vibrational frequencies for FeMo-co, the active site of nitrogenase, bearing hydrogen atoms and carbon monoxide
Ian Dance
Dalton Trans., 2011, Advance Article
DOI: 10.1039/C1DT10505