An Atomic-Level Mechanism for Molybdenum Nitrogenase. Part 1. Reduction of Dinitrogen

Abstract

The properties of the Fe and Mo sites of the iron−molybdenum cofactor of nitrogenase with respect to binding and activation of N₂ have been studied by molecular mechanics calculations on the local protein environment and by density functional theory (DFT) calculations on subsections of the cofactor. The DFT calculations indicate that the homocitrate ligand of the cofactor can become monodentate on reduction, allowing N₂ to bind at Mo. In addition, the neighboring Fe atom plays a crucial role in N₂ reduction by stabilizing the initial reduced N₂ species and by facilitating cleavage of the N−N bond. The various possible isomers for partially reduced N₂ intermediates have been compared by DFT, and a detailed model for the reduction of N₂ is developed based on these results, together with chemical precedents and the available biochemical data for nitrogenase.