The Chatt cycle and the mechanism of enzymic reduction of molecular nitrogen

The Chatt Cycle is a hypothetical model for the mechanism of nitrogenase action at the atomic level and is based upon reactions of certain well-defined molybdenum compounds. The proton and electron-transfer chemistry of the cycle is reviewed, revised and extended. An explanation for general and obligatory hydrogen evolution by the nitrogenase system is advanced; this involves carboxylate acting as a tethered leaving group at the Mo centre and the formation of mono-, di- and tri-hydric intermediates. The chemical model is integrated with the biochemical model proposed by Lowe and Thorneley.