Nitrogenase : a unique iron-molybdenum cluster for nitrogen activation

Without doubt, the most complex biological clusters are found in nitrogenase, the enzyme that fixes nitrogen from the air and converts it into ammonia, a reaction of vital importance to plants (nitrogen cycle) and one that has fascinated chemists for a very long time. To catalyze this reduction reaction, nature has chosen two iron- and sulfur-based clusters: the P cluster, made up of eight iron atoms and seven sulfur atoms, which is essentially involved in transferring electrons to the second cluster, and the Fe-Moco cluster, made up of seven iron atoms, one molybdenum atom, one carbon atom and nine sulfur atoms, which is the site of _N2 fixation and its multi-electron reduction. The structure of nitrogenase, its clusters and currently accepted mechanistic hypotheses are presented in this lecture. This work has long been complemented by bio-inspired chemistry approaches, which involve synthesizing small mono- or polynuclear iron and/or molybdenum complexes and assessing their nitrogen reduction capacity. Recent results are also discussed. Finally, we present the complex multi-protein biosynthesis systems of nitrogenase clusters and their mode of action.