Unique peculiarities of the structure of the Fe-Mo cofactor of nitrogenase favorable for multicenter coordination of a nitrogen molecule

Abstract

The probable coordination mode of a nitrogen molecule on the Fe-Mo cofactor of nitrogenase has been theoretically considered, taking into account both the well-known data on the structure of the Fe-Mo cofactor and the substrate selectivity of nitrogenase and the results of semiempirical calculations of the electronic structures of the cofactor and its complexes with molecular nitrogen. The distances between the Fe atoms in the cofactor are favorable for different multicenter coordination modes of a nitrogen molecule: above the Fe4 face along its diagonal, through this face, and inside the Fe6 prism perpendicularly to its axes. It is important that the nitrogen atoms are open for protonation in all coordination modes. The first mode is disadvantageous due to steric hindrances. Of the other variants, the latter is the most favorable both energetically and from the viewpoint of weakening of the N-N bond.