Vanadium nitrogenase cubane clusters

Zuo, J.L., H.C. Zhou, and R.H. Holm. 2003. Vanadium-iron-sulfur clusters containing the cubane-type [VFejSJ core unit Synthesis of a cluster with the topology of the PN cluster of nitrogenase. Inorg. Chem. 42 4624—4631. 

All of these beautiful model complexes for nitrogen fixation have one disadvantage in common they do not represent any of the structural features of the iron-vanadium cofactor in the nitrogenase. In contrast, cubane clusters constimting the vanadium-iron-sulfur moiety of the FeMoco are expedient structural models, with the disadvantage, however, that they do not catalyse the reduction of N2. 

The model compounds do not bind or reduce N2 or other nitrogenase However, some iron-vanadium-sulfur clusters will reduce hydrazine to ammonia. In a systematic evaluation of the metal M in double cubane clusters [M2Fe6Sg(SEt)9] (M = V, Nb, Mo, W, Re), it was found that the reduction potential is lower, and the Fe Mossbauer isomer shift higher, for Mo relative to However, the Fe isomer shifts are similar between MoFe and VFe proteins, suggesting that protein interactions (especially hydrogen bonding) are likely to play an important role in determining the electron density at the iron atoms in the FeMoco and... 

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