Dr. Ragnar Björnsson, Science Institute, University of Iceland, presents:
Nitrogenase is an enzyme that catalyzes the formation of ammonia through the reduction of molecular nitrogen through an unknown mechanism. The molecular structure of the complex iron-molybdenum cofactor (FeMoco) was only recently fully characterized with the identification of the carbide in the center of the cluster. However, important prerequisites for understanding the reaction mechanism - the total charge, metal oxidation states and electronic structure have not been fully clarified.
Here we present the results of a joint experimental-theoretical study of the FeMo cofactor of nitrogenase. Mo X-ray absorption spectroscopy combined with TDDFT-computed spectra of nitrogenase MoFe protein as well as synthetic MoFe3S4 model complexes was used to directly gain insight into the electronic structure in this complex metal-sulfur cluster.
The results give evidence for a revised oxidation state of the molybdenum atom that is supported by broken-symmetry DFT calculations. The implications for this new assignment are discussed, particularly the forgotten connection between the cofactor and catalytically active synthetic model compounds. Future research directions of the group are presented.