151. Density Functional Theory Calculations and Exploration of a Possible Mechanism of N2 Reduction by Nitrogenase.
- Author
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Uwe Huniar, Ahlrichs, Reinhart, and Coucouvanis, Dimitri
- Subjects
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CHEMICAL reduction , *NITROGENASES , *OXIDOREDUCTASES , *GLYCOLS , *CATALYSIS , *PHYSICAL & theoretical chemistry - Abstract
Density functional theory (DFT) calculations have been performed on the nitrogenase cofactor, FeMoco. Issues that have been addressed concern the nature of M-M interactions and the identity and origin of the central light atom, revealed in a recent crystallographic study of the FeMo protein of nitrogenase (Einsle, O.; et al. Science 2002, 297, 871). Introduction of Se in place of the S atoms in the cofactor and energy minimization results in an optimized structure very similar to that in the native enzyme. The nearly identical, short, lengths of the Fe-Fe distances in the Se and S analogues are interpreted in terms of M-M weak bonding interactions. DFT calculations with O or N as the central atoms in the FeMoco marginally support the assignment of the central atom as N rather than O. The assumption was made that the central atom is the N atom, and steps of a catalytic cycle were calculated starting with either of two possible states for the cofactor and maintaining the same charge throughout (by addition of equal numbers of H+ and e-) between steps. The states were [(CI)FeII 6FeIII MOIVS9(H+)3N3-(GI)(Im)]2-, [I-N-3H]2-, and ((Cl)FeII 4FeIII 3- MoIVS9(H+)3N3(GI)(Im)], [I-N-3H]0 (GI = deprotonated glycol; Im = imidazole). These are the triply protonated ENDOR/ESEEM [I-N]5- and Mõssbauer [I-N]3- models, respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2004
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