Enzymatic and catalytic reduction of dinitrogen to ammonia: Density functional theory characterization of active sites

Abstract

We used density functional calculations to model dinitrogen reduction by a FeMo cofactor containing a central nitrogen atom and by a Mo-based catalyst. Plausible intermediates, reaction pathways, and relative energetics in the enzymatic and catalytic reduction of N2 to ammonia at a single Mo center are explored. Calculations indicate that the binding of N2 to the Mo atom and the subsequent multiple protonelectron transfer to dinitrogen and its protonated species involved in the conversion of N2 are feasible energetically. In the reduction of N2 the Mo atom experiences a cycled oxidation state from Mo(IV) to Mo(VI) by nitrogenase and from Mo(III) to Mo(VI) by the molybdenum catalyst, respectively, tuning the gradual reduction of N2. Such a wide range of oxidation states exhibited by the Mo center is crucial for the gradual reduction process via successive proton-electron transfer. Present results suggest that the Mo atom in the N-centered FeMo cofactor is a likely alternative active site for dinitrogen binding and reduction under mild conditions once there is an empty site available at the Mo site. © 2005 Wiley Periodicals, Inc.