DFT analysis of the active site in catalytic metabolic redox reactions of mononuclear molybdenum enzymes

Abstract

Model complexes [Mo^VIO₂(S₂C₂Me₂)SMe]⁻ (A, derived from the X-ray crystal structure of native sulfite oxidase (SO)) and [Mo^VIO₂(mnt)₂]²⁻ (B, coordination mode similar to the active site of selenate reductase (SeR)) were computed at the COSMO-B3LYP/SDDp//B3LYP/Lanl2DZ(p) energy level of Density Functional Theory in order to study their behavior in oxidation of selenite (Se^IV) and sulfite (S^IV) to selenate (Se^VI) and sulfate (S^VI), respectively. For the oxidation of sulfite, computational model A, which resembles the SO active site, is clearly the best choice (lowest barrier, minor exothermicity). For the reduction of selenate, a smaller activation is computed for model A; however, the reaction is less exothermic with model B, which resembles the SeR active site.

Keywords:

• DFT studies
• mononuclear molybdenum enzyme
• redox reaction
• sulfite oxidase (SO)
• selenate reductase (SeR)
• nitrate reductase (NR)

Acknowledgements

The author is highly thankful to Dr. Matthias Hoffmann, Heidelberg University, for continuous guidance throughout this project. Author is also obliged to Graduate Kollege 851 (GK-850), Heidelberg University and Supper computing lab (ScREC) of Research Center for Modeling & Simulation, National University of Sciences and Technology for providing facility to complete this project.