Chemistry ETDs

Author

Regina Mtei

Publication Date

7-2-2011

Abstract

Dimethylsulfoxide reductase (DMSOR) enzyme family members catalyze oxygen atom transfer to or from organic or inorganic substrate and play important roles in the global cycles of sulfur and nitrogen, as well as the detoxification of arsenite. This enzyme has recently been subject of investigation due to its catalytic nature of oxygen atom transfer. This work reports on the electronic structure and reactivity properties of dimethylsulfoxide reductase enzyme studied using spectroscopic and computational methods. The spectroscopic methods included electronic absorption (EA), electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD) and resonance Raman rRaman). Here, we report full characterization of the DMSOR and DMSOR model compounds, MoO/S/Se(LCOOMe)2, MoO(LH/LO)2, MoS/Se(LPh)2, MoO(L2ipro/meth), MoO(SPh)2(Lipro), MoO(bdt)2 and WO/S(LPh)2- and the nature of their charge transfer transitions. The model compounds were studied in the (IV), (V) oxidation states. The electron withdrawing nature of LCOOMe, L2ipro/meth, LPh ligands have indicated the presence of a low energy intraligand charge transfer transition. Ligand field, metal to ligand charge transfer, ligand to metal charge transfer and intraligand charge transfer bands for these model compounds have been successfully assigned using both electronic absorption and rRaman spectroscopies for Mo(IV) compounds. EA and MCD spectroscopic methods enabled the assignment of Mo(V) compounds. The density functional theory calculations have supported our assignments. EPR spectroscopy revealed a rhombic g-tensor and axial A-tensors for Mo(V) compounds indicative of low symmetry coordination and a dxy redox orbital. Spin density calculations revealed that electron transfer is through unbent side of ene-dithiolene ligands for regeneration of Mo(VI) resting state in the catalytic cycle. In particular, for DMSO reductase enzyme, the electronic structure of a desoxo Mo(V) intermediate has been probed by EPR, electronic absorption and MCD spectroscopies. The EPR spectra revealed a rhombic g-tensor that indicated a low symmetry coordination for this intermediate. For the first time a rhombic 95,97Mo A-tensor has been determined, that indicated a dz2 redox orbital admixed with dxy/dx2-y2 type orbitals. In general, these methods have indicated that the geometry of Mo(V) intermediate is distorted trigonal prismatic.

Language

English

Keywords

DMSOR, AO Models, Raman, EPR, MCD, DFT

Document Type

Dissertation

Degree Name

Chemistry

Level of Degree

Doctoral

Department Name

Department of Chemistry and Chemical Biology

First Advisor

Kirk, Martin

First Committee Member (Chair)

Keller, David

Second Committee Member

Guo, Hua

Third Committee Member

Feng, Changjian

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