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Sulfur K-edge XAS of WVO vs. MoVO bis(dithiolene) complexes: contributions of relativistic effects to electronic structure and reactivity of tungsten enzymes.

ABSTRACT: Molybdenum- or tungsten-containing enzymes catalyze oxygen atom transfer reactions involved in carbon, sulfur, or nitrogen metabolism. It has been observed that reduction potentials and oxygen atom transfer rates are different for W relative to Mo enzymes and the isostructural Mo/W complexes. Sulfur K-edge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations on [Mo(V)O(bdt)(2)](-) and [W(V)O(bdt)(2)](-), where bdt=benzene-1,2-dithiolate(2-), have been used to determine that the energies of the half-filled redox-active orbital, and thus the reduction potentials and MO bond strengths, are different for these complexes due to relativistic effects in the W sites.

SUBMITTER: Tenderholt AL

PROVIDER: S-EPMC2940715 | biostudies-literature | 2007 Nov

REPOSITORIES: biostudies-literature

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Sulfur K-edge XAS of WVO vs. MoVO bis(dithiolene) complexes: contributions of relativistic effects to electronic structure and reactivity of tungsten enzymes.

Tenderholt Adam L AL Szilagyi Robert K RK Holm Richard H RH Hodgson Keith O KO Hedman Britt B Solomon Edward I EI

Journal of inorganic biochemistry 20070721 11-12

Molybdenum- or tungsten-containing enzymes catalyze oxygen atom transfer reactions involved in carbon, sulfur, or nitrogen metabolism. It has been observed that reduction potentials and oxygen atom transfer rates are different for W relative to Mo enzymes and the isostructural Mo/W complexes. Sulfur K-edge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations on [Mo(V)O(bdt)(2)](-) and [W(V)O(bdt)(2)](-), where bdt=benzene-1,2-dithiolate(2-), have been used to dete ...[more]

PMID: 17720249

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Project description:Sulfur K-edge X-ray absorption spectroscopy (XAS) spectra of the monodentate sulfate complexes [MII(itao)(SO4)(H2O)0,1] (M = Co, Ni, Cu) and [Cu(Me6tren)(SO4)] exhibit well-defined preedge transitions at 2479.4, 2479.9, 2478.4, and 2477.7 eV, respectively, despite having no direct metal-sulfur bond, while the XAS preedge of [Zn(itao)(SO4)] is featureless. The sulfur K-edge XAS of [Cu(itao)(SO4)] but not of [Cu(Me6tren)(SO4)] uniquely exhibits a weak transition at 2472.1 eV, an extraordinary 8.7 eV below the first inflection of the rising K-edge. Preedge transitions also appear in the sulfur K-edge XAS of crystalline [MII(SO4)(H2O)] (M = Fe, Co, Ni, and Cu, but not Zn) and in sulfates of higher-valent early transition metals. Ground-state density functional theory (DFT) and time-dependent DFT (TDDFT) calculations show that charge transfer from coordinated sulfate to paramagnetic late transition metals produces spin polarization that differentially mixes the spin-up (?) and spin-down (?) spin orbitals of the sulfate ligand, inducing negative spin density at the sulfate sulfur. Ground-state DFT calculations show that sulfur 3p character then mixes into metal 4s and 4p valence orbitals and various combinations of ligand antibonding orbitals, producing measurable sulfur XAS transitions. TDDFT calculations confirm the presence of XAS preedge features 0.5-2 eV below the rising sulfur K-edge energy. The 2472.1 eV feature arises when orbitals at lower energy than the frontier occupied orbitals with S 3p character mix with the copper(II) electron hole. Transmission of spin polarization and thus of radical character through several bonds between the sulfur and electron hole provides a new mechanism for the counterintuitive appearance of preedge transitions in the XAS spectra of transition-metal oxoanion ligands in the absence of any direct metal-absorber bond. The 2472.1 eV transition is evidence for further radicalization from copper(II), which extends across a hydrogen-bond bridge between sulfate and the itao ligand and involves orbitals at energies below the frontier set. This electronic structure feature provides a direct spectroscopic confirmation of the through-bond electron-transfer mechanism of redox-active metalloproteins.

Dataset Information

Sulfur K-edge XAS of WVO vs. MoVO bis(dithiolene) complexes: contributions of relativistic effects to electronic structure and reactivity of tungsten enzymes.

Publications

Sulfur K-edge XAS of WVO vs. MoVO bis(dithiolene) complexes: contributions of relativistic effects to electronic structure and reactivity of tungsten enzymes.

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