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The electronic structures of the cis-MoOS unit is studied by using S K-edge X-ray absorption spectroscopy (XAS) and vibrational spectroscopies coupled with bonding calculations. The electronic structure of the oxidized enzyme site has played a role in polarizing a substrate carbon center for nucleophilic attack by metal activated water and has acted as an electron sink in the two-electron oxidation of substrates.

The reduction potential of sulfite oxidase and relevant models is modulated by sulfur donor effective nuclear charge and nonplanarity of the dithiolelne chelate through changes in the S p-Mo d orbital overlap. In sulfite oxidase, this overlap may be dynamic and effectively mediate charge redistribution during atom and electron transfer and Raman spectra show that mixed-mode Mo-S vibrations of the Mo-dithiolene core, consistent with pseudo-o S(sub dithiolene)-Mo d(sub xy) bonding, may control electron transfer reactivity.

The electronic structure of the unique desoxo Mo-bisdithiolene active sites found in dimethylsulfoxide reductase (DMSOR) enzyme family is evaluated by using symmetrized model compound analogues of the reduced DMSOR active site probed by electronic absorption and resonance Raman spectroscopies. The studies have provided an electronic-structure basis for understanding oxo-transfer and electron-transfer reactivity in members of the DMSOR enzyme family.

A study reports the synthesis and characterization of the first Mo(super V)O(mu-S)Cu complexes that model the core unit of the paramagnetic form of active carbon monoxide dehydrogenase (CODH). Extensive electronic delocalization over the Mo(mu-S)Cu is verified as the origin of the enzyme's unusual electron paramagnetic resonance (EPR) signal.

Research has been conducted on the zerovalen niobium and tantalum complexes. The synthesis and characterization of these complexes have been carried out and their oxidation states have been investigated via the use of density functional theory.

Density functional theory provides new insights into the structural isomerism observed in the cyclopentadienyl-capped iron-sulfur cluster, [(C[sub 5]H[sub 5])[sub 4]Fe[sub 4]S[sub 4]][sup 2+]. Two distinct, closely spaced minima have been located, a triplet with D[sub 2] symmetry and a C[sub 2]-symmetric singlet, both of which correspond closely to the structure of one of the known crystal forms of the cation. Thus, the structural diversity in these species reflects genuine molecular bistability rather than simple solid-state packing effects. In contrast, no stable D[sub 2d]-symmetric minimum has been located, suggesting that the reported D[sub 2d] symmetry of the cation in [(C[sub 5]H[sub 5])[sub 4]Fe[sub 5]S[sub 4]][PF[sub 6]][sub 2] may be a crystallographic artifact. In the ruthenium analogue, the more diffuse 4d orbitals stabilize the C[sub 2]-symmetric singlet, which is unambiguously the ground state, but the D[sub 2]-symmetric potential energy surface provides a viable low-energy pathway for the dynamic exchange of the Ru-Ru bonds. [ABSTRACT FROM AUTHOR]

The molybdenum hydroxylases catalyze the oxidation of numerous aromatic heterocycles and simple organics and, unlike other hydroxylases, utilize water as the source of oxygen incorporated into the product. The electronic structures of the c/s-MoOS units in CoCp2[Tp/PrMovOS(OPh)] and Tp/PrMoVOS(OPh) (Tp/Pr = hydrotris(3-isopropylpyrazol-1-yl)borate), new models for molybdenum hydroxylases, have been studied in detail using S K-edge X-ray absorption spectroscopy, vibrational spectroscopy, and detailed bonding calculations. The results show a highly delocalized Mo=S Π* LUMO redox orbital that is formally Mo(dxy) with ∼35% sulfido ligand character. Vibrational spectroscopy has been used to quantitate Mo-Ssulfido bond order changes in the cis-MoOS units as a function of redox state. Results support a redox active molecular orbital that has a profound influence on MoOS bonding through changes to the relative electro/nucleophilicity of the terminal sulfido ligand accompanying oxidation state changes. The bonding description for these model cis-MoOS systems supports enzyme mechanisms that are under orbital control and dominantly influenced by the unique electronic structure of the cis-MoOS site. The electronic structure of the oxidized enzyme site is postulated to play a role in polarizing a substrate carbon center for nucleophilic attack by metal activated water and acting as an electron sink in the two-electron oxidation of substrates. [ABSTRACT FROM AUTHOR]