Electronic structure description of the cis-MoOS unit in models for molybdenum hydroxylases.
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 cis-MoOS units in CoCp2[TpiPrMoVOS(OPh)] and TpiPrMoVIOS(OPh) (TpiPr = 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 pi* LUMO redox orbital that is formally Mo(dxy) with approximately 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.
Doonan
Christian J
CJ
The Department of Chemistry and Biological Chemistry, The University of New Mexico, MSC03 20601 University of New Mexico, Albuquerque, New Mexico 87131-0001, USA.
Rubie
Nick D
ND
Peariso
Katrina
K
Harris
Hugh H
HH
Knottenbelt
Sushilla Z
SZ
George
Graham N
GN
Young
Charles G
CG
Kirk
Martin L
ML
D001665:Binding Sites; D004583:Electrons; D008667:Metalloproteins / Q000737:chemistry; D006899:Mixed Function Oxygenases / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D008982:Molybdenum; D013057:Spectrum Analysis
D008667:Metalloproteins; D008982:Molybdenum; D006899:Mixed Function Oxygenases