Sulfur K-edge Spectroscopic Investigation of Second Coordination Sphere Effects in Oxomolybdenum-Thiolates: Relationship to Molybdenum-Cysteine Covalency and Electron Transfer in Sulfite Oxidase
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- 作者：Katrina Peariso ; Matthew E. Helton ; Eileen N. Duesler ; Susan E. Shadle ; Martin L. Kirk
- 刊名：Inorganic Chemistry
- 出版年：2007
- 出版时间：February 19, 2007
- 年：2007
- 卷：46
- 期：4
- 页码：1259 - 1267
- 全文大小：166K
- 年卷期：v.46,no.4(February 19, 2007)
- ISSN：1520-510X
文摘
Second-coordination sphere effects such as hydrogen bonding and steric constraints that provide for specific geometricconfigurations play a critical role in tuning the electronic structure of metalloenzyme active sites and thus have asignificant effect on their catalytic efficiency. Crystallographic characterization of vertebrate and plant sulfite oxidase(SO) suggests that an average Ooxo-Mo-SCys-C dihedral angle of ~77
exists at the active site of these enzymes.This angle is slightly more acute (~72) in the bacterial sulfite dehydrogenase (SDH) from Starkeya novella. Herewe report the synthesis, crystallographic, and electronic structural characterization of Tp*MoO(mba) (where Tp* =(3,5-dimethyltrispyrazol-1-yl)borate; mba = 2-mercaptobenzyl alcohol), the first oxomolybdenum monothiolate topossess an Oax-Mo-Sthiolate-C dihedral angle of ~90. Sulfur X-ray absorption spectroscopy clearly shows thatOax-Mo-Sthiolate-C dihedral angles near 90 effectively eliminate covalency contributions to the Mo(xy) redox orbitalfrom the thiolate sulfur. Sulfur K-pre-edge X-ray absorption spectroscopy intensity ratios for the spin-allowed S(1s)
Sv(p) + Mo(xy) and S(1s) Sv(p) + Mo(xz,yz) transitions have been calibrated by a direct comparison oftheory with experiment to yield thiolate Sv(p) orbital contributions, 
, to the Mo(xy) redox orbital and the Mo(xz,yz)orbital set. Furthermore, these intensity ratios are related to a second coordination sphere structural parameter, theOoxo-Mo-Sthiolate-C dihedral angle. The relationship between Mo-Sthiolate and Mo-Sdithiolene covalency in oxomolydenumsystems is discussed, particularly with respect to electron-transfer regeneration in SO.
exists at the active site of these enzymes.This angle is slightly more acute (~72) in the bacterial sulfite dehydrogenase (SDH) from Starkeya novella. Herewe report the synthesis, crystallographic, and electronic structural characterization of Tp*MoO(mba) (where Tp* =(3,5-dimethyltrispyrazol-1-yl)borate; mba = 2-mercaptobenzyl alcohol), the first oxomolybdenum monothiolate topossess an Oax-Mo-Sthiolate-C dihedral angle of ~90. Sulfur X-ray absorption spectroscopy clearly shows thatOax-Mo-Sthiolate-C dihedral angles near 90 effectively eliminate covalency contributions to the Mo(xy) redox orbitalfrom the thiolate sulfur. Sulfur K-pre-edge X-ray absorption spectroscopy intensity ratios for the spin-allowed S(1s) Sv(p) + Mo(xy) and S(1s) Sv(p) + Mo(xz,yz) transitions have been calibrated by a direct comparison oftheory with experiment to yield thiolate Sv(p) orbital contributions, , to the Mo(xy) redox orbital and the Mo(xz,yz)orbital set. Furthermore, these intensity ratios are related to a second coordination sphere structural parameter, theOoxo-Mo-Sthiolate-C dihedral angle. The relationship between Mo-Sthiolate and Mo-Sdithiolene covalency in oxomolydenumsystems is discussed, particularly with respect to electron-transfer regeneration in SO.