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Title: Sulfur K-edge Spectroscopic Investigation of Second Coordination Sphere Effects in Oxomolybdenum-Thiolates: Relationship to Molybdenum-Cysteine Covalency and Electron Transfer in Sulfite Oxidase

Abstract

Second-coordination sphere effects such as hydrogen bonding and steric constraints that provide for specific geometric configurations play a critical role in tuning the electronic structure of metalloenzyme active sites and thus have a significant effect on their catalytic efficiency. Crystallographic characterization of vertebrate and plant sulfite oxidase (SO) suggests that an average O{sub oxo}-Mo-S{sub Cys}-C dihedral angle of {approx}77{sup o} exists at the active site of these enzymes. This angle is slightly more acute ({approx}72{sup o}) in the bacterial sulfite dehydrogenase (SDH) from Starkeya novella. Here we 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 to possess an O{sub ax}-Mo-S{sub thiolate}-C dihedral angle of {approx}90{sup o}. Sulfur X-ray absorption spectroscopy clearly shows that O{sub ax}-Mo-S{sub thiolate}-C dihedral angles near 90{sup o} effectively eliminate covalency contributions to the Mo(xy) redox orbital from the thiolate sulfur. Sulfur K-pre-edge X-ray absorption spectroscopy intensity ratios for the spin-allowed S(1s) {yields} S{sup v}(p) + Mo(xy) and S(1s) {yields} S{sup v}(p) + Mo(xz,yz) transitions have been calibrated by a direct comparison of theory with experiment to yield thiolate S{sup v}(p) orbital contributions, c{sup 2}{sub i}, to the Mo(xy) redox orbital and themore » Mo(xz,yz) orbital set. Furthermore, these intensity ratios are related to a second coordination sphere structural parameter, the O{sub oxo}-Mo-S{sub thiolate}-C dihedral angle. The relationship between Mo-S{sub thiolate} and Mo-S{sub dithiolene} covalency in oxomolydenum systems is discussed, particularly with respect to electron-transfer regeneration in SO.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930320
Report Number(s):
BNL-81030-2008-JA
Journal ID: ISSN 0020-1669; INOCAJ; TRN: US200822%%1468
DOE Contract Number:  
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Inorganic Chemistry; Journal Volume: 46; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; ABSORPTION SPECTROSCOPY; BONDING; COVALENCE; EFFICIENCY; ELECTRON TRANSFER; ELECTRONIC STRUCTURE; ENZYMES; HYDROGEN; OXIDASES; OXIDOREDUCTASES; PLANTS; REGENERATION; SPHERES; SULFITES; SULFUR; SYNTHESIS; TUNING; VERTEBRATES; YIELDS; national synchrotron light source

Citation Formats

Peariso,K., Helton, M., Duesler, E., Shadle, S., and Kirk, M. Sulfur K-edge Spectroscopic Investigation of Second Coordination Sphere Effects in Oxomolybdenum-Thiolates: Relationship to Molybdenum-Cysteine Covalency and Electron Transfer in Sulfite Oxidase. United States: N. p., 2007. Web. doi:10.1021/ic061150z.
Peariso,K., Helton, M., Duesler, E., Shadle, S., & Kirk, M. Sulfur K-edge Spectroscopic Investigation of Second Coordination Sphere Effects in Oxomolybdenum-Thiolates: Relationship to Molybdenum-Cysteine Covalency and Electron Transfer in Sulfite Oxidase. United States. doi:10.1021/ic061150z.
Peariso,K., Helton, M., Duesler, E., Shadle, S., and Kirk, M. Mon . "Sulfur K-edge Spectroscopic Investigation of Second Coordination Sphere Effects in Oxomolybdenum-Thiolates: Relationship to Molybdenum-Cysteine Covalency and Electron Transfer in Sulfite Oxidase". United States. doi:10.1021/ic061150z.
@article{osti_930320,
title = {Sulfur K-edge Spectroscopic Investigation of Second Coordination Sphere Effects in Oxomolybdenum-Thiolates: Relationship to Molybdenum-Cysteine Covalency and Electron Transfer in Sulfite Oxidase},
author = {Peariso,K. and Helton, M. and Duesler, E. and Shadle, S. and Kirk, M.},
abstractNote = {Second-coordination sphere effects such as hydrogen bonding and steric constraints that provide for specific geometric configurations play a critical role in tuning the electronic structure of metalloenzyme active sites and thus have a significant effect on their catalytic efficiency. Crystallographic characterization of vertebrate and plant sulfite oxidase (SO) suggests that an average O{sub oxo}-Mo-S{sub Cys}-C dihedral angle of {approx}77{sup o} exists at the active site of these enzymes. This angle is slightly more acute ({approx}72{sup o}) in the bacterial sulfite dehydrogenase (SDH) from Starkeya novella. Here we 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 to possess an O{sub ax}-Mo-S{sub thiolate}-C dihedral angle of {approx}90{sup o}. Sulfur X-ray absorption spectroscopy clearly shows that O{sub ax}-Mo-S{sub thiolate}-C dihedral angles near 90{sup o} effectively eliminate covalency contributions to the Mo(xy) redox orbital from the thiolate sulfur. Sulfur K-pre-edge X-ray absorption spectroscopy intensity ratios for the spin-allowed S(1s) {yields} S{sup v}(p) + Mo(xy) and S(1s) {yields} S{sup v}(p) + Mo(xz,yz) transitions have been calibrated by a direct comparison of theory with experiment to yield thiolate S{sup v}(p) orbital contributions, c{sup 2}{sub i}, 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, the O{sub oxo}-Mo-S{sub thiolate}-C dihedral angle. The relationship between Mo-S{sub thiolate} and Mo-S{sub dithiolene} covalency in oxomolydenum systems is discussed, particularly with respect to electron-transfer regeneration in SO.},
doi = {10.1021/ic061150z},
journal = {Inorganic Chemistry},
number = 4,
volume = 46,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}