Geometric Determinants of XANES Structure

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Geometric Determinants of XANES Structure

• Mehmet Karabiyik, Kyle Bolduc, and James E.
  Penner-Hahn
• Department of Chemistry, University of Michigan,
  Ann Arbor, MI, 48109,USA

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X-ray Absorption Spectroscopy (XAS)
XANES - X-ray Absorption Near Edge Structure
EXAFS - Extended X-ray Absorption Fine Structure
a) Newville, M., http//cars9.uchicago.edu/xafs/xa
s_fun/xas_fundamentals.pdf b) X-Ray Absorption
Principles, applications, techniques of EXAFS,
SEXAFS and XANES, (eds. Koningsberger, D. C.,
Prins, R.), John Wiley Sons New York, 1988.
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Environment of the Active Site Zinc
MetH
Active site zinc has three cysteine residues and
a water molecule
MetE
Active site zinc has two cysteine residues, a
histidine residue and a low-Z ligand
Peariso, K. et al. J. Am. Chem. Soc. (1998), 120,
8410-8416. Zhou, Z. S., Peariso, K. Penner-Hahn,
J. E., Matthews, R. G. Biochemistry, 1999, 38,
15915.
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Zinc is required for catalytic turnover in MetH
Matthews, R. G. Acc. Chem. Res. (2001), 34,
681-689
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As With MetH, Zinc is Required for Catalytic
Activity in MetE
González, J. et al. Biochemistry, 1996, 35,
12228-12234.
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XANES changes depend on addition of substrate,
but not on identity of substrate
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XANES differences are identical for Hcy and
SeHcy, and similar for ZnS3(N/O) and ZnS2(N/O)2
sites
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Origin of XANES differences?
Not oxidation state. Not ligation. May be
geometry?
XANES differences for different ZnS2(N/O)2
enzymes are distinct.
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Model Compounds
Ni(Dts)22-
Zn(Dts)22-
Dts1,2-Cyclobutenedione-3,4-dithiolate
Holah, D.G. Hollander, F.J. Coucouvanis, D.
Inorg. Chem. 1975,14,2675-2665 Wenzel, B.
Durutkowski, U. Strauch, P. Z.Anorg.Allg.Chem.20
01, 627, 923
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XANES changes appear to correlate with changes in
geometry
XANES changes appear to correlate with changes in
geometry
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K vs. PPh4
Counter ion is not the main factor in XANES
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Bulk and Doped sample Spectra Comparison
Geometry changes affect XANES dramatically
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Zn(Dts)2(PPh4)2 Data vs. Feff8
BTABenzyltriethylammonium
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K2Ni(Dts)2 and K2Co(Dts)2 Calculations
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Conclusions

• XANES is highly geometry dependent.
• More elaborate calculations need to be done.

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Acknowledgements

• Prof. Dr. James E. Penner-Hahn
• Penner-Hahn Group Members
• NIH

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Systematic Change of Geometry
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Systematic Change of Afolp Card Value