X-Ray Resonance Raman Spectroscopy of Mn and Ni Metalloproteins

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This award by the Inorganic, Bioinorganic and Organometallic Chemistry program supports research by Professor Stephen P. Cramer in the Department of Chemistry and Uwe Bergmann, Assistant Research Scientist in the Department of Applied Sciences, at the University of California at Davis to develop x-ray resonance Raman spectroscopy (XRRS) as a tool to probe low-energy excitations. The low energy transitions will involve charge transfer and d-d bands as well as molecular vibrations involving metal ions in protein systems. In nickel enzymes, with either Fe or Ni, metal 3d to ligand (CO) pi* transitions are obscured by sulfur to iron excitations in Fe-S clusters. In photosystem-II, Mn d-d bands can only be seen over a narrow spectroscopic window above the chlorophyl cutoff and below water near infrared bands. The development of XRRS as applied to protein systems will enable the observation of metal-centered transitions that are obscured by other chromophores, which could help to characterize some of the poorly understood, but important, intermediates in Fe-Ni dehydrogenase, carbon monoxide dehydrogenase, photosystem-II and other important Mn and Ni enzymes that are essential to understanding fundamental biological processes.A new x-ray spectroscopic technique will be developed to probe active sites in important protein centers.