Spectroscopic Studies of Copper, Iron Sulfur and Heme Electron Transfer Active Sites

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This award in the Inorganic, Bioinorganic, and Organometallic Chemistry Program supports research by Dr. Edward I. Solomon, Chemistry Department, Stanford University, on metal-mediated electron transfer in systems of biological interest. The systems to be investigated are blue copper, copper A, rubredoxin, the 2, 3, and 4 iron-sulfur clusters, and the cytochromes. A combination of spectroscopic methods will be used to: 1) explore the roles of the axial ligands in determining the electronic and geometric structures of the blue copper and copper A centers and their contributions to ET reactivity; 2) define covalent pathways in blue copper and copper A centers for long range electron transfer; 3) define specific electronic structure contributions to the low reduction potential of the Fe(SR)4(1-/2-) center, and the change in electronic structure of the iron sulfur clusters with oxidation using variable energy photoelectron spectroscopy; 4) probe differences in bridged sulfide bonding that can contribute to differences in electron delocalization in 2, 3, and 4 iron clusters and heterometal clusters and the effects of the protein on the electronic structure of the clusters using sulfur K-edge X-ray absorption methodology; and 5) define the covalent delocalization of the redox active orbital into the porphyrin ligand in the cytochromes using metal L-edges. The studies will utilize a wide range of spectroscopic methods, including EPR, polarized single crystal electronic absorption, resonance Raman, circular dichroism, PES, and X-ray absorption edge spectroscopy. Electronic structure calculations will be used to interpret spectral features and their associated electronic structures.These studies will help determine the contribution of electronic structure to long range electron transfer and the role of the protein in determining the geometry and electronics of the active site. The proteins studied are important in biotechnology, nitrogen fixation, respiratory metabolism, and photosynthesis. Spectroscopic methods developed will have applications in biology and catalysis. Postdoctoral and graduate students involved in this research will be trained in a wide range of spectroscopic methods, ligand field and molecular orbital calculations, and enzymology, and will be well prepared for positions in academia or industry. Instrumentation will be made available to members of the bioinorganic community, many from locations outside the U.S.