Gated Electron Transfer in Copper(II)/(I) Systems

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With this award, the Inorganic, Bioinorganic, and Organometallic Chemistry Program provides support for a collaborative research project involving Drs. David B. Rorabacher and Ronald R. Schroeder of the Chemistry Department, Wayne State University, and Dr. Leo A. Ochrymowycz of the Chemistry Department, University of Wisconsin-Eau Claire. They will synthesize a series of copper thiaether, thiaamine, and thiapyridine complexes in which both copper (I) and copper(II) oxidation states are accessible. The thirty-one macrocyclic ligands targeted for study are specifically designed to impose differing types of constraints within the ligand framwork. Using cyclic voltammetry, stopped-flow kinetics, NMR line broadening studies, and selected structural determinations, they will investigate the relationship between ligand geometric changes and transfer of electrons to and from the copper centers in these complexes. Under some conditions, the rate of the reaction in one direction will be `gated` by the requirement for the intermediate to undergo a conformational change. Molecular mechanical calculations will be used to compare the energies of reaction intermediates generated during the electron transfer step and develop some predictive capability. Complexes of copper(I) and copper(II) are known to have different geometries, so that upon oxidation or reduction it is likely that conformational changes will occur. A conformational change creates an energy barrier to electron transfer. If this energy barrier can be controlled, then it becomes possible for electron transfer to occur in one direction, that is, to be `gated.` This topic is of considerable current interest in biological chemistry, because it may be important in the reactions of metalloproteins. This research will help answer questions about the extent to which conformational changes in the proteins or around the metal binding site are involved in natural systems, as well as point the way to design of specific catalysts.