Manganese active sites play a key role in oxygen membolism through participation in superoxide and peroxide defense mechanisms, oxygen activation chemistry, and dioxygen biosynthesis. In contrast to the relatively well-studied Fe and Cu complexes involved in oxygen chemistry, an sites are just beginning to be studied in details and the most effective probes have yes to be defined. We plan to systematically develop a combination of powerful spectroscopic approaches including optical absorption, CD and low temperature MCD over the UV-VlS-near IR spectral range complemented by EPR and SQUID susceptibility measurements to explore the Sround and excited sites of biological in complexes and probe small molecule interactions with these active sites. Our initial focus will be on detailed spectroscopic studies of the mononuclear site in on SD and the binuclear Mn cluster in Mn pseudocatalase, in all their accessible redox sites and with exogenous ligand perturbations. Parallel studied on inorganic models will complement the studied of manganoenzymes, providing valuable spectral calibration and a basis for evaluating the information confined in the spectra of the biological complexes. Manganese coordination complexes representing each of the key oxidation statues in limiting geometries for both ononuclear and binuclear Mn will be prepared and analyzed using the combination of spectroscopies approach for maximum resolution of the d-->d and charge transfer spectra. This rich spectral information will be interpreted using powerful methods of ligand field theory, leading to a description of the metal ions and their ligand interactions in electronic structural detail. Key insights developed in the initial studies on this set of relatively simple and well defined Mn centers will be extended to the binuclear Mn active site in Mn-dependent ribonucleotide reductase and the photosynthetic 02-evolving site, providing information on the structures and ligand interactions in these important and interesting active sites.
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