9316768 Solomon Many metalloenzymes exhibit ususual spectral features which reflect novel electronic structures that can make significant contributions to catalysis. This research program focuses on understanding the unusal electronic and geometric structures of active sites in magnetically coupled binuclear non-heme iron and manganese cluster enzymes. Hemerythrin, methane monooxygenase and ribonucleotide reductase have FE(II)Fe(II) sites which bind, activate and reduce O2, respectively, while purple acid phosphatase is active in catalysis in its mixed valent Fe(II)Fe(III) state. The active sites in these proteins can generally be obtained in the Fe(III)Fe(III) , Fe(III)Fe(II) and Fe(II)Fe(II) states and model complexes exist for all of these oxidation states. Oxy- intermediates or analogues are now available for a number of these proteins and for non-heme iron model complexes at the peroxy and oxo-ferryl levels. The manganese-oxo cluster enzymes of interest include manganese catalase, manganese ribonucleotide reductase, manganese substituted iron ribonucleotide reductase and the water oxidation catalyst in Photosystem II. Again, model complexes are available for all the biologically relevant oxidation states from Mn(II)Mn(II) to Mn(IV)Mn(IV) . A spectroscopic approach is presented which emphasizes the application of absorption, circular dichroism,magnetic circular dichroism and resonance Raman methods to study the excited states in these enzymes and model complexes and variable temperature variable field magnetic circular dichroism to probe the ground state sublevel splittings which relate to the bridging ligation responsible for the coupling. The results from these spectroscopies are combined with ligand field and self consistent field-X-scattered wave calculations to determine the electronic structures of these active sites. These studies are directed toward defining active site geometric and electron structure differences which relate t o differences in function in the non-heme iron enzymes, determining active site similarities and differences between the binuclear non-heme iron and manganese enzymes, and understanding the electronic structures of the metal-oxy intermediatesand metal-oxo bonds as related to dioxygen activation and O-O bond formation. %%% Many proteins and enzymes contain metal ion active sites which play a key role in biological function. Often these exhibit ususual spectral features which reflect novel electronic structures that can make significant contributions to calalysis. This research program focuses on understanding the unusual electronic and geometric structures of active sites in magnetically coupled binuclear non-heme iron and manganese cluster enzymes. These clusters are found in hemerythrin (reversible oxygen binding), ribonucleotide reductase (conversion of ribonucleotides to deoxyribonucleotides in DNA synthesis), methane monooxygenase (catalytic conversion of methane to methanol), catalase (detoxification of peroxide), and the water oxidation catalyst in photosystem II (generation of oxygen by green plants). These studies are directed toward defining active site geometric and electronic structure differences which relate to differences in function in the non-heme iron enzymes, determining active site similarities and differences between the corresponding binuclear non-heme iron and manganese enzymes, and understanding the electronic structures of the metal-oxygen intermediates involved in dioxygen activation and O-O bond formation. This research will provide fundamental insight into geometric and electronic structural contributions to function in biology and lay the groundwork for the design and development of new catalytic systems. ***
