Polynuclear Clusters in Biology - Structure, Reactivity

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The oxidation and reduction of various substrates in living organisms are of fundamental importance to life sustaining processes. Multi-electron transfer processes, although less frequent in nature are of equally great importance. Included among the latter are: the 6e-reduction of N2 to ammonia in nitrogenase, the 6e-reduction of sulfite to sulfide and of nitrite to ammonia in sulfite and nitrite reductases respective And the 4e- oxidation of 2H20 to O2 in photosynthesis. This proposal is concerned with the synthesis and study of synthetic analogs for a) metalloenzymes involved in multi-electron reduction and b) the non-porphyrin, non-Fe/S, iron centers active in oxidation processes. Specifically,: the synthesis, structures, spectroscopic properties and reactivitys of Fe/M/S (M=Mo,V) proposal. The Fe/M/S clusters are expected to sere as synthetic analogs for the Fe/M/S centers in the nitrogenases and alternate nitrogenases that contain vanadium or iron in place of molybdenum. The new types of Fe/S clusters that will be synthesized are designed as models for the P- clusters of nitrogenase. Superamolecular assemblies with attended Fe/S clusters containing pi acceptor ligands will be synthesized., and their possible function in the bimetallic activation and catalytic reduction of dinitrogen will be investigated. Multi-nuclear, mixed-ligand, carboxylate-catecholate complexes of first row elements will be studied as structure and reactivity models for the active sites in enzymes that catalyze the multi-electron oxidation of various substrates. The function of the catecholate ligands in these compounds, as storage sites of oxidizing equivalents, will be determined.