Our research objective is to synthesize and fully characterize new types of metal-thiolate complexes for the purpose of obtaining fundamental information about the structural, spectroscopic and reactivity properties of proteins containing metal-cysteine interactions. The metal-cysteine ligation mode occurs in a wide range of metalloproteins. Our approach is to use sterically hindered thiolates to create new types of complexes which mimic some to the more unusual properties exhibited by metal-cysteine centers in metalloproteins. The rational leading to this approach is derived from the analogy and the fact that proteins act as sterically bulky ligands. Extensive results obtained in our laboratory have demonstrated that these ligands react with metals: (1) to form monomeric rather than cluster compounds and (2) to stabilize metals in their higher oxidation states. Using this approach, we have prepared synthetic analogs (e.g., [Fe(SR)4]-) for the oxidized form of rubredoxin and synthetic analogs (e.g., [Fe4S4(SR)4]-) for the oxidized form of high potential iron-sulfur proteins. In addition, it is proposed that similar strategies be used to synthesize analogs for proteins containing: iron (iron-sulfur proteins and enzymes); copper (blue copper and cytochrome oxidase); nickel (hydrogenase); and molybdenum (nitrogenase, xanthine oxidase/dehydrogenase, aldehyde oxidase, sulfite oxidase and nitrate reductase). The reactivity properties of these compounds will also be investigated. Chemico-physical studies of these model compounds will be used to achieve a fundamental understanding of the relationship between the spectroscopic and the structural and electronic properties of the metal center. In addition, the spectroscopic parameters determined form a variety of metal-thiolate model compounds whould be useful to biochemists in their efforts to identify and distinguish different types of metal-cysteine coordination modes. A number of spectroscopic techniques will be used to characterize the compounds including: X-ray crystallography, magnetic susceptibility, electrochemical, electronic, vibrational, MCD, NMR, ESR, EXAFS and Mossbauer measurements.
