The compounds proposed in this study will be evaluated as magnetic and spectroscopic mimics of the strongly magnetically coupled Fe (III)- Cu(II) binuclear pair of the terminal respiratory enzyme cytochrome c oxidase in the belief that such investigations will further our understanding of this enzyme. Although the complete structure of this enzyme is unknown, it is known that a heme iron (III) is magnetically coupled to a copper(II) through a bridging ligand which could be an imidazolate or thiolate. It is reasonable to investigate the magnetic properties of this system by examining simple complexes which contain the salient features of the enzyme. The experiments proposed in this work will examine two important properties of iron porphyrins which are relevant to the understanding of heme systems in general and to cytochrome c oxidase in particular. The first is the spin state of five coordinate iron (II) porphyrin monoadducts with an imidazole donor. The second is the extent of imidazolate mediated magnetic coupling which can occur between an iron atom in a porphyrin environment and a paramagnetic copper(II). The approach used here will be to design a series of metal chelates (M=Cu(II) or Ni(II)) which contain a covalently bound imidazolate. These complexes, when reacted with iron porphyrins, will form axial adducts as do other imidazole derivatives. Steric restrictions placed on the metal imidazolate complex will insure formation of monoadducts which will be binuclear imidazolate bridged complexes of iron porphyrins. Experiments conducted on these complexes will probe the spin state and magnetic coupling properties of iron(II) and iron(III) compounds. The nickel complexes will serve as diamagnetic blanks for the copper ones. In this manner the spin state of the iron atom can be investigated from the Fe-Im-Ni complexes and the magnetic coupling properties with the Fe-Im-Cu ones. The determination of spin state will be based on Electron Spin Rsonance, Mossbauer, and magnetic susceptibility experiments and the magnetic coupling on variable temperature magnetic susceptibility experiments. Full structural characterization of these complexes will allow for a detailed magnetostructural correlation of this type of iron porphyrin. The results will be used to interpret the magnetic properties of cytochrome c oxidase with an emphasis on structural implications.
