SYNTHETIC MU-IMIDAZOLATO AND MU-OXO BINUCLEAR COMPLEXES OF COPPER(II) AND IRON(III) PORPHYRINS AS MODEL COMPOUNDS FOR THE ACTIVE SITE OF RESTING CYTOCHROME C OXIDASE

Several new and unique (mu)-imidazolato and (mu)-oxo binuclear complexes of iron and copper have been synthesized and characterized as models for the active site of cytochrome c oxidase. Characterization of these novel complexes included physical measurements utilizing magnetic susceptibility, ('57)Fe Mossbauer, nmr, epr, mcd, uv-visible, resonance Raman, and infra-red spectroscopy, electrochemistry, and ESCA. (mu)-Imidazolato complexes based on the UroTPP('2-) ligand where UroTPP('2-) is the dianion of urocanic acid have been synthesized via the general route {Fe('III)(UroTPP)Cl} + {M('II)(acac)(,2)} (--->) {Fe('III)(UroTPP)M('II)(acac)(,2)} where M=Cu,Zn and acac=acetylacetonate. The Fe('III)/Cu('II) complex exhibits properties suggestive of two magnetically and electronically isolated high-spin Fe('III) (S=5/2) and Cu('II) (S=1/2) centers. In addition, various solution-dependent measurements indicate that the binuclear complexes retain their integrity in solution. The reduced species {Fe('II)(UroTPP)}, its CO adduct, and its reaction product upon exposure to air (presumably {Fe('III)(UroTPP)}(,2)O)have also been synthesized and characterized as the basis for future modeling studies. For example, future species of the type {Fe('II)(UroTpp)M('II)(acac)(,2)}('-) or {(UroTPP)Fe('III)-O-Cu('II)(imidH)(,2)DAP}('+) should exhibit interesting properties and serve as further models for the active structure. Finally, the first reported oxo-bridged heterobimetallic of copper(II) and an iron(III) porphyrin complex has also been prepared and thoroughly and systematically characterized. Its low temperature synthesis (-78(DEGREES)C) is novel and proceeds via reaction between a ferryl intermediate, (TPP)Fe('IV)=O, and {Cu('I)(imidH)(,2)DAP}('+) to give {(TPP)Fe('III)-O-Cu('II)(imidH)(,2)DAP}('+), which has been isolated as its BF(,4)('-) salt. The magnetochemistry and epr results for this compound indicate the presence of strong antiferromagnetic coupling between the Fe('III) (S=3/2) center and the Cu('II) (S=1/2) center to give a resultant S=1 ground state. This oxo-bridged complex has also been studied by a wide range of solution-dependent techniques which verify its binuclear nature in solution and S=1 magnetic behavior. Results from oxo-bridge lability studies on this complex, the first of its kind, have also been performed and are intepreted in light of similar experiments involving actual resting Cytochrome c Ocidase. Each of the (mu)-imidazolato and (mu)-oxo binuclear complexes described above have been discussed as they pertain to structural models for deciphering the active site structure of Cytochrome c Oxidase