The objectives of this research involve the synthesis and characterization of synthetic analogues of various heme proteins. The reactions of interest include 1) O2, CO and ligand binding by hemoglobin, myoglobin and nonmammalian hemoproteins, 2) O2 activation and hydrocarbon hydroxylation by the monooxygenase cytochrome P-450, and 3) the reaction with and reduction of oxidants by catalase and peroxidase. These enzymes are relevant to cardiovascular functioning; drug, hormone and exobiotic metabolism; and to oxidant detoxification and substrate oxidation. Our studies are directed towards an understanding of the molecular mechanisms of these reactions in closely related model metalloporphyrine. We have synthesized, characterized, and quantitatively studied the 02 and other ligand binding to a series of porphyrinatoiron(II) complexes. Of special interest in our """"""""bis-pocket"""""""" prophyrin, which provides protected pockets on both faces of the macrocyle and which is extremely oxidatively robust. The non-polar nature of this porphyrin's pockets allows us to quantitate the contribution of polarity, hydrogen bonding and other factors of 02 and CO affinities. This porphyrin has also proved useful in dramatically stabilizing high oxidation state complexes which may be analogous to Compounds I and II of peroxidase and catalase and to the active hydroxylase species of cytochrome P-450. In addition, the steric protection of the pocket favors terminal hydroxylation and epoxidation, demonstrating shape-selective substrate recognition. Additional work has been carried out on highly oxidized single atom bridged iron porphyrin dimers which has demonstrated the sensitivity of electronic structure in such systems to the nature of ligation. Continuation of our efforts in these areas should lead to a quantitative understanding of the influences which modulate 02, and CO binding, to the full characterization and isolation of synthetic analogs of high oxidation state heme protein intermediate, and to a closer understanding of substrate shape selectivity and regiospecificity by monooxygenases.
