Function and Physical Chemistry of a Novel Porphyrin Isomer, Corrphycene.

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Purpose of the proposed research is the functional and physicochemical analysis of a novel structural isomer of porphyrin, corrphycene. The meso-carbon array in corrphycene is in (2, 1, 0, 1), in remarkable contrast with the (1, 1, 1, 1) array in regular porphyrin. The metal cavity in corrphycene is trapezoidal. The reactivity of the iron atom in trapezoidal core is expected to be distinct from that of regular heme iron.The reactivity of iron (III) corrphycene in organic solvent toward 1-methylimidazole was examined. Spectroscopic analysis revealed the appreciable accumulation mono-adduct of 1-methylimidazole during the ligand titration, contrary to iron (III) porphyrin that does not form the mono-adduct. The observation in corrphycene demonstrates that the out-of-plane configuration of iron atom is stabilized with the trapezoidal deformation of e metal cavity.We further analyzed the biological function of iron (II) corrphycene as the prosthetic group of hemoprotein. The myoglobin reco … More nstituted with ferrous corrphycene was fund to be functionally active to reversibly bind oxygen and carbon monoxide. Quantitative analysis, however, revealed that the functional anomalies : the association constants for oxygen and carbon monoxide are extremely low. The affinities of etiocorrphycene-substituted myoglobin for oxygen and carbon monoxide are only 1/13 and 1/128, respectively, as compared with those of native myoglobin. The infrared analysis of corrphycene myoglobin indicates that the iron-CO bond is weakened. The functional and structural anomalies are suggested to arise from decreased iron-CO interactions owing to the larger iron (II) displacement from the plane of corrphycene.The azide complex of iron (III) corrphycene is in an equilibrium between the high-(S=5/2) and low-spin (S=1/2) states, and the equilibrium position is much susceptible to the core deformation of the porphyrin macrocycle. We investigated the magnetic property of the iron (III) in the azide complex of corrphycene myoglobin to support the larger displacement of the iron in corrphycene. The temperature-dependent visible absorption changes revealed that the iron (III) is 80% high-spin. The high-spin fraction is one-order of magnitude larger than 8% reported for native myoglobin. The accompanied infrared observation consistently indicated that the high-spin band is 4-fold larger than the low-spin peak. The anomalous high-spin bias of the equilibrium is fully consistent with the large displacement of the iron from the corrphycene plane. The electron spin resonance spectrum of azide complex demonstrates that the iron-histidine bond is cleaved at 5 K.Anomalous break of the iron-histidine bond was ascribed to the weakened axial bond of the corrphycene-substituted myoglobin.In summary, we revealed unique properties of the iron corrphycene. The abilities of corrphycene iron are substantially modified by the geometric strain in the equatorial coordination core. Therefore, corrphycene is a promissing and potential modulator of the functions of hemoproteins. Less