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

本研究的目的是对卟啉的一种新型结构异构体——卟啉进行功能和物理化学分析。卟啉的中位碳排列在（2,1,0,1）上，与常规卟啉的中位碳排列（1,1,1,1）形成鲜明对比。卟啉中的金属腔呈梯形。铁原子在梯形核中的反应性与常规血红素铁的反应性不同。研究了有机溶剂中铁（III）对1-甲基咪唑的反应性。光谱分析显示配体滴定过程中1-甲基咪唑的单加合物明显积累，而铁（III）卟啉不形成单加合物。铁原子的面外构型随着e金属腔的梯形变形得到稳定。我们进一步分析了铁（II）卟啉作为血红蛋白假基的生物学功能。结果表明，含亚铁的肌红蛋白对氧和一氧化碳的可逆结合具有功能活性。然而，定量分析揭示了功能异常：氧和一氧化碳的缔合常数非常低。与天然肌红蛋白相比，依硫卟啉取代的肌红蛋白对氧和一氧化碳的亲和力分别仅为1/13和1/128。对卟啉肌红蛋白的红外分析表明，铁-一氧化碳键被削弱。功能和结构异常可能是由于铁（II）从卟啉平面上位移较大，导致铁- co相互作用减弱所致。铁（III）卟啉叠氮化物配合物处于高自旋态（S=5/2）和低自旋态（S=1/2）之间的平衡状态，该平衡位置极易受到卟啉大环核心变形的影响。我们研究了铁（III）在卟啉肌红蛋白叠氮化物配合物中的磁性，以支持铁在卟啉中的较大位移。随温度变化的可见光吸收变化表明铁（III）为80%的高自旋。高自旋分数比原生肌红蛋白报道的8%大一个数量级。伴随的红外观测一致表明，高自旋带比低自旋峰大4倍。平衡态的异常高自旋偏置与铁从卟啉平面的大位移完全一致。叠氮化物配合物的电子自旋共振谱表明，铁-组氨酸键在5k时发生断裂。铁-组氨酸键的异常断裂归因于卟啉取代的肌红蛋白轴向键的减弱。总之，我们揭示了铁卟啉的独特性质。在赤道配位核中的几何应变极大地改变了卟啉铁的性能。因此，卟啉是一种很有前途和潜在的血红蛋白功能调节剂。少

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