Mechanistic analysis of metal-oxygen active species and their synthetic application to new catalytic oxidation

本研究旨在通过对反应中间体的光谱表征，阐明人工模型络合物对血红素酶的氧气活化过程，这些中间产物是通过相应的氧气加合物的γ射线(单电子还原)低温放射分解产生的过氧血红素和氢过氧血红素物种。所用的络合物具有基本官能团的模拟，a)轴向配体，b)与氧的氢键，发现于血红素酶的活性部位。氧配合物的2K低温放射分解生成的物种可归属于低自旋六配位的过氧铁血红素。在133K下热处理后，形成了氢过氧基物种。这些结果证实了该配合物可以重现氧活化过程的第一个重要部分，包括配位氧的还原和生成的过氧基团的质子化。合成了在金属中心附近带有四个或两个环烷基的铁卟啉配合物作为前列腺素H合成酶的模型。在该酶的催化循环中，酪氨酸残基被氧化为苯氧基，从而提取聚烯烃底物的特定氢原子。用过氧酸氧化该模型络合物，得到了由萘氧基和铁离子组成的活性物种，如酶中观察到的那样。活性物种可以将非共轭二烯底物氧化成相应的过氧化氢，回收起始的添加了萘酚的铁络合物。用X-射线单晶衍射法确定了其中一个模型化合物的结构。

This study is intended to clarify the dioxygen activation process by artificial model complexes for heme enzymes through the spectroscopic characterization of the reactive intermediates such as peroxo-and hydroperoxo heme species, which are generated by the cryoradiolysis with γ-ray (one-electron reduction) of the corresponding dioxygen adducts. The employed complexes have the mimics of the essential functional groups, a) axial ligand, b) hydrogen bondings toward dioxygen, found in the active sites of heme enzymes. The resulting species from the 2K-cryoradiolysis of oxy-complex was assignable to a low-spin six-coordinated peroxoferric heme. After annealing at 133K, a hydroperoxo species was formed. These results confirm that the present complex can reproduce the first important part of the dioxygen activation process composed of the reduction of the coordinated dioxygen and the protonation of the resulting peroxo group.Iron porphyrin complexes, which bear four or two naphtholic hydroxyl groups in the vicinity of the metal center, were synthesized as models of prostaglandin H synthase. In the catalytic cycle of this enzyme, the tyrosyl residue is oxidized to the phenoxyl radical, which abstracts the specific hydrogen atom of the polyolefinic substrate. The present model complexes were oxidized with peroxy acid to give the active species composed of naphthoxyl radical and ferryl ion, as observed in the enzyme. The active species can oxidize non-conjugated diene substrate to the corresponding hydroperoxide with the recovery of the starting naphthol-appended ferric complex. The structure of one of the model complexes was determined by X-ray crystallography.