New Oxygen Activation Reaction with Rationally Designed Metal Complexes

本研究的目的是阐明两种酶的反应机理，这两种酶分别在双氧和水之间起相互转化作用。细胞色素c氧化酶四电子还原的详细反应机理尚不清楚，但活性位点周围各组分的作用尚不完全清楚。在这些情况下，我们用化学模型得到了两个主要结果。还原形式的N_4Cu络合物-拴系血红素的氧化得到稳定的过氧络合物。它的晶体结构被成功地揭示，表明O_2以“侧对”的方式结合形成μ-η^2:η^1结构。这为讨论异核络合物的化学性质提供了一个很有意义的观点。我们制备了以酪氨酸交联咪唑酸盐作为Cu_B配体的CcO活性位点模型。相应的过氧化物配合物表现出不同的分解途径，生成血红素Fe(III)-OH/Cu（II）。因此，酚羟基在O_2配合物的反应中起着重要的作用。水的氧化是维持地球生命的关键反应。我们完成了Mn（III）卟啉二聚体的化学计量氧化，该二聚体在阴极条件下催化水氧化。经过过酸氧化，生成了稳定性良好的Mn(V)-O络合物，并通过光谱方法确定了其结构。这是Mn(V)=O络合物的第一个例子，它被很好地表征。通过在Mn(V)=O的溶液中加入一种酸，可以几乎定量地自发地生成O_2。因此，我们成功地证明了[Mn(V)=O]_2氧化水。

The aim of this research is the elucidation of the reaction mechanism working in two enzymes, which play the interconversion between dioxygen and water, respectively. The detailed reaction mechanism for the four-electron reduction of cytochrome c oxidase has not clarified yet, but the role(s)of the each component around the active site is not fully understood. We obtained two major results on these account s with chemical models.1.The oxygenation of the reduced form of N_4Cu complex-tethered heme gave a stable peroxo complex. Its crystal structure was successfully disclosed to show that O_2 bound in a 'side-on' fashion to fom μ-η^2:η^1 structure. This gives a very substantial standpoint to discuss the chemistry of heterodinuclear complexes.2.We prepared CcO active site models, which have a tyrosine-cross linked imidazolate as the part of Cu_B ligand. The correponding peroxide complex showed the different decomposition pathway to give heme Fe(III)-OH/Cu(II). Thus, the phenolic hydroxyl group plays an important role in the reaction of the O_2 complex.Water oxidation is the key reaction to sustain life on the earth. We accomplished stoichiometric oxidation of Mn(III)porphyrin dimer, which has established to catalyze water oxidation under cathodic conditions. Upon oxidation with a peracid, the conesponding Mn(V)-O complex was generated in a good stability and was assigned its structure by spectroscopic methods. This is the first example of Mn(V)=O complex, which is well characterized. By the addition of an acid to the solution of Mn(V)=O spontaneously evolved O_2 in almost quantitative yield. Thus, we succeded to prove that [Mn(V)=O]_2 oxidizes water.