Study on Metalloenzymes with use of Artificial Supramolecules

金属酶在生物系统中发挥着广泛的作用。大多数化合物的结构和反应机理尚未得到很好的表征。特别是酶的不稳定性是阐明它们的主要障碍。本课题主要研究了高等植物和蓝藻PSII中的细胞色素c_3电子传递系统和细菌锰过氧化氢酶（Mn-CAT）及放氧复合物（OEC）的模型化。蒽连接的卟啉二聚体和四聚体可以形成相应的“咪唑压缩”配合物，这表明Fe（III）离子之间存在较大的反铁磁耦合，其还原电位负移。这些化合物被认为是细胞色素c_3的良好模型化合物。其次，我们研究了含锰酶的模型，包括叶绿体中的锰过氧化氢酶和放氧复合物。两者都具有释放O_2的功能。为了构建其功能模型来模拟氧的释放，我们使用锰卟啉，其在较高的氧化态下相当稳定，并且根据其氧化态显示出特征性的UV-可见光谱。在H_2O_2的还原反应中，锰卟啉的最佳分离度为4.0A。这种锰卟啉二聚体对水的四电子氧化放出O_2也有催化活性。这是使用具有结构明确的结构的锰络合物催化氧化水的第一个实例。

Metalloenzymes play versatile roles in biological systems. Most of them have not well-characterized on their structures and reaction mechanisms. Especially, the instability of the enzymes is the major obstacle to elucidate them. In this research project, we have studied modeling of (1) electron transporting system in cytochrome c_3, and (2) manganesecontaining enzymes involved in oxygen evolving processes : bacterial manganese catalase (Mn-CAT) and oxygen evolving complex (OEC) in PSII of higher plants and cyanobacteria. Athracene-linked porphyrin dimers and tetramer can form the corresponding 'imidazoratesqueezed' complexes, which indicated large antiferromagnetic coupling between the Fe (III) ions and negative shifts on their reduction potential. These compounds are considered to be good models of cytochrome c_3. Next, we studied on the modeling of manganese containing enzymes, which involve manganese catalases and oxygen evolving complex in chloroplast. Both of them have function to evolve O_2. To construct their functional model to mimic the oxygen evolution, we used manganese porphyrins, which were considerably stable at their higher oxidation states and showed characteristic UV-vis spectrum depending upon their oxidation states. In the disproportionation of H_2O_2, we found the optimum Mn-Mn separation to attain high catalase activity to be 4.0 A.Such manganese porphyrin dimers also have catalytic activity on the evolution of O_2 by four-electron oxidation of water. This is the first example of the catalytic oxidation of water with use of manganese complexes possessing structurally well-defined structure.