Spectroscopic and Electrochemical Studies on the Structure and Catalytic Activity of Oxygenase Model Complexes

1.作为加氧酶的模型反应，新开发了钴-席夫碱配合物Co(Sb)催化的氧化反应：烯烃与NaOCl的环氧化反应、烯烃与氧气的单氧合反应、胺与叔丁基氢过氧化氢的脱氢反应(TBHP)。这些反应对Co(Sb)的结构很敏感。为了阐明Co(Sb)的结构对反应活性的影响，合成了不同类型的Co(Sb)，并系统地测定了它们的氧化还原电势E。电化学性质E与结构因素密切相关：Sb配体中吸电子基团较多或体积较大的络合物，以及具有非平面配体的络合物，其电化学性质E较高。在Co(Sb)催化的环氧化反应中，反应物种是与C10配位的水溶性阴离子Co(Sb)，E越高，活性络合物的浓度越高。在另一个ha…上此外，在Co(Sb)催化的烯烃和烯烃与分子氧的单氧化反应中，没有观察到反应活性与E的关系，但络合物的形状起着更重要的作用。由于Co(Sb)的催化活性与P450相似，因此Co(Sb)在TBHP催化胺类脱氢反应中具有重要作用。这种情况下的反应物种是Co(Sb)(t-Bu00)络合物。在反应条件下，过氧络合物分解生成ClO，ClO从衬底中的氮原子中提取电子。黄酮醇-Co(Salen)在非配位溶剂中不易发生氧化分解，得到单晶。X-射线分析表明，底物阴离子以双齿配位形式配位。对该配合物在DMF中的核磁共振研究表明，底物阴离子以单齿配位的形式存在。Co(Sb)和Co(PA)(PA=多胺)对邻苯二酚类加氧酶活性的光谱-磁学和电化学研究表明，在Co(II)催化剂作用下，氧首先被还原为超氧物种，然后从底物向生成的Co(III)形成一个电子转移，形成一个由氢过氧基钴(III)-底物半喹酮组成的三元络合物。另一方面，从Co(III)态开始，质子从底物转移到络合物的阴离子配体，然后电子从底物阴离子转移到Co(III)中心，形成顺磁性的半喹酮络合物中间体，通过磁化率方法得到证实。在1989-1990年的研究中，系统地积累了与作为加氧酶反应中间体的血红素-过氧化氢络合物结构有关的光谱参数。从光谱获得的特征观点出发，研究了过氧血红素络合物形成所需的条件。我们发现，在低温下，在Fe(II)-氧络合物中加入抗坏血酸钠，形成了六配位的过氧化氢-血红素络合物。作为色氨酸双加氧酶反应中间体的另一种模型，ESR证实了六配位的血红素-有机过氧物络合物的形成，该络合物具有包括合成血红素、氧气和底物在内的三元络合物结构。这些结果对于了解自然界中血红素催化氧化反应的机理具有重要意义。较少

1. As model oxygenase reactions, the following cobalt Schiff base complex, Co (SB), catalyzed oxidations have been newly developed : epoxidation of olefins with NaOCl, monooxygenation of alkynes with oxygen, dehydrogenation of amines with t-butyl hydroperoxide (TBHP). These reactions were sensitive to the structure of Co (SB). With the aim of elucidating the effect of the strutture of Co (SB) on the reactivities, various Co (SB) were synthesized and redox potential E of Co (II) = Co (III) for these complexes were systematically determined. The electrochemical characteristics E was closely related to the strucural factors : a higher E was obtained with complexes having more electron-withdrawing or bulkier groups in the SB ligand, and also with complexes having nonplanar ligands. In the Co (SB) catalyzed epoxidation, the reactive species was found to be a water soluble anionic Co (SB) coordinating C10, and the higher E gives the higher concentration of the active complex. On the other ha … More nd, in the Co (SB) catalyzed monooxygenation of alkenes and alkynes with molecular oxygen, no relation between the reactivity and E was observed, but the shape of the complex plays a more important role. The catalysis of Co (SB) in the dehydrogenation of amines with TBHP is important because of a mimic of the P450 activity. The reactive species in this case is a Co (SB) (t-Bu00) complex. Under the reaction conditions, the peroxo complex decomposes to give ClO, which abstracts electron from the nitrogen atom in the substrate. Single crystal was obtained from a flavonolato-Co (salen), which is unsusceptible to the oxygenolysis in noncoordinative solvents. The X-ray analysis of this complex showed that the substrate anion is coordinated as a bidentate ligand. The NMR studes on this complex in DMF, where the complex undergoes readily oxygenolysis, showed that the substrate anion is coordinated as a monodentate ligand.2. Spectro-magnetic and electrochemical studies on the oxygenase like activity of Co (SB) and Co (PA) (PA=polyamines) towards catechols showed that starting with a Co (II) catalyst oxygen is first reduced to superoxo species followed by one-electron transfer from the substrate to the resulting Co (III) resulting in the formation of a ternary complex consisting of hydroperoxo-Co (III) -substrate semiquinone. On the other hand, starting from a Co (III) state, proton transfer from the substrate to an anion ligand of the complex followed by electron transfer from the resulting substrate anion to the Co (IIII) center to form a paramagnetic semiquinone complex intermediate, as confirmed by means of magnetic susceptibility method.3. Spectroscopic parameters related to the structure of heme-peroxide complex as models for the intermediate of oxygenase reactions are systematically accumlated during the research from 1989 to 1990. From the characteristic point of view thus obtained in the spectroscopy, coditions required for the formation of the peroxo heme complexes have been investigated. We find that the addition of sodium salt of ascorbic acid to a Fe (II)-oxygen complex at low temperature gives a 6 coordinate hydrogenperoxido-heme complex.As another model for a possible intermediate in the tryptophan dioxygenase reaction, the formation of a 6 coordinate heme-organic peroxid complex having a ternary complex structure including synthetic heme, oxygen, and the substrate are confirmed by ESR.These results are significant in order to give basic knowledge to understand the mechanism of the oxygenation reactions catalyzed by heme in nature. Less