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

加氧酶模型复合物的结构和催化活性的光谱和电化学研究

基本信息

批准号：
01044134
负责人：
NISHINAGA Akira
金额：
$ 4.22万
依托单位：
Osaka Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

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

1. 作为加氧酶的典型反应，钴希夫碱配合物Co （SB）催化的氧化反应有：烯烃与NaOCl的环氧化反应、炔与氧的单氧反应、胺与过氧化氢t-丁基（TBHP）的脱氢反应。这些反应对Co （SB）的结构很敏感。为了阐明Co （SB）的结构对反应性的影响，合成了各种Co (SB)，并系统地测定了Co (II) = Co （III）的氧化还原电位E。电化学特性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配合物以及具有非平面配体的配合物E较高。在Co （SB）催化的环氧化反应中，反应物质为水溶性阴离子Co （SB）配位C10， E越高，活性配合物浓度越高。另外，在Co （SB）催化烯烃和炔与分子氧的单加氧反应中，反应活性与E无关，而配合物的形状起着更重要的作用。Co （SB）对胺脱氢的催化作用是重要的，因为它模拟了P450的活性。这种情况下的反应物质是Co (SB) （t-Bu00）配合物。在反应条件下，过氧络合物分解生成ClO， ClO从底物中的氮原子中抽离电子。从一种不受非配位溶剂氧解影响的黄酮- co （salen）中得到单晶。该配合物的x射线分析表明，底物阴离子作为双齿配体配位。该配合物在DMF中的核磁共振研究表明，配合物易于氧解，底物阴离子作为单齿配体进行配位。对Co （SB）和Co (PA) （PA=多胺）对儿茶酚类加氧酶活性的波谱磁和电化学研究表明，从Co （II）催化剂开始，氧首先被还原为超氧物质，然后从底物到生成的Co （III）进行单电子转移，形成由氢过氧-Co (III) -底物半醌组成的三元配合物。另一方面，从Co （III）态开始，质子从底物转移到配合物的阴离子配体上，然后电子从底物阴离子转移到Co （IIII）中心，形成顺磁性的半醌配合物中间体，通过磁化率法证实了这一点。作为加氧酶反应中间体模型的血红素-过氧化物络合物结构的光谱参数是在1989年至1990年的研究中系统积累起来的。从光谱学中获得的特征观点出发，研究了形成过氧血红素络合物所需的条件。我们发现抗坏血酸钠盐在低温下加入到铁(II)-氧配合物中得到6配位的过氧化氢-血红素配合物。作为色氨酸双加氧酶反应的另一种可能中间体模型，ESR证实了6配位血红素-有机过氧化物配合物的形成，该配合物具有三元配合物结构，包括合成血红素、氧和底物。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。少