双锰基水氧化仿生分子催化剂的密度泛函理论研究

发布时间：2018-01-31 19:29

本文关键词： 人工光合作用水氧化锰基催化剂密度泛函理论　出处：《中国科学技术大学》2015年博士论文　论文类型：学位论文

【摘要】：人工模拟光合作用系统,利用太阳能光解水制氢,是实现将太阳能转化成清洁的化学能源,从而解决当今社会环境污染和能源危机的一个理想方法。在人工模拟光合系统的设计中,水氧化反应作为人工光合作用体系中电子和质子的来源,是制约太阳能转化的关键因素。因此,开发出高效稳定的水氧化催化剂对于实现太阳能转化至关重要。在众多的水氧化催化剂中,锰基催化剂因为具有与自然界光合体系一致的过渡金属元素(锰元素),受到了特别的关注。得益于量子化学计算方法和高性能计算机运算能力的飞速发展,基于密度泛函理论(Density Functional Theory, DFT)的第一性原理计算方法在分子反应机理的分析和化学性质的预测方面发挥着日益重要的作用。本论文从密度泛函理论计算出发,以仿生的双核锰基水氧化催化剂为立足点,对此催化剂分子的空间和电子结构性质,以及催化水氧化的反应机理进行了系统地考察；在此基础上,基于对双核锰基水氧化催化剂的理解,进一步对催化剂分子的配体结构进行改造,从理论上设计了具有更高催化效率的双核锰基水氧化催化剂。本论文共四章。第1章介绍了本论文的选题背景和依据。从植物光合作用中光系统Ⅱ入手,介绍了人工光合作用系统的组成,从人工光合作用系统中所涉及到的敏化剂、质子还原催化剂和关键的水氧化催化反应来展开。着重介绍了水氧化反应,从水氧化催化剂催化能力的评估,分子水氧化催化剂的机理分析等角度进行阐述。接着介绍了文献中研究较为广泛的分子水氧化催化剂。最后会简要阐述我们所采用的计算方法——密度泛函理论。第2章中,我们初步介绍了本论文的研究对象一一双核锰基水氧化催化剂[H2O(terpy)MnⅢ(μ-O)2MnⅣ(terpy)OH2]3+(terpy=2,2':6',2"-terpyridine,记为Mn配合物1)的实验和理论研究进展,并给出了关于Mn配合物1的结构分析及相关的计算细节。第3章中,我们使用密度泛函方法探讨了两个锰离子中心在几何结构和电子结构上所存在的不对称性,以及这种不对称对化学性质的影响。在研究中,我们计算了Mn配合物1在醋酸缓冲溶液中的稳定构型,并从热力学和动力学这两个角度对两个锰离子中心的不对称进行了详细分析。通过研究发现,因为四价锰离子中心具有更大的空间位阻效应,不利于醋酸根离子的结合,导致了醋酸根离子主要结合在三价锰离子中心上,由此澄清了文献中关于醋酸根离子结合位点的分歧。第4章中,我们以Mn配合物1催化水氧化的反应机理为基础,对此催化剂的配体结构进行改造,从而设计出一种新型的双核锰基催化剂[H2O(2-bpNP)MnⅢ(μ-O)2MnⅣ(2-bpNP)OH2]3+(2-bpNP=2-([2,2'-bipyridin]-6-yl)-1,8-naphthyridine,记为Mn配合物2),这一结构模型可以作为自然界光系统Ⅱ中释氧中心复合物的仿生模型。密度泛函理论的计算结果表明,之前所提出的Mn配合物1催化剂分子可以通过引入一个含有效质子受体的配体,来对配体结构进行合理的设计。在水氧化反应中,使用Mn配合物2代替Mn配合物1作为催化剂时,O-O键形成时所对应的反应能垒会大幅降低。与此同时,这样的结构变化并不会引入明显的空间位阻效应。这项研究工作为实验上设计出有效的水氧化催化剂提供了重要的启示,也对理解光系统Ⅱ中氧气释放的反应机理提供了一定的线索。以上研究从双核锰基水氧化催化剂的微观反应机制入手,通过密度泛函理论的计算手段,深度分析了催化剂分子的结构与性质问的关联性,通过对催化剂的配体结构进行改造,提高了其催化性能,对于发展具有应用前景的人工光合作用体系具有重要价值。
[Abstract]:Artificial photosynthesis system, using hydrogen water with solar energy, is to realize the conversion of solar energy into chemical energy is clean, an ideal method to solve the social environment pollution and energy crisis. In the design of artificial photosynthetic systems, water oxidation as a source of electron and proton artificial photosynthesis system, is restricted the key factors of solar energy conversion. Therefore, the development of catalysts for the oxidation of water to achieve stable and efficient conversion of solar energy is very important. In many water oxidation catalysts, manganese based catalyst because of its nature and photosynthetic transition metals (MN) consistent system, have received particular attention.
Thanks to the rapid development of quantum chemistry calculation method and high performance computing capacity, based on the density functional theory (Density Functional Theory, DFT) plays an increasingly important role in the prediction analysis and chemical properties of the first principle calculation method in the molecular reaction mechanism. This paper from density functional theory calculations based on bionics the binuclear manganese based catalysts for the oxidation of water as the starting point, space and electronic structure properties of this catalyst, were systematically investigated and the catalytic water oxidation reaction mechanism; on this basis, based on binuclear manganese based water oxidation catalyst further understanding of ligand structure on catalyst molecule transformation, from the theoretical design it has a higher catalytic efficiency of dinuclear manganese based water oxidation catalyst.
There are four chapters in this thesis. This paper introduces the research background and on the basis of the first chapter. From the plant photosynthesis of photosystem II, introduces the composition of artificial photosynthesis system, the sensitizer involved from the artificial photosynthesis system, proton reduction catalyst and critical water oxygen catalytic reaction is introduced to expand. Water oxidation, catalytic water oxidation catalyst from the evaluation ability, elaborates the mechanism analysis angle of molecular water oxidation catalyst. Then introduces the molecular water oxidation catalyst widely studied in the literature. Finally briefly calculated density functional theory, we adopt the method.
In the second chapter, we introduced the research object of this paper a binuclear manganese based water oxidation catalyst [H2O (terpy) Mn (-O) 2Mn (terpy) OH2]3+ (terpy=2,2': 6', 2 "-terpyridine, denoted as Mn complex 1) the progress of experimental and theoretical studies, and gives the structure analysis about 1 of the Mn complexes and the related calculation details.
In the third chapter, we use density functional method to investigate the asymmetry of two manganese ions existing in the center of the geometric and electronic structure, and the impact of asymmetric chemical properties. In this study, we calculated the Mn complex 1 in acetic acid buffer solution in a stable configuration, and the asymmetry of two manganese ion center from the two angles of thermodynamics and dynamics are analyzed in detail. Through the study found that, because the tetravalent manganese ion center has greater steric effects, is not conducive to the combination of acetate ions, lead acetate ions mainly with trivalent manganese ions in the center, which clarified the differences on acetate ions the binding sites in the literature.
In the fourth chapter, we take the Mn complex reaction mechanism of 1 catalytic water oxidation based on the transformation of this catalyst ligand structure, and designs a new dinuclear manganese based catalyst [H2O (2-bpNP) Mn (-O) 2Mn (2-bpNP) OH2]3+ (2-bpNP=2- (-1,8-naphthyridine [2,2'-bipyridin]-6-yl), denoted as 2) Mn complexes, a bionic model of this model can be used as a natural oxygen evolving center in photosystem II complexes. DFT calculation results show that the proposed Mn complexes 1 catalyst molecules can pass into an effective proton containing receptor ligands, to carry on the reasonable design of the ligand structure. In the water oxidation reaction, using Mn complex 2 instead of Mn 1 complexes as catalysts, the reaction barrier will significantly reduce the formation of O-O bond. At the same time, such a structural change and will not bring obvious space Steric hindrance effect. This research provides important inspiration for designing effective catalysts for water oxidation in experiment, and also provides some clues for understanding the mechanism of oxygen release in photosystem II.
The above research will start from the micro reaction mechanism of dinuclear manganese based water oxidation catalyst, the calculation method of density functional theory, in-depth analysis of the relationship between the structure and properties of catalyst molecules asked, by modifying the ligand structure on the catalyst, improving its catalytic performance, has the application prospect for the development of the artificial photosynthesis system has important value.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：O643.31;TQ116.2

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