水团簇中氢键的电子结构理论研究
发布时间：2018-09-18 21:07
【摘要】：水是自然界中广泛分布的物质,其参与众多的物理、化学过程,并为生化反应等提供基本的环境。从原子水平认识水体系的存在形式、性质及行为对于从本质上理解相关领域的基本问题意义重大。水的微观形态可被一般性的看作是由水分子通过分子间氢键相互作用彼此聚集而形成的氢键网络体系,而不同尺寸的水团簇即是氢键网络的基本单元。水团簇的结构自由度及氢键网络的复杂行为使得微观水体系的性质不止局限于水分子自身的属性,而同时可以体现出团簇结构随尺寸和对称性的演化特性,以及通过氢键网络实现的构象转变、质子转移等过程。水分子间的氢键决定了氢键体系的结构属性并与水分子自身的电子结构密切相关,近年的实验观测更表明分子间氢键具有与共价键类似的电子结构,这暗示从电子结构角度出发针对水团簇体系进行系统性的理论研究可能为上述水氢键体系的性质与行为提供基础层次的理解。同时,水氢键体系的质子转移问题在各学科及相互间兴趣交叉的研究领域,也占有重要位置。本文使用量子力学第一性原理方法,从电子结构角度出发报道了对水团簇进行的系统性研究。我们分别阐述了水分子间氢键类共价特性的分子轨道表现、小尺寸环状水团簇的离域电子结构特性、环状水团簇中离域分子轨道与其几何结构平面化间的关联、水团簇中心四配位水分子的四氢键电子结构在中等尺寸水团簇中随尺寸变化的趋势,以及棱柱水团簇协同质子转移过程中的手性转变与识别这五个方面的内容。首先,我们选取水二聚物(H2O)2这一基本模型应用高精度第一性原理计算方法,从分子轨道角度出发研究了水分子间氢键的类共价特性。分子轨道分析发现了两条贯穿氢键区域的分子轨道,其贡献主要来自于氢键供体一侧的氧原子2p轨道。进一步的能量分解分析表明两个水分子之间存在不可忽略的诱导作用,其在两水分子相互作用能总吸引项中的比例高于10%,这进一步支持了氢键的类共价特性。这一研究对理解冰、液态水、功能化材料以及生物系统中的氢键相互作用提供了新的分子轨道视角,并为本文基于电子结构来研究水团簇及氢键网络提供了基础指引。第二,准平面小水环(H2O)n(n=3-6)是构成更为复杂三维水团簇和液态水模型的的基本结构和功能单元,进一步理解分子间氢键相互作用在其中的特点对于认识复杂水团簇及氢键网络的性质具有基础性意义。我们应用密度泛函理论结合键特性分析方法,研究了这类小尺寸环状水团簇,结果表明n=3和4的两种小水环均出现离域于整个环并覆盖环中心区域的离域分子轨道,其贡献来自于各个水分子的氢氧原子,而在n=5和6的水环中相应离域轨道在环中心区域的轨道分布减弱。环状水团簇中的离域电子结构扩展了对水团簇中分子间氢键的认识,其展示的分子间氢键电子结构与体系几何结构间的相互影响及其随尺寸变化的特性为后续工作提供了指引。第三,承接上一研究,我们继续探索了n=3-6的小尺寸环状水团簇(H2O)n中离域电子结构与其几何结构平面化之间的联系。结果表明离域于水环氢键骨架中的三种离域分子轨道与体系能否形成稳定的平面结构密切相关,它们分别为轨道(Ⅰ),主要由氧原子的孤对电子轨道O(2p)组成的分子轨道;轨道(Ⅱ),主要由O(2p)-H(1s)形成的沿氢键方向的成键轨道;以及轨道(Ⅲ),主要由O(2s)-H(1s)形成的成键轨道。当水环几何结构为平面结构时,利于水分子单体轨道之间针对这三种离域轨道实现彼此重叠最大化。进一步的能量分解分析显示,在所有的水环中轨道项的贡献在相互作用能总吸引项中的比例多于30%,这再一次凸显了氢键系统的类共价特性。第四,基于对小尺寸水团簇的基本认识及研究中体现出的氢键电子结构随尺寸变化的规律,同时面向水团簇作为液态水静态模型时需要考虑的尺寸效应等问题,我们研究了接近液态水中水分子性质的4-配位水分子在团簇(H2O)n(n=17,19,20,21,23,25)中形成的四氢键电子结构,随团簇尺寸变化的趋势。结果表明,中心4-配位水分子与其最近邻水分子之间的相互作用随着团簇水分子数增多而减弱,中心4-配位水分子与次近邻水分子之间的相互作用能随着水分子数目的增多而增强。这表明中心4-配位水分子同最近邻和次近邻水分子之间的相互作用存在竞争关系。而光谱和电子密度分析表明中心水分子参与的最低频分子间振动与其和水笼之间的电子得失没有明显的尺寸依赖变化。此外,中心4-配位水分子四氢键电子结构的类共价特性被拓扑分析进一步阐明。我们希望这一理论研究能够为中等尺寸水团簇的研究及理解液态水中的氢键相互作用提供基本的理论参考。最后,基于以上基础认识,我们进一步探究了氢键网络中的动态过程。沿氢键的质子转移和手性转换过程是物理学及其与生命科学、材料科学等学科交叉领域的基本问题。其在手性识别、酶催化和药物制备等化工生产方面也具有重要意义。在本部分工作中,我们在理论上研究了可看作双层水环的小棱柱水团簇中单层内质子协同转移过程的手性转换和识别问题。结果表明,虽然质子转移初末态的能量变化很小,仅约为0.3 kcal/mol,但是振动圆二色谱(VCD)却提供了一个明显的手性特征峰区域(3000~3500 cm-1),可以用来区别具有手性特征的初末态水团簇结构。这个区域的振动模式对应于层内氢键的拉伸,而且该区域的振动模式在红外和拉曼光谱中也具有易于观测的较强信号。另外,电子圆二色性谱(ECD)也展示了类似的识别特性。进一步的分子轨道分析显示,涉及两层间相互作用的轨道主要源于氧原子的2p轨道,并且层内协同质子转移过程可使相应层间轨道的能级抬升0.1 e V。此外,我们的研究还发现,氘原子的同位素取代能够在VCD谱上引起明显的特征峰移动,进而为可能的水团簇手性识别的实验探测提供了原理性设计思路。希望我们的发现能够在原子水平上为水团簇手性概念的夯实,乃至手性识别观测在相应实验过程中的实现起到促进作用。
[Abstract]:Water is a widely distributed substance in nature. It participates in many physical and chemical processes and provides a basic environment for biochemical reactions. It is of great significance to understand the existence form, nature and behavior of water system at the atomic level for understanding the basic problems in related fields in essence. The micro-morphology of water can be generally regarded as water. Hydrogen bond networks formed by the aggregation of molecules through hydrogen bond interactions are the basic units of hydrogen bond networks. The structural degrees of freedom of water clusters and the complex behavior of hydrogen bond networks make the properties of micro-water systems not only confined to the properties of water molecules, but also embody the properties of water clusters. The evolution of cluster structure with size and symmetry, as well as the conformational transition and proton transfer through hydrogen bonding networks. The hydrogen bonding between water molecules determines the structural properties of the hydrogen bonding system and is closely related to the electronic structure of the water molecule itself. This implies that a systematic theoretical study of water clusters from the viewpoint of electronic structure may provide a fundamental understanding of the properties and behaviors of the above-mentioned water-hydrogen bonding systems. The first-principles method of quantum mechanics reports the systematic study of water clusters from the point of view of electronic structure. The molecular orbital representations of the covalent properties of hydrogen bonds between water molecules, the characteristics of the off-domain electronic structure of small-sized ring water clusters, and the planarization of the off-domain molecular orbitals and their geometric structures in ring water clusters are described. The relationship between the four-hydrogen bond electronic structures of the four-coordinated water molecules in the center of a water cluster and the size-dependent trend of the four-hydrogen bond electronic structures in a medium-sized water cluster, as well as the chiral transition and recognition in the process of the prismatic water cluster cooperating with the proton transfer, are discussed. Firstly, we select the water dimer (H2O) 2 as the basic model to apply the high-precision first property. The molecular orbital analysis reveals that two molecular orbitals penetrate the hydrogen bond region and their contributions mainly come from the 2p orbital of the oxygen atom on the donor side of the hydrogen bond. This study provides a new molecular orbital perspective for understanding the interaction of hydrogen bonds in ice, liquid water, functionalized materials and biological systems, and for studying water based on electronic structure. Clusters and hydrogen-bonded networks provide basic guidance. Second, quasi-planar small water rings (H2O) n (n=3-6) are the basic structure and functional units of more complex three-dimensional water clusters and liquid water models. Further understanding the characteristics of hydrogen-bonded interactions among molecules is fundamental for understanding the properties of complex water clusters and hydrogen-bonded networks. The results show that both n=3 and 4 small water rings have delocalized molecular orbitals which are located in the whole ring and cover the central region of the ring. The contribution comes from the hydrogen and oxygen atoms of each water molecule, while the corresponding delocalization occurs in the water rings of n=5 and 6. The orbital distribution in the central region of the ring decreases. The detached electronic structure of the water cluster expands the understanding of the hydrogen bonds between molecules in the water cluster. The interaction between the electronic structure of the hydrogen bond and the geometric structure of the system and its size-dependent characteristics provide guidance for the follow-up work. We continue to explore the relationship between the delocalized electronic structure and the planarization of the geometric structure of the small annular water cluster (H2O) n with n=3-6. The results show that the three delocalized molecular orbitals in the hydrogen-bonded skeleton of the water ring are closely related to the formation of stable planar structures of the system, which are orbitals (I) and are mainly solitary oxygen atoms. Molecular orbitals consisting of O (2p), O (2p) - H (1s) and O (2s) - H (1s) are the main bonding orbitals, and the bonding orbitals (III) consisting mainly of O (2s) - H (1s) are the main ones. When the geometric structure of the water ring is planar, it is advantageous to achieve the maximum overlap among the three kinds of detached orbits. Further energy decomposition analysis shows that the contribution of the orbital term to the total attraction of the interaction energy is more than 30% in all water rings, which again highlights the covalent-like properties of hydrogen bonding systems. Fourthly, based on the basic understanding of small water clusters and the size-dependent variation of the electronic structure of hydrogen bonding in the study. At the same time, for the size effect of water cluster as a static model of liquid water, we studied the electronic structure of four-hydrogen bond formed in clusters (H2O) n (n = 17, 19, 20, 21, 23, 25) by 4-coordinated water molecules close to the properties of water molecules in liquid water. The interaction between the nearest neighbor water molecules decreases with the increase of the number of cluster water molecules, and the interaction between the center 4-coordination water molecules and the next nearest neighbor water molecules increases with the increase of the number of water molecules. Spectroscopic and electron density analyses show that there is no significant size-dependent change in the lowest frequency intermolecular vibrations of the central water molecule and the electron gain and loss between the central water molecule and the water cage. In addition, the covalent-like properties of the electronic structure of the tetrahydrogen bond of the central 4-coordination water molecule are further elucidated by topological analysis. Finally, based on the above basic knowledge, we further explore the dynamic process of hydrogen bond network. Proton transfer and chiral transition along hydrogen bond are the basic fields of physics, life science and material science. In this part, we theoretically study the chiral transformation and recognition of proton synergistic transfer in a small prismatic water cluster, which can be regarded as a double-layer water ring. The results show that although the initial and final states of proton transfer are energetic, the chiral transformation and recognition of proton synergistic transfer in a single-layer water cluster are also important. However, vibrational circular dichroism (VCD) provides a distinct chiral peak region (3000-3500 cm-1) that can be used to distinguish the initial and final water clusters with chiral characteristics. In addition, electron circular dichroism spectroscopy (ECD) shows similar recognition properties. Further molecular orbital analysis shows that the orbits involved in the interaction between the two layers are mainly derived from the 2p orbits of the oxygen atoms, and that the energy levels of the corresponding interlayer orbits can be raised by 0. 1 e V. In addition, we also found that the isotope substitution of deuterium atoms can cause significant characteristic peak shifts in VCD spectra, which provides a theoretical design for the possible experimental detection of chiral recognition of water clusters. Measurement plays an important role in the realization of corresponding experiments.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O562
，
本文编号：2249103
[Abstract]:Water is a widely distributed substance in nature. It participates in many physical and chemical processes and provides a basic environment for biochemical reactions. It is of great significance to understand the existence form, nature and behavior of water system at the atomic level for understanding the basic problems in related fields in essence. The micro-morphology of water can be generally regarded as water. Hydrogen bond networks formed by the aggregation of molecules through hydrogen bond interactions are the basic units of hydrogen bond networks. The structural degrees of freedom of water clusters and the complex behavior of hydrogen bond networks make the properties of micro-water systems not only confined to the properties of water molecules, but also embody the properties of water clusters. The evolution of cluster structure with size and symmetry, as well as the conformational transition and proton transfer through hydrogen bonding networks. The hydrogen bonding between water molecules determines the structural properties of the hydrogen bonding system and is closely related to the electronic structure of the water molecule itself. This implies that a systematic theoretical study of water clusters from the viewpoint of electronic structure may provide a fundamental understanding of the properties and behaviors of the above-mentioned water-hydrogen bonding systems. The first-principles method of quantum mechanics reports the systematic study of water clusters from the point of view of electronic structure. The molecular orbital representations of the covalent properties of hydrogen bonds between water molecules, the characteristics of the off-domain electronic structure of small-sized ring water clusters, and the planarization of the off-domain molecular orbitals and their geometric structures in ring water clusters are described. The relationship between the four-hydrogen bond electronic structures of the four-coordinated water molecules in the center of a water cluster and the size-dependent trend of the four-hydrogen bond electronic structures in a medium-sized water cluster, as well as the chiral transition and recognition in the process of the prismatic water cluster cooperating with the proton transfer, are discussed. Firstly, we select the water dimer (H2O) 2 as the basic model to apply the high-precision first property. The molecular orbital analysis reveals that two molecular orbitals penetrate the hydrogen bond region and their contributions mainly come from the 2p orbital of the oxygen atom on the donor side of the hydrogen bond. This study provides a new molecular orbital perspective for understanding the interaction of hydrogen bonds in ice, liquid water, functionalized materials and biological systems, and for studying water based on electronic structure. Clusters and hydrogen-bonded networks provide basic guidance. Second, quasi-planar small water rings (H2O) n (n=3-6) are the basic structure and functional units of more complex three-dimensional water clusters and liquid water models. Further understanding the characteristics of hydrogen-bonded interactions among molecules is fundamental for understanding the properties of complex water clusters and hydrogen-bonded networks. The results show that both n=3 and 4 small water rings have delocalized molecular orbitals which are located in the whole ring and cover the central region of the ring. The contribution comes from the hydrogen and oxygen atoms of each water molecule, while the corresponding delocalization occurs in the water rings of n=5 and 6. The orbital distribution in the central region of the ring decreases. The detached electronic structure of the water cluster expands the understanding of the hydrogen bonds between molecules in the water cluster. The interaction between the electronic structure of the hydrogen bond and the geometric structure of the system and its size-dependent characteristics provide guidance for the follow-up work. We continue to explore the relationship between the delocalized electronic structure and the planarization of the geometric structure of the small annular water cluster (H2O) n with n=3-6. The results show that the three delocalized molecular orbitals in the hydrogen-bonded skeleton of the water ring are closely related to the formation of stable planar structures of the system, which are orbitals (I) and are mainly solitary oxygen atoms. Molecular orbitals consisting of O (2p), O (2p) - H (1s) and O (2s) - H (1s) are the main bonding orbitals, and the bonding orbitals (III) consisting mainly of O (2s) - H (1s) are the main ones. When the geometric structure of the water ring is planar, it is advantageous to achieve the maximum overlap among the three kinds of detached orbits. Further energy decomposition analysis shows that the contribution of the orbital term to the total attraction of the interaction energy is more than 30% in all water rings, which again highlights the covalent-like properties of hydrogen bonding systems. Fourthly, based on the basic understanding of small water clusters and the size-dependent variation of the electronic structure of hydrogen bonding in the study. At the same time, for the size effect of water cluster as a static model of liquid water, we studied the electronic structure of four-hydrogen bond formed in clusters (H2O) n (n = 17, 19, 20, 21, 23, 25) by 4-coordinated water molecules close to the properties of water molecules in liquid water. The interaction between the nearest neighbor water molecules decreases with the increase of the number of cluster water molecules, and the interaction between the center 4-coordination water molecules and the next nearest neighbor water molecules increases with the increase of the number of water molecules. Spectroscopic and electron density analyses show that there is no significant size-dependent change in the lowest frequency intermolecular vibrations of the central water molecule and the electron gain and loss between the central water molecule and the water cage. In addition, the covalent-like properties of the electronic structure of the tetrahydrogen bond of the central 4-coordination water molecule are further elucidated by topological analysis. Finally, based on the above basic knowledge, we further explore the dynamic process of hydrogen bond network. Proton transfer and chiral transition along hydrogen bond are the basic fields of physics, life science and material science. In this part, we theoretically study the chiral transformation and recognition of proton synergistic transfer in a small prismatic water cluster, which can be regarded as a double-layer water ring. The results show that although the initial and final states of proton transfer are energetic, the chiral transformation and recognition of proton synergistic transfer in a single-layer water cluster are also important. However, vibrational circular dichroism (VCD) provides a distinct chiral peak region (3000-3500 cm-1) that can be used to distinguish the initial and final water clusters with chiral characteristics. In addition, electron circular dichroism spectroscopy (ECD) shows similar recognition properties. Further molecular orbital analysis shows that the orbits involved in the interaction between the two layers are mainly derived from the 2p orbits of the oxygen atoms, and that the energy levels of the corresponding interlayer orbits can be raised by 0. 1 e V. In addition, we also found that the isotope substitution of deuterium atoms can cause significant characteristic peak shifts in VCD spectra, which provides a theoretical design for the possible experimental detection of chiral recognition of water clusters. Measurement plays an important role in the realization of corresponding experiments.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O562
，
本文编号：2249103
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