有机小分子水合层太赫兹光谱解析的理论研究

Hydration layer is directly involved in many biological reactions and biological processes, such as maintaining the activity of a protein, helping protein folding and proton transfer. The vibration of hydrogen bond network in water is among the frequency range of terahertz spectrum, thus, the terahertz spectroscopy is wildly used in studying the dynamics of hydration water. While, the hydration layer and bulk water is identical in chemical components, the difference of dynamics in hydration layer is come from the interaction between solute molecules and water molecules. The terahertz spectrum of hydration layers need to be extracted from the THz signals of solution based on theoretical models. The theoretical analysis model assumes that the hydration layer is a continuous media, which has uniform thickness and terahertz absorption. And the interaction of the hydrated layer and bulk water is ignored. This project will study the physical mechanics of hydration layer, by simulating a series of small organic molecules in solutions with different molecular dipole, based on molecular dynamics simulation. We will study the effect of different interaction between small molecules and water molecules in hydration layer. Our goal is to build a statistical model describing the non-uniform hydration layer, and testified by comparing theoretical and experimental results. We hope this study will provide a theoretical basis for research THz spectrum of hydration layers around biomolecules.

水合层直接参与了许多生物反应和生物过程，如，维持蛋白质活性，帮助蛋白质折叠，参与质子传输等，具有重要的生物学意义。水中氢键网络的振动频率位于太赫兹波的频谱范围内，使得太赫兹光谱成为观测水以及水合层最直接的实验手段。水合层是由受到溶质影响的水形成的，不能单独存在。其太赫兹信号需要根据理论模型从溶液的信号中解析出来。目前理论解析模型中假设水合层是连续介质，具有均匀的厚度和均一的太赫兹响应，同时忽略了水合层与体相水的相互作用。本项目将通过分子动力学模拟研究水合层形成的物理机制，分析有机小分子与水之间的相互作用对水合层的影响，研究有机小分子水合层在不同溶液环境下的特性，寻找能够区分水合层与体相水对太赫兹响应的物理量，并将该物理量引入到太赫兹理论分析模型中，为生物分子水合层的太赫兹谱解谱研究提供理论基础。

水合水对于理解生物学过程至关重要。随着硬件的发展，太赫兹（THz）的介电弛豫谱已成为研究水化水的有力工具。但是，现有模型提取的水化水的太赫兹信号对于忽略溶液中各组分之间的相互作用是不可靠的。在这里，我们提出了一个新的模型，即溶液的太赫兹响应是体积分数单分子太赫兹响应的总和，它是由分子偶极自相关和分子偶极与周围环境的相关性决定的。因此，由于偶极与周围环境的相关性，水化水与散装水是有区别的。实验和分子动力学模拟结果证明了我们对1,4-二恶烷水溶液的理论预测，并从中提取了水合水的THz光谱。我们的模型提供了对溶液中介电响应的正确物理理解，并将提高对水合水的特殊作用的理解。

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