Understanding THz Spectra of Aqueous Solutions: Glycine in Light and Heavy Water
Understanding THz Spectra of Aqueous Solutions: Glycine in Light and Heavy Water
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DOI：
10.1021/ja4129857
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发表时间：
2014-04-02
影响因子：
15
通讯作者：
Havenith, Martina
中科院分区：
文献类型：
--
作者：
Sun, Jian;Niehues, Gudrun;Havenith, Martina
水溶液的太赫兹光谱最近被建立为一种有价值的和互补的实验工具，可以直接了解由于涉及界面水的氢键动力学引起的溶质-溶剂耦合。尽管实验取得了很大进展，但从分子运动的角度理解太赫兹光谱，类似于中红外光谱，仍然是难以捉摸的。在这里，以渗透保护剂甘氨酸为例，我们展示了如何通过结合太赫兹吸收光谱和从头算分子动力学来实现这一目标。实验太赫兹光谱的特点是宽而清晰可辨的峰。基于现有模式特定分解方案的大量扩展，实验光谱可以通过理论再现，并在本质上定量分配。这一共同努力揭示了分子运动对太赫兹吸收光谱的独特贡献，其独特模式源于分子内振动、刚体样受阻旋转和平移运动，以及与界面水分子的特定耦合。在重水中氘化甘氨酸的太赫兹光谱中观察到的峰移证实了这一分配，这使我们能够在实验中分离出不同的模式。
THz spectroscopy of aqueous solutions has been established as of recently to be a valuable and complementary experimental tool to provide direct insights into the solute-solvent coupling due to hydrogen-bond dynamics involving interfacial water. Despite much experimental progress, understanding THz spectra in terms of molecular motions, akin to midinfrared spectra, still remains elusive. Here, using the osmoprotectant glycine as a showcase, we demonstrate how this can be achieved by combining THz absorption spectroscopy and ab initio molecular dynamics. The experimental THz spectrum is characterized by broad yet clearly discernible peaks. Based on substantial extensions of available mode-specific decomposition schemes, the experimental spectrum can be reproduced by theory and assigned on an essentially quantitative level. This joint effort reveals an unexpectedly clear picture of the individual contributions of molecular motion to the THz absorption spectrum in terms of distinct modes stemming from intramolecular vibrations, rigid-body-like hindered rotational and translational motion, and specific couplings to interfacial water molecules. The assignment is confirmed by the peak shifts observed in the THz spectrum of deuterated glycine in heavy water, which allow us to separate the distinct modes experimentally.