Dissecting the THz spectrum of liquid water from first principles via correlations in time and space
Dissecting the THz spectrum of liquid water from first principles via correlations in time and space
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DOI：
10.1073/pnas.0914885107
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发表时间：
2010-07-06
影响因子：
11.1
通讯作者：
Marx, Dominik
中科院分区：
文献类型：
--
作者：
Heyden, Matthias;Sun, Jian;Marx, Dominik
分子在水中的溶剂化是无数分子现象的核心，对于理解化学反应性或生物分子功能等不同问题至关重要。补充完善的方法，它已被证明，在太赫兹频域的激光光谱提供了新的见解，从小溶质到蛋白质的水化。在引入空间分辨分析的吸收截面的模拟，太赫兹光谱的灵敏度追溯到特征的距离依赖性调制散装水的吸收强度。在约200 cm（-1）处的显著峰由第一壳层动力学主导，而涉及第二溶剂化壳层的协同运动对约80 cm（-1）处的吸收贡献最大，接近2.4 THz。后者可以理解为两个氢键四面体沿着连接氢键轴的伞状运动。因此，氢键网络的修饰，e.例如，在一个实施例中，由于溶质的存在，预期至少在对应于两层溶剂化水分子的长度尺度上影响振动运动和THz吸收强度。这一结果提供了一个分子机制，解释实验确定的吸收变化的灵敏度在太赫兹域中的不同，溶质诱导的动力学性质的溶剂化壳（生物）分子，即使在没有明确定义的共振。
Solvation of molecules in water is at the heart of a myriad of molecular phenomena and of crucial importance to understanding such diverse issues as chemical reactivity or biomolecular function. Complementing well-established approaches, it has been shown that laser spectroscopy in the THz frequency domain offers new insights into hydration from small solutes to proteins. Upon introducing spatially-resolved analyses of the absorption cross section by simulations, the sensitivity of THz spectroscopy is traced back to characteristic distance-dependent modulations of absorption intensities for bulk water. The prominent peak at approximate to 200 cm(-1) is dominated by first-shell dynamics, whereas a concerted motion involving the second solvation shell contributes most significantly to the absorption at about 80 cm(-1) approximate to 2.4 THz. The latter can be understood in terms of an umbrella-like motion of two hydrogen-bonded tetrahedra along the connecting hydrogen bond axis. Thus, a modification of the hydrogen bond network, e. g., due to the presence of a solute, is expected to affect vibrational motion and THz absorption intensity at least on a length scale that corresponds to two layers of solvating water molecules. This result provides a molecular mechanism explaining the experimentally determined sensitivity of absorption changes in the THz domain in terms of distinct, solute-induced dynamical properties in solvation shells of (bio)molecules-even in the absence of well-defined resonances.