Water dynamics in salt solutions studied with ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy.
Water dynamics in salt solutions studied with ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy.
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用超快二维红外（2D IR）振动回声光谱研究研究的盐溶液中的水动力学。
DOI：
10.1021/ar900043h
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发表时间：
2009-09-15
影响因子：
18.3
通讯作者：
Park S
中科院分区：
文献类型：
--
作者：
Fayer MD;Moilanen DE;Wong D;Rosenfeld DE;Fenn EE;Park S
水在自然界中无处不在，但它很少以纯净水的形式存在。从海洋到生物，水分子与各种各样的溶解物种相互作用。这些物种中有许多是带电的。在海洋中，水与溶解的盐相互作用。在生物系统中，水与溶解的盐以及带电荷的氨基酸、膜的两性离子头部基团和其他携带电荷的生物基团相互作用。水由于其动态的氢键网络而在许多化学过程中起着核心作用。一个水分子最多可以形成四个氢键，形成一个近似四面体的排列。这些氢键在皮秒的时间尺度上不断被打破，新的氢键正在形成。水的氢键网络能够快速重新配置，使水能够适应和促进化学过程。因此，带电物种对水氢键动力学的影响是重要的。超快相干红外光谱的最新进展极大地扩展了我们对水动力学的理解。二维红外（2D IR）振动回波光谱提供了新的观测量，产生在热平衡条件下的基态电子态的分子的快速动力学的直接信息。2D IR振动回波类似于2D NMR，但在短许多数量级的时间尺度上操作。在二维红外振动回波实验中，三个红外脉冲被调谐到感兴趣的振动频率，在这种情况下是水的羟基伸缩模式的频率。前两个脉冲通过它们的振动频率“标记”初始分子结构。系统在第二和第三脉冲之间演化，第三脉冲激发振动回波脉冲的发射，这是信号。通过将振动回波脉冲与另一个脉冲（本机振荡器）组合来外差检测振动回波脉冲。外差检测提供相位和幅度信息，这两者对于执行将数据从时域转换为二维频域频谱的两个傅立叶变换都是必要的。一系列二维红外振动回波光谱的时间依赖性提供了系统动力学的直接信息。在这里，我们使用两种类型的二维红外振动回波实验来研究带电物种对水氢键动力学的影响。研究了NaBr和NaBF_4的溶液。使用振动回波测量光谱扩散和偏振选择性红外泵浦探测测量取向弛豫的溴化钠溶液的浓度的函数进行了研究。这两种类型的测量表明，随着盐浓度的增加，氢键网络结构的演变放缓。NaBF4研究使用振动回波化学交换光谱。在这些实验中，可以直接观察到水分子与其他水分子之间的氢键交换。结果表明，水与离子相互作用的氢键动力学比纯水慢，但减慢是三到四倍，而不是数量级。
Water is ubiquitous in nature, but it exists as pure water infrequently. From the ocean to biology, water molecules interact with a wide variety of dissolved species. Many of these species are charged. In the ocean, water interacts with dissolved salts. In biological systems, water interacts with dissolved salts as well as with charged amino acids, the zwitterionic head groups of membranes, and other biological groups that carry charges. Water plays a central role in vast number of chemical processes because of its dynamic hydrogen bond network. A water molecule can form up to four hydrogen bonds in an approximately tetrahedral arrangement. These hydrogen bonds are continually being broken and new bonds are being formed on a picosecond time scale. The ability of water’s hydrogen bond network to rapidly reconfigure enables water to accommodate and facilitate chemical processes. Therefore, the influence of charged species on water hydrogen bond dynamics is important. Recent advances in ultrafast coherent infrared spectroscopy have greatly expanded our understanding of water dynamics. Two dimensional infrared (2D IR) vibrational echo spectroscopy is providing new observables that yield direct information on the fast dynamics of molecules in their ground electronic state under thermal equilibrium conditions. 2D IR vibrational echoes are akin to 2D NMR but operate on time scales that are many orders of magnitude shorter. In a 2D IR vibrational echo experiment (see Conspectus figure), three IR pulses are tuned to the vibrational frequency of interest, which in this case is the frequency of the hydroxyl stretching mode of water. The first two pulses “label” the initial molecular structures by their vibrational frequencies. The system evolves between pulses two and three, and the third pulse stimulates the emission of the vibrational echo pulse, which is the signal. The vibrational echo pulse is heterodyne detected by combining it with another pulse, the local oscillator. Heterodyne detection provides phase and amplitude information, which are both necessary to perform the two Fourier transforms that take the data from the time domain to a two dimensional frequency domain spectrum. The time dependence of a series of 2D IR vibrational echo spectra provides direct information on system dynamics. Here we use two types of 2D IR vibrational echo experiments to examine the influence that charged species have on water hydrogen bond dynamics. Solutions of NaBr and NaBF4 are studied. The NaBr solutions are studied as a function of concentration using vibrational echo measurements of spectral diffusion and polarization selective IR pump-probe measurements of orientational relaxation. Both types of measurements show the slowing of hydrogen bond network structural evolution with increasing salt concentration. NaBF4 is studied using vibrational echo chemical exchange spectroscopy. In these experiments it is possible to directly observe the chemical exchange of water molecules switching their hydrogen bond partners between and other water molecules. The results demonstrate that water interacting with ions has slower hydrogen bond dynamics than pure water, but the slowing is a factor of three or four rather than orders of magnitude.
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影响因子：
56.9
作者：
Laage, D;Hynes, JT
通讯作者：
Hynes, JT
影响因子：
4.4
作者：
Asbury, JB;Steinel, T;Fayer, MD
通讯作者：
Fayer, MD
影响因子：
4.4
作者：
Lawrence, CP;Skinner, JL
通讯作者：
Skinner, JL
影响因子：
4
作者：
SHIMIZU, A;TANIGUCHI, Y
通讯作者：
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影响因子：
3.3
作者：
Kwak, Kyungwon;Rosenfeld, Daniel E.;Chung, Jean K.;Fayer, Michael D.
通讯作者：
Fayer, Michael D.