Biswas Rajib, Bagchi Biman
J Phys Condens Matter. 2018 Jan 10;30(1):013001. doi: 10.1088/1361-648X/aa9b1d.
In nature, water is often found in contact with surfaces that are extended on the scale of molecule size but small on a macroscopic scale. Examples include lipid bilayers and reverse micelles as well as biomolecules like proteins, DNA and zeolites, to name a few. While the presence of surfaces and interfaces interrupts the continuous hydrogen bond network of liquid water, confinement on a mesoscopic scale introduces new features. Even when extended on a molecular scale, natural and biological surfaces often have features (like charge, hydrophobicity) that vary on the scale of the molecular diameter of water. As a result, many new and exotic features, which are not seen in the bulk, appear in the dynamics of water close to the surface. These different behaviors bear the signature of both water-surface interactions and of confinement. In other words, the altered properties are the result of the synergistic effects of surface-water interactions and confinement. Ultrafast spectroscopy, theoretical modeling and computer simulations together form powerful synergistic approaches towards an understanding of the properties of confined water in such systems as nanocavities, reverse micelles (RMs), water inside and outside biomolecules like proteins and DNA, and also between two hydrophobic walls. We shall review the experimental results and place them in the context of theory and simulations. For water confined within RMs, we discuss the possible interference effects propagating from opposite surfaces. Similar interference is found to give rise to an effective attractive force between two hydrophobic surfaces immersed and kept fixed at a separation of d, with the force showing an exponential dependence on this distance. For protein and DNA hydration, we shall examine a multitude of timescales that arise from frustration effects due to the inherent heterogeneity of these surfaces. We pay particular attention to the role of orientational correlations and modification of the same due to interaction with the surfaces.
在自然界中，水常常与在分子尺度上具有一定扩展性但宏观尺度上较小的表面接触。例如脂质双层、反胶束以及蛋白质、DNA和沸石等生物分子，仅举几例。虽然表面和界面的存在会中断液态水连续的氢键网络，但介观尺度上的受限会引入新的特性。即使在分子尺度上具有扩展性，天然和生物表面通常也具有在水分子直径尺度上变化的特征（如电荷、疏水性）。因此，许多在体相中看不到的新奇特性出现在靠近表面的水的动力学中。这些不同的行为带有水 - 表面相互作用和受限的特征。换句话说，性质的改变是表面 - 水相互作用和受限协同效应的结果。超快光谱学、理论建模和计算机模拟共同构成了强大的协同方法，有助于理解诸如纳米腔、反胶束（RM）、蛋白质和DNA等生物分子内外的水以及两个疏水壁之间受限水的性质。我们将回顾实验结果，并将其置于理论和模拟的背景下。对于限制在反胶束中的水，我们讨论了从相对表面传播的可能干涉效应。发现类似的干涉会在浸入并保持固定间距为d的两个疏水表面之间产生有效的吸引力，该力对该距离呈指数依赖关系。对于蛋白质和DNA的水合作用，我们将研究由于这些表面固有的不均匀性导致的受挫效应所产生的多种时间尺度。我们特别关注取向相关性的作用以及由于与表面相互作用而对其进行的修正。
