Purdue University, Department of Chemistry, West Lafayette, Indiana 47907, USA.
Nat Chem. 2013 Sep;5(9):796-802. doi: 10.1038/nchem.1716. Epub 2013 Jul 21.
The unique structural, dynamical and chemical properties of air/water and oil/water interfaces are thought to play a key role in various biological, geological and environmental processes. For example, non-hydrogen-bonded ('dangling') OH groups--which create surface defects in water's hydrogen bonding network and are experimentally detected at both macroscopic (air/water or oil/water) and microscopic (dissolved hydrophobic molecule) interfaces--are thought to catalyse some chemical reactions. However, how the size, curvature or charge of the exposed hydrophobic surface influences water's propensity to form dangling OH defects has not yet been established quantitatively. Here we use Raman multivariate curve resolution to probe spectroscopically the hydrophobic hydration shell and, using a statistical multisite analysis, we show that such interfacial dangling OH structures are entropically stabilized and their formation is cooperative (the probability that a non-hydrogen-bonded OH group will form depends nonlinearly on the hydrophobic surface area). We thus expose an important difference between the chemical properties of molecular and macroscopic oil/water interfaces.
空气/水和油/水界面独特的结构、动力学和化学性质被认为在各种生物、地质和环境过程中起着关键作用。例如，非氢键合（“悬空”）的 OH 基团——在水的氢键网络中形成表面缺陷，并且在宏观（空气/水或油/水）和微观（溶解的疏水分子）界面上都有实验检测到——被认为可以催化一些化学反应。然而，暴露的疏水面的大小、曲率或电荷如何影响水形成悬空 OH 缺陷的倾向，尚未得到定量确定。在这里，我们使用拉曼多变量曲线解析来光谱探测疏水性水合壳，并且使用统计多站点分析，我们表明这种界面悬空 OH 结构是熵稳定的，并且它们的形成是协同的（非氢键合的 OH 基团形成的概率取决于疏水表面面积的非线性）。因此，我们揭示了分子和宏观油/水界面化学性质之间的一个重要区别。
