Charge Asymmetry at Aqueous Hydrophobic Interfaces and Hydration Shells
Charge Asymmetry at Aqueous Hydrophobic Interfaces and Hydration Shells
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DOI：
10.1002/anie.201310266
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发表时间：
2014-09-01
影响因子：
16.6
通讯作者：
Roke, Sylvie
中科院分区：
文献类型：
--
作者：
Scheu, Ruediger;Rankin, Blake M.;Roke, Sylvie
介电连续体中离子的溶剂化与离子电荷的符号是对称的。然而，许多现象显示了间接证据表明水可能对负电荷有偏好：绝大多数生物膜界面是中性或带负电荷的，（[1]）阴离子和阳离子周围的水重定向动力学是不同的，（[2]）水的零电荷点通常远低于pH 7在疏水/水界面。毫无疑问，这与水分子的不对称性有关。在这里，我们用光谱量化了水合壳和疏水/水界面结构之间的差异，这些结构是由电荷相反但分子结构基本相同的离子引起的。研究表明，四苯基硼酸盐（TPB+）和四苯基拉森离子（TPA(+)）与水及其界面的相互作用显著不同：阴离子优先水化，并在疏水界面附近诱导更大的取向顺序。相反，阳离子形成的pi-H键比阴离子少得多，也弱得多，并且在疏水界面附近强烈地降低了水的取向顺序。
The solvation of ions in a dielectric continuum is symmetric with respect to the sign of the ionic charge. Yet, many phenomena show indirect evidence that water may have a preference for negative charge: the vast majority of biological membrane interfaces are neutral or negatively charged,([1]) water reorientation dynamics around anions and cations is different,([2]) and the zero charge point of water is usually well below pH 7 at hydrophobic/water interfaces.([3]) There is undoubtedly a link to the asymmetry of the water molecule. Here, we spectroscopically quantify differences between the structures of hydration shells and hydrophobic/water interfaces induced by ions of opposite charge but essentially identical molecular structure. We show that these two ions, tetraphenylborate (TPB+) and tetraphenylarsonium (TPA(+)), interact dramatically differently with water and its interface: The anion is preferentially hydrated and induces greater orientational order to water near hydrophobic interfaces. In contrast, the cation forms far fewer and weaker pi-H bonds than the anion and strongly reduces the orientational order of water near a hydrophobic interface.