Anomalous dielectric relaxation of water molecules at the surface of an aqueous micelle
Anomalous dielectric relaxation of water molecules at the surface of an aqueous micelle
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DOI：
10.1063/1.1635803
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发表时间：
2004-01-22
影响因子：
4.4
通讯作者：
Bagchi, B
中科院分区：
文献类型：
--
作者：
Pal, S;Balasubramanian, S;Bagchi, B
胶束、蛋白质和许多复杂系统的水溶液的介电弛豫在对应于本体水的旋转运动和有组织的组装体或大分子的旋转运动的频率之间的中间频率处显示出异常分散。这种反常色散的确切起源还不清楚。在这项工作中，我们采用大规模的原子分子动力学模拟研究的介电弛豫（DR）的水分子在水胶束溶液的十五溴辛酸铯。模拟清楚地显示了水分子的矩-矩时间相关函数[Phi（M）（W）（t）]中存在慢分量，其时间常数约为40 ps，而散装水的时间常数仅为9 ps。有趣的是，在表面的单个水分子的取向时间相关函数[C-mu（t）]表现出一个组件的时间常数约为19 ps。我们表明，这两个时间常数可以由著名的统计力学的微观宏观关系。此外，表面水分子的重新取向表现出一个非常缓慢的组件，衰减的时间常数约为500 ps。氢键寿命和旋转松弛的胶束体上固定的坐标系中的分析似乎表明，500 ps组件欠其起源的水分子在表面上的扩展氢键网络的存在。然而，这个超低分量是没有发现在总的时刻时刻的时间相关函数的水分子在溶液中。水合水的缓慢DR被发现与铯离子在水-胶束界面的缓慢溶剂化动力学有很好的相关性。(C)2004年，美国物理学会。
Dielectric relaxation of aqueous solutions of micelles, proteins, and many complex systems shows an anomalous dispersion at frequencies intermediate between those corresponding to the rotational motion of bulk water and that of the organized assembly or macromolecule. The precise origin of this anomalous dispersion is not well-understood. In this work we employ large scale atomistic molecular dynamics simulations to investigate the dielectric relaxation (DR) of water molecules in an aqueous micellar solution of cesium pentadecafluorooctanoate. The simulations clearly show the presence of a slow component in the moment-moment time correlation function [Phi(M)(W)(t)] of water molecules, with a time constant of about 40 ps, in contrast to only 9 ps for bulk water. Interestingly, the orientational time correlation function [C-mu(t)] of individual water molecules at the surface exhibits a component with a time constant of about 19 ps. We show that these two time constants can be related by the well-known micro-macrorelations of statistical mechanics. In addition, the reorientation of surface water molecules exhibits a very slow component that decays with a time constant of about 500 ps. An analysis of hydrogen bond lifetime and of the rotational relaxation in the coordinate frame fixed on the micellar body seems to suggest that the 500 ps component owes its origin to the existence of an extended hydrogen bond network of water molecules at the surface. However, this ultraslow component is not found in the total moment-moment time correlation function of water molecules in the solution. The slow DR of hydration water is found to be well correlated with the slow solvation dynamics of cesium ions at the water-micelle interface. (C) 2004 American Institute of Physics.