Petersen Matt K, Hatt Alison J, Voth Gregory A
Department of Chemistry and Center for Biophysical Modeling and Simulation, University of Utah, Salt Lake City, UT 84112-0850, USA.
J Phys Chem B. 2008 Jul 3;112(26):7754-61. doi: 10.1021/jp800221x. Epub 2008 Jun 6.
Orientational anisotropies are calculated from molecular dynamics simulations of bulk water and the Na(+) and H(+) forms of hydrated Nafion and then compared with corresponding experimental values. The extended jump model of Laage and Hynes is applied to water reorientations for each system, and the anisotropies are explored as a product of hydrogen bond restricted "wobble-in-a-cone" reorientations and that due to the discrete jumps of hydrogen bond reorganization. Additionally, the timescales of hydrogen bond switching and proton transport are presented for bulk water and the H(+) form of hydrated Nafion. The short time scale of proton hopping is found to be independent of Nafion water loading, suggesting the short time dynamics of proton hopping are relatively insensitive to the level of hydration. Furthermore, the long time decay for the forward rate of hydrogen bond switching is shown to be identical to the long time decay in the forward rate of proton hopping, for bulk water and all water loadings of Nafion investigated, suggesting a unified process.
从大量水以及水合Nafion的Na(+)和H(+)形式的分子动力学模拟中计算取向各向异性，然后将其与相应的实验值进行比较。将Laage和Hynes的扩展跳跃模型应用于每个系统的水重排，并将各向异性作为氢键受限的“圆锥内摆动”重排以及氢键重组的离散跳跃所导致的各向异性的乘积进行探讨。此外，还给出了大量水和水合Nafion的H(+)形式的氢键切换和质子传输的时间尺度。发现质子跳跃的短时间尺度与Nafion的水负载量无关，这表明质子跳跃的短时间动力学对水合水平相对不敏感。此外，对于大量水以及所研究的Nafion的所有水负载量，氢键切换正向速率的长时间衰减与质子跳跃正向速率的长时间衰减相同，这表明存在一个统一的过程。
