Dynamics and energetics of hydrophobically confined water
Dynamics and energetics of hydrophobically confined water
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DOI：
10.1103/physreve.85.051506
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发表时间：
2012-05-23
影响因子：
2.4
通讯作者：
Siva, Karthik
中科院分区：
文献类型：
--
作者：
Bauer, Brad A.;Ou, Shuching;Siva, Karthik
限制在自组装实体之间区域的水的影响与许多环境有关，如大分子缔合、蛋白质折叠、蛋白质-配体缔合和纳米材料自组装。因此，评估承压水的影响，以及当前建模技术捕捉承压水显著特征的能力是重要的和及时的。我们给出了分子动力学模拟结果，研究了承压水对平均力势的定性特征，描述了大平面疏水平板自组装的自由能量学。我们考虑了几种常见的显式水模型，包括TIP3P、TIP4P、SPC/E、TIP4P-FQ和SWM4-NDP，后两种模型是可极化模型。对填充和卸载两块板之间受限体积的自由能(都是在受限水分子平均数和占据深度的背景下)的检查表明，TIP4P-FQ水分子通常在间隔距离大于相同条件下观察到的其他模型的受限体积时占据受限体积。TIP4P-FQ水的这种倾向与TIP4P-FQ水中板-板结合平均作用力的势能缺乏明显的势垒之间的联系是通过人工但系统地在低板-板分离距离下用TIP4P-FQ水填充受限体积来探索的。当使用这种方法将TIP4P-FQ的临界分离距离[表示从空置(干)受限内部到填充(湿)内部的交叉]减小0.5埃时，观察到屏障；我们基于在这些低分离时受限水分子引入的增加的阻力来使这种影响合理化。我们还考虑了疏水分子之间受限区域中水分子的动力学。我们发现，TIP4P-FQ水模型表现出非块状动力学，相对于块体具有增强的横向扩散。这与分子间水-水相互作用的减弱是一致的，这表明分子偶极矩在板间区域减小。速度自相关函数和相关功率谱分析表明，TIP4P-FQ在板间距为14.4埃时的板间区域接近纯水汽液界面的特征。这与其他水模型(包括可极化的SWM4-NDP模型)形成了鲜明的对比。
The effects of water confined in regions between self-assembling entities is relevant to numerous contexts such as macromolecular association, protein folding, protein-ligand association, and nanomaterials self-assembly. Thus assessing the impact of confined water, and the ability of current modeling techniques to capture the salient features of confined water is important and timely. We present molecular dynamics simulation results investigating the effect of confined water on qualitative features of potentials of mean force describing the free energetics of self-assembly of large planar hydrophobic plates. We consider several common explicit water models including the TIP3P, TIP4P, SPC/E, TIP4P-FQ, and SWM4-NDP, the latter two being polarizable models. Examination of the free energies for filling and unfilling the volume confined between the two plates (both in the context of average number of confined water molecules and "depth" of occupancy) suggests TIP4P-FQ water molecules generally occupy the confined volume at separation distances larger than observed for other models under the same conditions. The connection between this tendency of TIP4P-FQ water and the lack of a pronounced barrier in the potential of mean force for plate-plate association in TIP4P-FQ water is explored by artificially, but systematically, populating the confined volume with TIP4P-FQ water at low plate-plate separation distances. When the critical separation distance [denoting the crossover from an unoccupied (dry) confined interior to a filled (wet) interior] for TIP4P-FQ is reduced by 0.5 angstrom using this approach, a barrier is observed; we rationalize this effect based on increased resistant forces introduced by confined water molecules at these low separations. We also consider the dynamics of water molecules in the confined region between the hydrophobes. We find that the TIP4P-FQ water model exhibits nonbulklike dynamics, with enhanced lateral diffusion relative to bulk. This is consistent with the reduced intermolecular water-water interaction indicated by a decreased molecular dipole moment in the interplate region. Analysis of velocity autocorrelation functions and associated power spectra indicate that the interplate region for TIP4P-FQ at a plate separation of 14.4 angstrom approaches characteristics of the pure water liquid-vapor interface. This is in stark contrast to the other water models (including the polarizable SWM4-NDP model).