Center of Biophysical Modeling and Simulation and Department of Chemistry, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, Utah 84112-0850, USA.
J Phys Chem B. 2010 Jan 14;114(1):592-603. doi: 10.1021/jp908768c.
The behavior of the hydrated excess proton near different lipid membranes is studied with the third generation of the multistate empirical valence bond (MS-EVB3) model [Wu, Y. J.; Chen, H. N.; Wang, F.; Paesani, F.; Voth, G. A. J. Phys. Chem. B 2008, 112, 467]. Dioleoylphosphatidylcholine (DOPC), dioleoylphosphatidylethanolamine (DOPE), and dioleoylphosphatidylglycerol (DOPG) are selected as example lipids. In spite of the differences of the head groups, the molecular dynamics simulations show that all the lipid membranes have a proton-collecting antenna effect with no free energy barrier between the bulk water and interface regions. By comparison with classical hydronium model simulations, it is found that an appropriate description of proton Grotthuss shuttling and associated charge defect delocalization are necessary to obtain the correct free energy profile for the hydrated excess proton. In addition, nanosecond time scale sampling is essential to evaluate the free energy profiles, because certain slow motions are needed to stabilize the excess proton in the deep membrane interface region. It is also found that the lateral diffusion coefficients are 1 order of magnitude smaller in the interface region than in bulk water for all the lipids. These coefficients are almost the same as those of the lipid head groups. Finally, since the lipid phosphates may possibly be protonated due to the proton antenna effect of the membrane, phosphate group protonation is investigated and discussed within the MS-EVB framework.
用第三代多态经验价键（MS-EVB3）模型[Wu, Y. J.; Chen, H. N.; Wang, F.; Paesani, F.; Voth, G. A. J. Phys. Chem. B 2008, 112, 467]研究了水合过量质子在不同脂质膜附近的行为。选择二油酰基磷脂酰胆碱（DOPC）、二油酰基磷脂酰乙醇胺（DOPE）和二油酰基磷脂酰甘油（DOPG）作为示例脂质。尽管头基不同，但分子动力学模拟表明，所有脂质膜都具有质子收集天线效应，在体相水和界面区域之间没有自由能屏障。与经典的水合氢离子模型模拟相比，发现质子 Grotthuss 穿梭和相关电荷缺陷离域的适当描述对于获得水合过量质子的正确自由能曲线是必要的。此外，纳秒时间尺度的采样对于评估自由能曲线至关重要，因为某些缓慢的运动对于稳定在深膜界面区域的过量质子是必需的。还发现，对于所有脂质，界面区域的横向扩散系数比体相水小 1 个数量级。这些系数几乎与脂质头基的扩散系数相同。最后，由于膜的质子天线效应，脂质磷酸盐可能发生质子化，因此在 MS-EVB 框架内研究并讨论了磷酸基团的质子化。
