Dutta Ankita, Lazaridis Themis
Department of Chemistry and Biochemistry, City College of New York/CUNY, 160 Convent Avenue, New York, New York 10031, United States.
Graduate Program in Biochemistry, The Graduate Center, City University of New York, 365 Fifth Avenue, New York, New York 10016, United States.
J Phys Chem B. 2024 Dec 12;128(49):12161-12170. doi: 10.1021/acs.jpcb.4c05499. Epub 2024 Dec 3.
Hydronium (HO) and hydroxide (OH) ions perform structural diffusion in water via sequential proton transfers ("Grotthuss hopping"). This phenomenon can be accounted for by interspersing stochastic proton transfer events in classical molecular dynamics simulations. The implementation of OH-mediated proton hopping is particularly challenging because classical force fields are known to produce overcoordinated solvation structures around the OH ion. Here, we first explore the ability of two-particle point-charge models to reproduce both the solvation free energy and coordination number in TIP3P water. We find that this is possible only with unphysical changes in the nonbonded parameters which create problems in proton hopping simulations. We then construct a classical OH model with the charge of oxygen distributed among three auxiliary particles. This model favors a lower coordination number by accepting three hydrogen bonds and weakly donating one. The model was implemented in the MOBHY module of the CHARMM program and was fit to reproduce the experimental aqueous diffusion coefficient of OH. This parameterization gave reasonable electrophoretic mobilities and the expected accelerated transport under nanoconfinement.
水合氢离子（H₃O⁺）和氢氧根离子（OH⁻）在水中通过连续的质子转移（“Grotthuss 跳跃”）进行结构扩散。这种现象可以通过在经典分子动力学模拟中穿插随机质子转移事件来解释。OH⁻介导的质子跳跃的实现尤其具有挑战性，因为已知经典力场会在 OH⁻离子周围产生过度配位的溶剂化结构。在这里，我们首先探索双粒子点电荷模型在 TIP3P 水中重现溶剂化自由能和配位数的能力。我们发现，只有通过非键参数的非物理变化才有可能做到这一点，而这会在质子跳跃模拟中产生问题。然后，我们构建了一个经典的 OH⁻模型，其中氧的电荷分布在三个辅助粒子之间。该模型通过接受三个氢键并弱给出一个氢键，倾向于较低的配位数。该模型在 CHARMM 程序的 MOBHY 模块中实现，并进行参数化以重现 OH⁻的实验水扩散系数。这种参数化给出了合理的电泳迁移率以及在纳米限域下预期的加速传输。
