Alchemical Free Energy and Hamiltonian Replica Exchange Molecular Dynamics to Compute Hydrofluorocarbon Isotherms in Imidazolium-Based Ionic Liquids
Alchemical Free Energy and Hamiltonian Replica Exchange Molecular Dynamics to Compute Hydrofluorocarbon Isotherms in Imidazolium-Based Ionic Liquids
复制标题
炼金术自由能和哈密顿复制品交换分子动力学计算咪唑基离子液体中的氢氟碳等温线
DOI：
10.1021/acs.jctc.3c00206
复制
发表时间：
2023
影响因子：
5.5
通讯作者：
Maginn, Edward J.
中科院分区：
文献类型：
--
作者：
Wang, Ning;DeFever, Ryan S.;Maginn, Edward J.
离子液体（IL）已经显示出用于利用IL溶剂中的不同气体溶解度的应用的前景，例如，气体分离虽然大多数可用的文献提供了亨利定律常数，有效地估计全等温线的能力是重要的工程设计计算。分子模拟可以用来预测离子液体中气体的等温线。然而，粒子插入或删除在电荷密集的IL介质和IL的缓慢的构象动力学提出了两个采样的挑战，这些系统。因此，我们设计了一种方法，使用汉密尔顿副本交换（HREX）的分子动力学（MD）结合炼金术自由能计算两种不同的氢氟碳化合物（HFC）在咪唑基IL二元混合物的完全溶解度等温线。该工作流程明显快于吉布斯系综蒙特卡罗（GEMC）模拟，GEMC模拟无法处理由离子液体的缓慢动力学引起的缓慢构象松弛。热力学积分、自由能扰动和多态班尼特接受比方法等多种自由能估计器提供了一致的结果。总的来说，模拟的亨利定律常数，等温线曲率，溶解度趋势相当好地匹配实验结果。我们关闭计算两种氢氟碳化合物在IL混合物中的完全溶解度等温线，尚未在文献中报道，展示了这种方法的潜力，用于溶解度预测和设置阶段，为未来的计算筛选研究，寻找“最好的”IL分离共沸氢氟碳化合物混合物。
Ionic liquids (ILs) have shown promise for applications that leverage differential gas solubility in an IL solvent, e.g., gas separations. Although most available literature provides Henry’s law constants, the ability to efficiently estimate full isotherms is important for engineering design calculations. Molecular simulation can be used as a tool to predict full isotherms of gas in ILs. However, particle insertions or deletions in a charge-dense IL medium and the sluggish conformational dynamics of ILs present two sampling challenges for these systems. We therefore devised a method that uses Hamiltonian replica exchange (HREX) molecular dynamics (MD) combined with alchemical free energy calculations to compute full solubility isotherms of two different hydrofluorocarbons (HFCs) in imidazolium-based IL binary mixtures. This workflow is significantly faster than the Gibbs ensemble Monte Carlo (GEMC) simulations which fail to deal with the slow conformational relaxation caused by the sluggish dynamics of ILs. Multiple free energy estimators, including thermodynamic integration, free energy perturbation, and multistate Bennett acceptance ratio method, provided consistent results. Overall, the simulated Henry’s law constant, isotherm curvature, and solubility trends match experimental results reasonably well. We close by calculating the full solubility isotherms of two HFCs in IL mixtures that have not been reported in the literature, demonstrating the potential of this method to be used for solubility prediction and setting the stage for future computational screening studies that search for the “best” IL to separate azeotropic HFC mixtures.