Absolute Hydration Entropies of Alkali Metal Ions from Molecular Dynamics Simulations
Absolute Hydration Entropies of Alkali Metal Ions from Molecular Dynamics Simulations
复制标题
DOI：
10.1021/jp900818z
复制
发表时间：
2009-07-30
影响因子：
3.3
通讯作者：
Aqvist, Johan
中科院分区：
文献类型：
--
作者：
Carlsson, Jens;Aqvist, Johan
结合自由能微扰技术的分子动力学模拟在这项工作中使用的绝对离子水合熵计算。五种碱金属离子的水合熵估计从范特霍夫图使用水合自由能计算在八个不同的温度。考虑到离子-水势仅以绝对水化自由能和离子半径为参数，绝对水化熵与实验数据吻合得很好。需要在每个温度下约3 ns的模拟长度，以实现低于1千卡/摩尔的熵贡献的水合自由能（-T Δ S-hyd）的不确定性。计算熵的不确定性通常比自由能大四倍。使用近似方法来计算水化熵的可能性也进行了研究。在水中产生不带电的货车范德华球的熵与离子的溶剂可及表面积很好地相关。如果不引入与温度相关的经验参数，玻恩连续模型和线性响应近似不能用于预测货车德瓦尔斯球在水中的荷电熵。
Molecular dynamics simulations in combination with the free energy perturbation technique are used in this work to calculate absolute ion hydration entropies. The hydration entropies for five alkali metal ions are estimated from van't Hoff plots using hydration free energies calculated at eight different temperatures. Considering that the ion-water potentials were parametrized only on absolute hydration free energies and ionic radii, the absolute hydration entropies agree very well with experimental data. Simulation lengths of about 3 ns at each temperature were required to achieve an uncertainty below 1 kcal/mol for the entropic contribution to the hydration free energy (-T Delta S-hyd). The uncertainties for the calculated entropies are typically four times larger than for the free energies. The possibility to use approximate approaches to calculate hydration entropies is also investigated. The entropy of creating the uncharged van der Waals spheres in water correlates well with the solvent accessible surface area of the ions. The Born continuum model and the linear response approximation cannot be used to predict the entropy of charging the van der Waals spheres in water without introducing temperature dependent empirical parameters.