Chorny Ilya, Dill Ken A, Jacobson Matthew P
Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143-2240, USA.
J Phys Chem B. 2005 Dec 22;109(50):24056-60. doi: 10.1021/jp055043m.
In water, positive ions attract negative ions. That attraction can be modulated if a hydrophobic surface is present near the two ions in water. Using computer simulations with explicit and implicit water, we study how an ion embedded on a hydrophobic surface interacts with another nearby ion in water. Using hydrophobic surfaces with different curvatures, we find that the contact interaction between a positive and negative ion is strongly affected by the curvature of an adjacent surface, either stabilizing or destabilizing the ion pair. We also find that the solvent-separated ion pair (SSIP) can be made more stable than the contacting ion pair by the presence of a surface. This may account for why bridging waters are often found in protein crystal structures. We also note that implicit solvent models do not account for SSIPs. Finally, we find that there are charge asymmetries: an embedded positive charge attracting a negative ion is different than an embedded negative charge attracting a positive ion. Such asymmetries are also not predicted by implicit solvent models. These results may be useful for improving computational models of solvation in biology and chemistry.
在水中，阳离子会吸引阴离子。如果在水中的这两种离子附近存在疏水表面，这种吸引力就可以被调节。我们使用含有显式和隐式水的计算机模拟，研究嵌入疏水表面的离子如何与水中附近的另一个离子相互作用。通过使用具有不同曲率的疏水表面，我们发现阳离子和阴离子之间的接触相互作用会受到相邻表面曲率的强烈影响，使离子对稳定或不稳定。我们还发现，表面的存在可以使溶剂分隔离子对（SSIP）比接触离子对更稳定。这可能解释了为什么在蛋白质晶体结构中经常发现桥连水。我们还注意到，隐式溶剂模型无法解释SSIP。最后，我们发现存在电荷不对称性：嵌入的正电荷吸引负离子与嵌入的负电荷吸引正离子是不同的。隐式溶剂模型也无法预测这种不对称性。这些结果可能有助于改进生物学和化学中溶剂化的计算模型。
