Owenson B, MacElroy R D, Pohorille A
NASA-Ames Research Center, Moffett Field, CA 94035, USA.
J Mol Struct. 1988;179:467-84. doi: 10.1016/0166-1280(88)80142-8.
The capture of chloride from water by the tetraprotonated form of the spherical macrotricyclic molecule SC24 was studied using molecular dynamics simulation methods. This model ionophore represents a broad class of molecules which remove ions from water. Two binding sites for the chloride were found, one inside and one outside the ligand. These sites are separated by a potential energy barrier of approximately 20 kcal mol-1. The major contribution to this barrier comes from dehydration of the chloride. The large, unfavorable dehydration effect is compensated for by an increase in electrostatic attraction between the oppositely charged chloride and cryptand, and by energetically favorable rearrangements of water structure. Additional assistance in crossing the barrier and completing the dehydration of the ion is provided by the shift of three positively charged hydrogen atoms of the cryptand towards the chloride. This structural rigidity is partially responsible for its selectivity.
使用分子动力学模拟方法研究了球形大环分子SC24的四质子化形式从水中捕获氯离子的过程。这种模型离子载体代表了一类能从水中去除离子的广泛分子。发现了两个氯离子结合位点，一个在配体内部，一个在配体外部。这些位点被大约20千卡/摩尔的势能垒隔开。这个势垒的主要贡献来自氯离子的脱水。大的、不利的脱水效应通过带相反电荷的氯离子与穴醚之间静电吸引力的增加以及水结构的能量有利重排得到补偿。穴醚的三个带正电荷的氢原子向氯离子的移动为跨越势垒和完成离子脱水提供了额外帮助。这种结构刚性部分地决定了它的选择性。
