Monoi H
Biochim Biophys Acta. 1982 Dec 8;693(1):159-64. doi: 10.1016/0005-2736(82)90482-5.
An electrostatic calculation suggests that when an ion is bound near the mouth of a channel penetrating a low-dielectric membrane, a counter ion may form an ion pair with this ion. The tendency towards ion-pair formation is remarkably enhanced at channel mouths by forces (image forces) arising from the charges induced on the boundaries between different dielectrics. The binding constant for the formation of ion-pairs of monovalent ions is estimated under the assumption that local interactions between the counter ion and the channel wall are negligibly small. It is of the order of 1-10 molal-1 or more for the binding of a Cl- (F-) counter ion to an Na+ (Li+) ion if appropriate conditions are fulfilled. The binding constant depends on the position of the binding site, the dimensions and geometries of the channel and channel mouth, and the state of ion loading of the channel, as well as the ionic species. The present results also indicate that when cation (anion) channels have anionic (cationic) groups as integrant parts of their channel walls, interactions between these charged groups and permeant ions are markedly enhanced by the image forces.
静电计算表明，当一个离子结合在穿透低介电常数膜的通道口附近时，一个反离子可能会与该离子形成离子对。在通道口处，由于不同电介质之间边界上感应电荷产生的力（镜像力），离子对形成的趋势显著增强。在假设反离子与通道壁之间的局部相互作用可忽略不计的情况下，估算了单价离子形成离子对的结合常数。如果满足适当条件，对于一个Cl-（F-）反离子与一个Na+（Li+）离子的结合，其结合常数约为1 - 10摩尔浓度-1或更高。结合常数取决于结合位点的位置、通道及通道口的尺寸和几何形状、通道的离子负载状态以及离子种类。目前的结果还表明，当阳离子（阴离子）通道的通道壁含有阴离子（阳离子）基团作为其组成部分时，这些带电基团与渗透离子之间的相互作用会因镜像力而显著增强。
