McLaughlin S, Harary H
Biochemistry. 1976 May 4;15(9):1941-8. doi: 10.1021/bi00654a023.
To describe the hydrophobic adsorption of charged molecules to bilayer membranes, one must recognize that the adsorption produces a change in the electrostatic potential at the surface of the membrane. The surface potential produced by the adsorption of the charged molecules can be described most simply by the Gouy equation from the theory of the diffuse double layer. This potential will tend to lower the concentration of the adsorbing ions in the aqueous phase immediately adjacent to the membrane, a phenomenon which can be described by the Boltzmann relation. The number of adsorbed ions is, in turn, a function of the aqueous concentration of these ions at the membrane solution interface and can be described, in the simplest case, by a Langmuir adsorption isotherm. If the ions are regarded as point charges, the combination of the Gouy, Boltzmann, and Langmuir relations may be considered a simplified Stern equation. To test experimentally the applicability of this equation, one should measure both the charge density and surface potential as a function of the concentration of adsorbing molecules in the bulk aqueous phases. Direct, accurate measurements of one of these parameters, the number of moles of 2, 6-toluidinylnaphthalenesulfonate ions bound to vesicles formed from phosphatidylcholine, are available in the literature (Huang, C., and Charlton, J.P. (1972), Biochemistry 11, 735). We estimated the change in the surface potential in two independent ways; by means of conductance measurements with "probe" molecules on planar black lipid membranes and by means of electrophoresis measurements on multilaminar unsonicated vesicles. The two estimates agreed with one another and all of the data could be adequately described by the Stern equation, assuming, at 25 degrees C, a dissociation constant of 2 X 10(-4) M and a maximum number of binding sites of 1/70 A2.
为了描述带电分子在双层膜上的疏水吸附，必须认识到这种吸附会导致膜表面静电势的变化。带电分子吸附产生的表面电势可以用扩散双层理论中的古伊方程最简单地描述。该电势会降低紧邻膜的水相中吸附离子的浓度，这一现象可用玻尔兹曼关系式来描述。吸附离子的数量反过来又是这些离子在膜 - 溶液界面处水相浓度的函数，在最简单的情况下，可以用朗缪尔吸附等温线来描述。如果将离子视为点电荷，那么古伊、玻尔兹曼和朗缪尔关系式的结合可被视为简化的斯特恩方程。为了通过实验检验该方程的适用性，应该测量电荷密度和表面电势作为本体水相中吸附分子浓度的函数。文献中可以找到对其中一个参数的直接、准确测量值，即与由磷脂酰胆碱形成的囊泡结合的2,6 - 甲苯胺基萘磺酸盐离子的摩尔数（黄，C.，和查尔顿，J.P.（1972年），《生物化学》11，735）。我们用两种独立的方法估算表面电势的变化；通过在平面黑色脂质膜上用“探针”分子进行电导测量，以及通过对多层未超声处理的囊泡进行电泳测量。这两种估算结果相互吻合，并且所有数据都可以用斯特恩方程充分描述，假设在25℃时，解离常数为2×10⁻⁴ M，最大结合位点数为1/70 Ų。
