Lichtenberg D
Biochim Biophys Acta. 1985 Dec 19;821(3):470-8. doi: 10.1016/0005-2736(85)90052-5.
This communication addresses the state of aggregation of lipid-detergent mixed dispersions. Analysis of recently published data suggest that for any given detergent-lipid mixture the most important factor in determining the type of aggregates (mixed vesicles or mixed micelles) and the size of the aggregate is the detergent to lipid molar ratio in these aggregates, herein denoted the effective ratio, Re. For mixed bilayers this effective ratio has been previously shown to be a function of the lipid and detergent concentrations and of an equilibrium partition coefficient, K, which describes the distribution of the detergent between the bilayers and the aqueous phase. We show that, similar to mixed bilayers, the size of mixed micelles is also a function of the effective ratio, but for these dispersions the distribution of detergent between the mixed micelles and the aqueous medium obeys a much higher partition coefficient. In practical terms, the detergent concentration in the mixed micelles is equal to the difference between the total detergent concentration and the critical micelle concentration (cmc). Thus, the effective ratio is equal to this difference divided by the lipid concentration. Transformation of mixed bilayers to mixed micelles, commonly denoted solubilization, occurs when the surfactant to lipid effective ratio reaches a critical value. Experimental evaluation of this critical ratio can be based on the linear dependence of detergent concentration, required for solubilization, on the lipid concentration. According to the 'equilibrium partition model', the dependence of the 'solubilizing detergent concentration' on the lipid concentration intersects with the lipid axis at -1/K, while the slope of this dependence is the critical effective ratio. On the other hand, assuming that when solubilization occurs the detergent concentration in the aqueous phase is approximately equal to the critical micelle concentration, implies that the above dependence intersects with the detergent axis at the critical micelle concentration, while its slope, again, is equal to the critical effective ratio. Analysis of existing data suggests that within experimental error both these distinctively different approaches are valid, indicating that the critical effective ratio at which solubilization occurs is approximately equal to the product of the critical micelle concentration and the distribution coefficient K. Since the nature of detergent affects K and the critical micelle concentration in opposite directions, the critical ('solubilizing') effective ratio depends upon the nature of detergent less than any of these two factors.
本通讯探讨了脂质 - 去污剂混合分散体的聚集状态。对近期发表数据的分析表明，对于任何给定的去污剂 - 脂质混合物，决定聚集体类型（混合囊泡或混合胶束）和聚集体大小的最重要因素是这些聚集体中的去污剂与脂质摩尔比，在此表示为有效比，Re。对于混合双层，先前已表明该有效比是脂质和去污剂浓度以及平衡分配系数K的函数，K描述了去污剂在双层和水相之间的分布。我们表明，与混合双层类似，混合胶束的大小也是有效比的函数，但对于这些分散体，去污剂在混合胶束和水介质之间的分布遵循更高的分配系数。实际上，混合胶束中的去污剂浓度等于总去污剂浓度与临界胶束浓度（cmc）之差。因此，有效比等于该差值除以脂质浓度。混合双层向混合胶束的转变，通常称为增溶作用，当表面活性剂与脂质的有效比达到临界值时发生。该临界比的实验评估可基于增溶所需的去污剂浓度对脂质浓度的线性依赖性。根据“平衡分配模型”，“增溶去污剂浓度”对脂质浓度的依赖性在 -1/K 处与脂质轴相交，而该依赖性的斜率是临界有效比。另一方面，假设增溶发生时水相中的去污剂浓度近似等于临界胶束浓度，则意味着上述依赖性在临界胶束浓度处与去污剂轴相交，而其斜率同样等于临界有效比。对现有数据的分析表明，在实验误差范围内，这两种截然不同的方法都是有效的，表明发生增溶作用的临界有效比近似等于临界胶束浓度与分配系数K的乘积。由于去污剂的性质对K和临界胶束浓度产生相反的影响，临界（“增溶”）有效比对去污剂性质的依赖性小于这两个因素中的任何一个。
