Kim J G, Kim J D
Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, Yusong-Gu, Taejon.
J Biochem. 1991 Sep;110(3):436-42. doi: 10.1093/oxfordjournals.jbchem.a123599.
Vesicle to micelle transitions of sonicated liposomes of egg yolk phosphatidylcholine (EPC) induced by a homologous series of nonionic surfactants, poly(oxyethylene) cetyl ethers [POE(n) cetyl ether], were investigated by using the method of turbidity titrations. The turbidities of the mixed dispersions of sonicated vesicles and surfactant were systematically measured as a function of the surfactant added for a wide range of lipid concentrations (from 0.51 to 6.35 mM EPC). From the titration curves, two threshold points representing onset and complete solubilization of liposomal membranes were determined as a probe for the effect of the length of ethylene oxide (EO) moiety on the phase behavior of ternary system of POE(n) cetyl ethers-EPC-excess water. Patterns of turbidity curves and the surfactant concentrations at two threshold points as well as widths of region between two transitions, where lamellar sheets and mixed micelles may coexist, mainly depended on the length of EO head group. With changing the lengths, solubilization of liposomes and phase diagram showed optimal behavior. That is, in the middle range of EO numbers, it resulted in narrowest coexistence region between onset and complete solubilization. Assuming the equilibrium partitioning model, critical effective molar ratios of surfactant to lipid, Rsat, free surfactant concentrations, Dw, and the partition coefficient of surfactant between bilayer and aqueous phase, K, in surfactant-saturated liposomes were quantitatively determined as a function of EO number. Effective ratios, Rsol, and free surfactant concentration in mixed micelles were also determined. In addition, the effects of CMC and HLB of surfactants on the solubilization of liposome were discussed.
采用浊度滴定法研究了一系列同系非离子表面活性剂聚氧乙烯十六烷基醚[POE(n)十六烷基醚]诱导的蛋黄卵磷脂（EPC）超声脂质体向胶束的转变。在较宽的脂质浓度范围（0.51至6.35 mM EPC）内，系统地测量了超声脂质体与表面活性剂混合分散体的浊度随表面活性剂添加量的变化。从滴定曲线中，确定了代表脂质体膜开始溶解和完全溶解的两个阈值点，以此作为环氧乙烷（EO）部分长度对POE(n)十六烷基醚-EPC-过量水三元体系相行为影响的探针。浊度曲线的模式、两个阈值点处的表面活性剂浓度以及两个转变之间层状片层和混合胶束可能共存的区域宽度，主要取决于EO头基的长度。随着长度的变化，脂质体的溶解和相图呈现出最佳行为。也就是说，在EO数的中间范围内，起始溶解和完全溶解之间的共存区域最窄。假设平衡分配模型，定量测定了表面活性剂饱和脂质体中表面活性剂与脂质的临界有效摩尔比Rsat、游离表面活性剂浓度Dw以及表面活性剂在双层和水相之间的分配系数K随EO数的变化。还测定了混合胶束中的有效比率Rsol和游离表面活性剂浓度。此外，还讨论了表面活性剂的临界胶束浓度（CMC）和亲水亲油平衡值（HLB）对脂质体溶解的影响。
