Institute of Polymer Science and Engineering, National Taiwan University, Taipei 106, Taiwan.
J Chem Phys. 2011 Jul 28;135(4):045102. doi: 10.1063/1.3615540.
Simulations based on dissipative particle dynamics are performed to investigate the solubilization mechanism of vesicles by surfactants. Surfactants tend to partition themselves between vesicle and the bulk solution. It is found that only surfactants with suitable hydrophobicity are able to solubilize vesicles by forming small mixed micelles. Surfactants with inadequate hydrophobicity tend to stay in the bulk solution and only a few of them enter into the vesicle. Consequently, the vesicle structure remains intact for all surfactant concentrations studied. On the contrary, surfactants with excessive hydrophobicity are inclined to incorporate with the vesicle and thus the vesicle size continues to grow as the surfactant concentration increases. Instead of forming discrete mixed micelles, lipid and surfactant are associated into large aggregates taking the shapes of cylinders, donuts, bilayers, etc. For addition of surfactant with moderate hydrophobicity, perforated vesicles are observed before the formation of mixed micelles and thus the solubilization mechanism is more intricate than the well-known three-stage hypothesis. As the apparent critical micellar concentration (φ(s,v)(a,CMC)) is attained, pure surfactant micelles form and the vesicle deforms because the distribution of surfactant within the bilayer is no longer uniform. When the surfactant concentration reaches φ(s,v)(p), the vesicle perforates. The extent of perforation grows with increasing surfactant concentration. The solubilization process begins at φ(s,v) (sol), and lipids leave the vesicle and join surfactant micelles to form mixed micelles. Eventually, total collapse of the vesicle is observed. In general, one has φ(s,v)(a,CMC)≤φ(s,v)(p)≤φ(s,v)(sol).
基于耗散粒子动力学的模拟研究了表面活性剂对脂质体的增溶机制。表面活性剂倾向于在脂质体和本体溶液之间分配。研究发现，只有具有适当疏水性的表面活性剂才能通过形成小混合胶束来增溶脂质体。疏水性不足的表面活性剂往往停留在本体溶液中，只有少数进入脂质体。因此，在研究的所有表面活性剂浓度下，脂质体结构保持完整。相反，疏水性过高的表面活性剂倾向于与脂质体结合，因此随着表面活性剂浓度的增加，脂质体的尺寸继续增大。脂质和表面活性剂不是形成离散的混合胶束，而是形成大的聚集体，形状为圆柱、甜甜圈、双层等。对于添加疏水性适中的表面活性剂，在形成混合胶束之前观察到穿孔脂质体，因此增溶机制比著名的三阶段假说更为复杂。当达到表观临界胶束浓度（φ(s,v)(a,CMC）时，形成纯表面活性剂胶束，脂质体变形，因为双层内表面活性剂的分布不再均匀。当表面活性剂浓度达到φ(s,v)(p）时，脂质体穿孔。穿孔程度随表面活性剂浓度的增加而增加。增溶过程始于φ(s,v) (sol），脂质体离开脂质体并与表面活性剂胶束形成混合胶束。最终，观察到脂质体的完全崩溃。一般来说，φ(s,v)(a,CMC）≤φ(s,v)(p）≤φ(s,v)(sol）。
