Department of Chemistry and Biochemistry, University of Kitakyushu, Hibikino, Kitakyushu 808-0135, Japan.
Langmuir. 2012 Feb 14;28(6):3092-101. doi: 10.1021/la2037668. Epub 2012 Feb 2.
A series of cationic calix[4]arene-based lipids with alkyl chains of varying length were newly synthesized, and the ones with propyl and hexyl tails, denoted by CaL[4]C3 and C6, respectively, were found to form spherical micelles at low pH (protonated state of the amine headgroup). Upon deprotonation with increasing pH, CaL[4]C3 showed a sphere-to-cylinder transition, while CaL[4]C6 changed from sphere, to cylinder, to monolayer vesicle. Synchrotron small-angle X-ray scattering (SAXS) patterns from both spherical and cylindrical CaL[4]C3 micelles exhibited a sharp intensity minimum, indicating shape monodispersity. The monodispersity of the CaL[4]C3 spherical micelles was further confirmed by analytical ultracentrifugation (AUC). SAXS, AUC, and static light scattering agreeingly indicated an aggregation number of 6. In contrast, CaL[4]C6 exhibited polydispersity with an average aggregation number of 12. When the number of carbons of the alkyl chain was increased to 9 (CaL[4]C9), cylinder formed at low pH, while at high pH, no clear morphology could be observed. The present results indicate that a very precise combination of tail length, head volume, and rigidity of the building block is required to produce shape-persistent micelles and that the shape-persistence can be maintained upon a structural transition. An attempt to reconstruct a molecular model for the spherical CaL[4]C3 micelle was made with an ab initio shape determining program.
一系列具有不同链长的阳离子杯[4]芳烃类脂质被新合成，其中带有丙基和己基尾链的分别被标记为 CaL[4]C3 和 C6，在低 pH（胺头基质子化状态）下形成球形胶束。随着 pH 的增加去质子化，CaL[4]C3 表现出从球体到圆柱的转变，而 CaL[4]C6 则从球体、圆柱到单层囊泡转变。来自球形和圆柱形 CaL[4]C3 胶束的同步加速器小角 X 射线散射（SAXS）图谱均显示出尖锐的强度最小值，表明形态单分散性。球形 CaL[4]C3 胶束的单分散性也通过分析超速离心（AUC）进一步证实。SAXS、AUC 和静态光散射一致表明聚集数为 6。相比之下，CaL[4]C6 表现出多分散性，平均聚集数为 12。当烷基链的碳原子数增加到 9 时（CaL[4]C9），在低 pH 下形成圆柱，而在高 pH 下，无法观察到明确的形态。结果表明，需要非常精确地组合尾链长度、头体积和构建块的刚性，才能产生形态稳定的胶束，并且这种形态稳定性可以在结构转变中保持。尝试使用从头确定形状的程序为球形 CaL[4]C3 胶束重建分子模型。
