A Stimulus-Responsive Shape-Persistent Micelle Bearing a Calix[4]arene Building Block: Reversible pH-Dependent Transition between Spherical and Cylindrical Forms

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• 作者：Shota Fujii ; Yusuke Sanada ; Tomoki Nishimura ; Isamu Akiba ; Kazuo Sakurai ; Naoto Yagi ; Efstratios Mylonas
• 刊名：Langmuir
• 出版年：2012
• 出版时间：February 14, 2012
• 年：2012
• 卷：28
• 期：6
• 页码：3092-3101
• 全文大小：577K
• 年卷期：v.28,no.6(February 14, 2012)
• ISSN：1520-5827

文摘

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.