Magnetic resonance characterization of betaine micelles and betaine-perfluoropolyether mixed vesicles

Direct (dynamic and static light scattering, LS, and nuclear magnetic resonance, NMR) and indirect (electron spin resonance, ESR) techniques allowed us to obtain details on the dynamics and on the structure of betaine micelles and on mixed betaine-perfluoropolyether (PFPE) vesicles. The mixed vesicles formed in a very restricted range of total surfactant concentration and of betaine mole fraction. The occurrence of unilamellar, monodisperse vesicles has been previously shown by LS measurements (Ristori, S.; Appell, J.; Forte, G. Langmuir 1996, 12, 686). ESR from hydrogenated probes (n-doxylstearic acids, n-DXSA) suggested that separate domains existed in the vesicles, and these radicals localized in the betaine-rich domain. A perfluorinated nitroxide radical was synthesized to study the PFPE domain. From the ESR line shapes the dynamic features of the supramolecular assemblies were obtained. Static LS and QELS (quasi-elastic light scattering) ruled out that the addition of nitroxides in the systems under study had a significant effect on their size and shape. The structural features of the vesicles were also studied by 200-MHz H-1-NMR experiments. On the basis of the structural and dynamic data obtained, a model is presented for the structure of unilamellar betaine/PFPE mixed vesicles. These systems can be used as stable carriers for drugs and biological molecules.