Monosaccharide-induced growth and higher order transitions in TPGS micelles

Abstract D -alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) is a nonionic surfactant with low critical micelle concentration. It usually forms spherical core-shell micelles in aqueous media. In this work, we show that these spherical micelles transform to ellipsoid and cylindrical structures upon the incorporation of commonly available monosaccharides, Glucose (GLC), mannose (MAN) and galactose (GAL). The aggregates have been characterized by dynamic light scattering (DLS), small angle neutron scattering (SANS) and nuclear magnetic resonance (NMR) spectroscopy. Our analysis is focused to discuss (a) the effect of sugar concentration, and (b) comparative ability of sugars in triggering structural transitions. It is shown that the transitions and micelle growth arose from the sugar-driven dehydration of head group region. With their higher affinity, sugar molecules approached the shell region and triggered expulsion of water molecules. Although the pattern of transition (micelle to ellipsoid to cylinder) remained common for each sugar, it began at lower concentration of GLC and GAL. NMR experiments showed structural reorganizations in TPGS molecule in the presence of sugar. The outcomes of our study can be applied to tune the viscosity of nonionic surfactant-based long-standing pharmaceutical dispersions.