Effects of Sugar Chain Length of Quercetin-3-O-Glycosides on Micellization in Aqueous Media

Abstract

A bolaamphiphile contains a hydrophobic skeleton and two water-soluble groups on the both ends. Bolaamphiphile forms thermally stable associates in water under lower concentration than those of typical mono-headed amphiphiles, indicating the potential usefulness of bolaamphiphile as the component of nano-materials. However, the structural diversity of bolaamphiphiles is limited at this moment. Herein, we show the bolaamphiphilic properties of naturally occurring quercetin glycosides. In addition to natural flavonoids, quercetin (Que) and isoquercitrin (IQ), we have prepared quercetin polyglycoside (QP) via one-pot grafting polymerization using sugar-based cyclic sulfite as a monomer, which plays a crucial role to elucidate the effects of sugar chain length on the micellization. The micellization behaviors of QP are systematically investigated through the comparison with those of Que and IQ. The polyphenolic structures of quercetin derivatives exhibit unique pH-dependency of critical micelle concentration (CMC). While Que hardly forms micelles in pH 10.0 aqueous medium, the solutions of IQ and QP form micelles in the same medium, indicating that the sugar chain would endow the micelles with pH-tolerance. The effects of sugar chain length on the micellization behaviors are discussed through the time-course of UV-vis spectra and the profiles of dynamic light scattering (DLS) analyses. The morphology of the micelles bearing QP is observed by transmission electron microscopy (TEM), suggesting the formation of bolaamphiphile-specific helical ribbon-like micelles. It is indicated that the polysaccharide chains integrated on the surface of micelle would serve as a steric protecting group to afford kinetically stable micelles.