Bolaamphiphilic properties and pH-dependent micellization of quercetin polyglycoside

Effects of Glycon and Temperature on Self-Assembly Behaviors of α-Galactosyl Ceramide in Water

α-Galactosyl ceramide (GalCer) is an anticancer glycolipid consisting of d-galactose and phytosphingosine-based ceramide. Although the amphiphilic structure of GalCer is expected to form self-associates in water, the self-assembly behaviors of GalCer and its derivatives have not been systematically investigated at this moment in spite of its great importance. The evaluation of morphologies and properties of the associates should open new insights into glycolipid chemistry such as the application of GalCer derivatives to a nanocarrier and the elucidation of the detailed pharmacological mechanism of GalCer. Herein, we show the synthesis of the aglycon fragment (Aglycon) of GalCer and the self-assembly behaviors of both GalCer and Aglycon in water. The critical aggregation concentrations of Aglycon and GalCer were determined using UV-vis spectral measurements at various concentrations. The transmission electron microscopy observations of the aqueous sample solutions indicated that the solution of GalCer includes vesicles, while that of Aglycon comprises giant micelles in the absence of vesicles. The vesicle formation in the solution of GalCer was also confirmed by Triton X-100-triggered dye-release experiments. To reveal the effects of glycon on the self-assembly behaviors in detail, we performed the measurements of dynamic light scattering, temperature-dependence of turbidity, differential scanning calorimetry, and wide-angle X-ray diffraction. The results clarify that the glycon moiety of GalCer has a significant role in the formation inhibition of second associates and the plasticization of the hydrophobe. This work will shed light on the other natural glycosides to evaluate the self-assembly behaviors for supramolecular and pharmacological applications in the near future.

Thermoresponsive Structure and Dye Encapsulation of Micelles Comprising Bolaamphiphilic Quercetin Polyglycoside

A bolaamphiphile is a special member of amphiphilic molecules, which contains a hydrophobic skeleton and two water-soluble groups on both ends. Bolaamphiphiles form thermally stable associates in water under lower concentration than those of typical monoheaded amphiphiles, indicating the potential usefulness of bolaamphiphiles as the component of nanomaterials. However, the structural diversity of bolaamphiphiles is limited at this moment. We recently developed the synthesis of quercetin-3-O-polyglycoside (QP) as a new entry of bolaamphiphiles via a one-pot polymerization using sugar-based cyclic sulfite initiated by quercetin skeleton. Herein, we show the bolaamphiphilic properties of QP in detail. The micellization behaviors of QP are systematically investigated through comparison with those of quercetin (Que) and isoquercitrin (IQ) to evaluate the roles of glycone on the micellization of quercetin derivatives. The morphology of the micelles bearing QP is observed by cryo-transmission electron microscopy (cryo-TEM), suggesting the formation of bolaamphiphile-specific giant ribbon-like micelles in addition to spherical micelles. The thermoresponsive micellization behaviors are also discussed through the critical micelle concentration (CMC) values, the dynamic light scattering analyses at various temperatures, and thermal hysteresis of the micellizations. It is indicated that the polysaccharide chains integrated on the surface of micelles would serve as a steric protecting group to endow the micelles with kinetic stability. These results will shed light on natural glycoside skeletons to design a new class of micelles for advanced health applications in near future.

Substituent Optimization of (1 → 2)-Glucopyranan for Tough, Strong, and Highly Stretchable Film with Dynamic Interchain Interactions

Polysaccharide is a naturally abundant material, which is regarded as an indispensable scaffold for a structural material. The properties of polysaccharides are dependent not only on the structure of repeating sugar unit but also the glycosidic position between the repeating units. Herein, we report the development of polysaccharide-based self-standing film consisting of naturally occurring (1 → 2)-glucopyranan skeleton. The self-standing film of (1 → 2)-glucopyranan derivative with hexyl carbamate groups Uret-Glcp(1,2) is found to be highly stretchable and tough, which exhibits maximum stress of σ_max = 1.4 MPa, fracture strain of ε ∼ 800%, and the work of extension at fracture W_ext ∼ 4 MJ m^-3. It is indicated that the interchain hydrogen bonds in Uret-Glcp(1,2) film would serve as energy dissipative bonds for strengthening the film, where the application of mechanical stress to Uret-Glcp(1,2) film induces not only the rapture of physical interchain interactions, but also the formation of intrachain hydrogen bonds along the stretching direction. The effects of substituent and glycosidic position of polysaccharide on the properties are discussed in detail.