SELF-AGGREGATES OF HYDROPHOBIZED POLYSACCHARIDES IN WATER - FORMATION AND CHARACTERISTICS OF NANOPARTICLES

Solution properties in water of hydrophobized pullulan containing 1.6 cholesterol groups per 100 glucose units (CHP-55-1.6) were studied by size exclusion column chromatography (SEC), dynamic (DLS) and static light scattering (SLS) methods, electron microscopy, H-1 NMR, and fluorescence spectroscopy. SEC measurements show that CHP (1.0 mg/mL, 0.10 wt%) intermolecularly aggregates and provides relatively monodispersive particles upon ultrasonication. Spherical particles with relatively uniform size (the diameter, 25 +/- 5 nm) were observed in the negatively stained electron microscopy of the aqueous CHP solution. The hydrodynamic radius of the CHP self-aggregate determined by DLS was approximately 13 nm, and the aggregation number determined by SLS was approximately 13; the weight averaged molecular weight of the self-aggregate was 7.6 x 10(5), the root mean-square radius of gyration (R(G)) was 16.8 nm, and the second virial coefficient (A2) was 2.60 X 10 4 (mol mL)/g2. The critical concentration of the self-aggregate formation determined fluorometrically was 0.01 mg/mL. In addition, they showed no surface activity at all up to the concentration of 0.145 mg/mL. Existence of microdomains which consist of both the rigid core of hydrophobic cholesterol and the relatively hydrophilic polysaccharide shell was suggested on the basis of both the line broadening of the proton signal of the cholesterol moiety of CHP(delta = 0.6-2.4 ppm) in the H-1 NMR spectrum and the incorporation of several hydrophobic fluorescent probes in the CHP self-aggregates. The CHP self-aggregates strongly complexed with hydrophobic and less hydrophilic fluorescent probes similarly to the case of cyclodextrin.