Hydration Properties of Charge-Modified Phytoglycogen Nanoparticles

Phytoglycogen (PG) nanoparticles are a natural, glucose-based polysaccharide with a dendritic architecture. Their hydration properties are unique, with a high degree of ordering of the sorbed water. We compare the swelling and water ordering in films of native PG with those modified anionically (carboxymethylation; CM-PG) and cationically (glycidyltrimethylammonium chloride; GTAC-PG). We find large differences in both swelling and water ordering between PG and the charge-modified materials, with CM-PG and GTAC-PG having similar swelling but very different degrees of water ordering. We attribute these results to expansion of the particles due to repulsion of the added charges, together with differences in the ability of the substituted functional groups to hydrogen bond with water. We measure very similar hydration properties for native PG and PG subjected to base hydrolysis that mimics exposure to high pH during modification, indicating that the large changes observed for CM-PG and GTAC-PG are determined more by the substituted groups than by structural changes that occur during modification.