Abstract: In the current work, low molecular mass dextran (with a molecular mass of 5 400 Da) was oxidized by NaClO-NaBr in a basic environment. The content of carboxyl groups gradually increased from 0.05% to 0.8% with increasing oxidant dosage. HPLC analysis indicated that dextran was degraded during the course of oxidation. Moreover, the degree of oxidation gradually increased with the increase of NaClO dosage, whereas the oxidized products were partly degraded into oligosaccharides when the dosage of NaClO was excessive. During the oxidation process the crystalline structures were gradually transformed into amorphous states. Structural characterization by 13C nuclear magnetic resonance (NMR) demonstrated that NaClO-NaBr oxidized the hemiacetal hydroxyl groups at the C1 position and other C positions of the glucose ring into carboxyl groups. This modification improved dextran solubility and the oxidized dextran exhibited good thermal stability. The oxidation of the hydroxyl groups of dextran into carboxyl groups under basic condition and the resulting changes in the physicochemical and structural properties of dextran provide a foundation for the oxidative modification of polysaccharides.

Key words: dextran, polysaccharides, oxidation, physicochemical properties