The depolymerization of sodium alginate by oxidative degradation.

Alginate has been extensively used as a carrier for macromolecules and as gene delivery vehicle. Both properties are molecular weight (Mw) dependent. Herein, we investigated factors affecting the oxidative depolymerization of alginate. The depolymerization process occurred mainly in the first 1 h. The Mw of the depolymerized alginate was influenced by the reaction temperature. At temperature 20 and 30°C, Mw of the alginate fragment kept constant and further Mw decrease was observed at 40°C. Along with the increase of hydrogen peroxide concentration, the Mw of the fragments decreased gradually. Influence of alginate initial concentration was marginal. A linear decrease of Mw was observed when the system pH was in the range of 5-7, whereas no further change was found when the system pH decreased from 7 to 8. Fourier transformed infrared spectroscopy spectra revealed that degradation undergoes by the breakage of the glycosidic bonds of polymers. No structural change was observed during the depolymerization process by UV spectroscopy. Cloud point pH increase was found for alginate 30 k. In summary, this method is an effective and convenient approach for preparing low Mw oligosaccharides from sodium alginate and may be potentially useful for the drug delivery system design with alginate.