Photolytic depolymerization of alginate.

A photochemical reaction has been developed for the partial de-polymerization of sodium alginate, a polysaccharide utilized in medicine, pharmacy, basic sciences and foods. An aqueous solution of sodium alginate was photochemically depolymerized to approximately 40% of its average molecular weight using ultraviolet light in the presence of titanium dioxide catalyst at pH 7 over a period of 3h. The products were separated giving four fractions all having an average molecular weight that was smaller than that of the starting material. Characterization of the guluronate (G) and mannuronate (M) contents, and determination of the M/G ratio of photochemically depolymerized alginate, were accomplished using (1)H NMR spectroscopy. The resulting M/G ratio was compared to that obtained for alginate fractions produced by acid hydrolysis. The M and G content, of each alginate fraction, was also assigned with regards to their occurrence in G-rich, M-rich or M/G heteropolymeric domains. This new depolymerization method might also be applicable in the preparation of alginate oligosaccharides for use in the food and pharmaceutical industries.