Sulfation of extracellular polysaccharides of red microalgae: preparation, characterization and properties

Polysaccharides are natural polymers with a variety of proper-ties that may be translated into significant commercial applications. A program of chemical modifications of the extracellular polysaccharides of red microalgae, such as Porphyridium sp. and Rhodella reticulata, has been undertaken by our group in order to tailor new properties and hence to broaden the spectrum of potential applications. These algal biopolymers are anionic in nature due to the presence of uronic acids (about 10%) and sulfate half esters (about 7%). In the current study, the sulfate content of these biopolymers was increased to 35-40% by means of sulfation agents such as pyridine SO3, DMF (.) SO3 and ClSO3H. Reaction conditions were optimized in a model system based on potato starch as the model polysaccharide (type of reagent. temperature and time of reaction). After work-up procedures, the highest sulfate content was obtained by sulfation of the polysaccharide of Porphyridium sp. with a mixture of ClSO3H and pyridine at 70 degreesC for 1 h. The sulfated products were characterized by chemical and rheological analyses, IR spectroscopy, and GPC-HPLC chromatography. Oversulfated polymers (having sulfate contents exceeding 20170 with high molecular weights were found to inhibit mammalian cell growth when used at certain concentrations; for example, over 80% inhibition was obtained when oversulfated polymers at a concentration of 200 [mug/m] were tested on T-cell lymphoma line 24-1. These preliminary results indicate that the modified polysaccharides do indeed exhibit potential therapeutic properties. (C) 2002 Elsevier Science B.V. All rights reserved.