Influence of charge density, sulfate group position and molecular mass on adsorption of chondroitin sulfate onto coral

The adsorption of chondroitin sulfate onto granules of natural coral of specific diameter, between 100 and 500 pm, having high calcium content (>98%) and a homogeneous surface was investigated. Several chondroitin sulfate samples desulfated to various extents, with a sulfate to disaccharide ratio (charge density) of 0.98-0.07 and non-sulfated polysaccharide possessing a chondroitin sulfate backbone structure were tested for their ability to adsorb onto coral. Adsorption of chondroitin sulfate onto coral depends on its charge density, as the removal of sulfate groups totally abolishes this capacity. Various chondroitin sulfates of molecular mass from 26,950 to 1140 were also tested. No appreciable effect depending on the molecular mass was evident. Also, chondroitin sulfate fractions with molecular mass of about 3530 (formed by about 6 disaccharide units) and 1140 (formed by about 2 disaccharide units) retain their full capacity to adsorb onto coral. Furthermore, the position of sulfate groups inside the polysaccharide chains does not influence the ability of chondroitin sulfate to adsorb onto coral. In fact, chondroitin sulfate derivatives almost completely sulfated (>90%) in position 4 of galactosamine and chondroitin almost completely (>90%) sulfated in position 6 show a full adsorbtion onto coral. Thus, large amounts of chondroitin sulfate are adsorbed onto coral, and sulfate groups are of paramount importance in the adsorption process. On the other hand, the capacity of chondroitin sulfate to adsorb onto coral is quite aspecific. In fact, it does not depend on the presence of sulfate groups esterified in a specific position or sulfated sequences arranged in blocks but rather on the presence of sulfate groups, and this ability increases with increasing charge density, as indicated by the values of the Langmuir constant, the adsorption capacity, that decreases with decreasing chondroitin sulfate charge density reaching very low values for the totally desulfated polymer. (C) 2002 Elsevier Science Ltd. All rights reserved.