INTERACTION MODES IN SOL-GEL TRANSITION OF ALGINATE SOLUTIONS BY THE ADDITION OF CUPRIC IONS

The interaction mode between cupric ions and alginate in aqueous solut ions during sol-gel transition has been experimentally examined at dif ferent temperatures. Some clusters were found to pass through a confor mational transformation as the temperature increased, i.e. clusters fo rmed by intramolecular crosslinks turned into intermolecular crosslink ing clusters. This transformation of the interaction mode is not rever sible as the temperature decreases. The interaction mode between cupri c ions and alginate was re-examined by optical absorption techniques, and results suggest that the coordination of cupric ions mainly occurs to carboxyl groups and that the stoichiometric ratio f is proportiona l to the fraction of crosslinks formed. (C) 1997 by John Wiley & Sons, Ltd.