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 solutions during sol-gel transition has been experimentally examined at different temperatures. Some clusters were found to pass through a conformational transformation as the temperature increased, i.e. clusters formed by intramolecular crosslinks turned into intermolecular crosslinking clusters. This transformation of the interaction mode is not reversible as the temperature decreases. The interaction mode between cupric 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 proportional to the fraction of crosslinks formed.