On the binding of copper and lead by water-soluble polysaccharides

Optical, chirooptical and thermodynamic techniques have been used to study the binding between copper (II) ions and carboxyethylscleroglucan, oxidised glucomannan, 6-oxychitin and reacetylated chitosan in dilute aqueous solution. For oxidised glucomannan and reacetylated chitosan, the binding of lead was also studied. The results obtained were consistent with the occurrence of a chelate that was evidenced by the existence of a charge transfer band in the near UV region and supported by other experimental data. The variations on binding of the thermodynamic functions Gibbs free energy, enthalpy and hence entropy were computed. Indications on the site(s) of binding were derived. In the case of oxidised glucomannan, the UV spectrophotometry revealed the presence of two sites of binding, the carboxyl groups of glucuronic and mannuronic acids. Finally, the possibility of avoiding misleading results with appropriate procedures is shown.