DIVALENT-CATION INTERACTIONS WITH A CARBOXYLATED DERIVATIVE OF SCLEROGLUCAN

Divalent cation binding was investigated on a semisynthetic carboxylate derivative obtained from the fungal polysaccharide scleroglucan. Polarography, circular dichroism and isothermal microcalorimetry were used to study both the binding ability of Cu(II), Pb(II), and Zn(II) ions and the macromolecular properties of the systems under investigation. A theoretical model, proposed by Schwarz for the cooperative binding, was used to evaluate binding constants and the parameter a related to the degree of cooperativity. All findings are discussed in terms of the differences in the binding ability of the different cations investigated. Pb(II) ions exhibit the higher affinity for oxidised scleroglucan and, in addition to this, its binding process is characterised by a cooperative behavior due to the onset of a disorder-to-order conformational transition of the polysaccharidic backbone. On the other hand, Cu(II) ions are less effective in the binding and unable to induce the conformational transition.