title: Competitive ion complexation to polyelectrolytes: determination of the stepwise stability constants. The Ca2+/H+/polyacrylate system.
abstract: This work presents a new methodology aimed at obtaining the stepwise stability constants corresponding to the binding of ions (or other small molecules) to macromolecular ligands having a large number of sites. For complexing agents with a large number of sites, very simple expressions for the stepwise stability constants arise. Such expressions are model-independent; that is, they allow the determination of the stepwise stability constants without making any previous assumption of the detailed complexation mechanism. The formalism is first presented for a single complexing ion and further extended to competitive systems where the competing ions can display, in general, different stoichiometric relationships. These ideas are applied to the analysis of experimental titrations corresponding to competitive binding of calcium ions to poly(acrylic acid) for different pH values and ionic strengths. Intrinsic stability constants were estimated from the stepwise stability constants (by removing the corresponding statistical factor), and split into specific and electrostatic contributions (by means of the Poisson-Boltzmann equation). After this treatment, the specific proton binding energies showed almost no dependence on the coverage and ionic strength. Likewise, for the range of concentrations studied, the specific component of the intrinsic stability constants of the calcium ions, calculated assuming bidentate binding of Ca to neighboring groups of a linear chain, is almost independent of the calcium and proton coverage and ionic strength.
authors: Departament de Química, Universitat de Lleida (UdL), Av. Rovira Roure 191, E-25198 Lleida, Spain.
authors: Calin
authors: C
authors: David
authors: Encarnació
authors: E
authors: Companys
authors: Josep
authors: J
authors: Galceran
authors: Josep Lluís
authors: JL
authors: Garcés
authors: Francesc
authors: F
authors: Mas
authors: Carlos
authors: C
authors: Rey-Castro
authors: José
authors: J
authors: Salvador
authors: Jaume
authors: J
authors: Puy
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000737:chemistry*; D002413:Cations, Divalent / Q000737:chemistry; D004573:Electrolytes / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D007700:Kinetics; D046911:Macromolecular Substances / Q000737:chemistry; D011522:Protons; D055672:Static Electricity
chemical_list: D000180:Acrylic Resins; D002413:Cations, Divalent; D004573:Electrolytes; D046911:Macromolecular Substances; D011522:Protons; C006903:carbopol 940; D006859:Hydrogen; D002118:Calcium