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Título:
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Competitive Ion Complexation to Polyelectrolytes: Determination of the Stepwise Stability Constants. The Ca2+/H+/Polyacrylate System
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Autor/a:
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Calin, David; Companys Ferran, Encarnació; Galceran i Nogués, Josep; Garcés, Josep Lluís; Mas i Pujadas, Francesc; Rey Castro, Carlos; Salvador, José; Puy Llorens, Jaume
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Notas:
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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.
The authors gratefully acknowledge support of this research by the Spanish Ministry of Education and Science (projects CTQ2006-14385 and CTM2006-13583) and by the “Comissionat d’Universitats i Recerca de la Generalitat de Catalunya”. |
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Derechos:
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(c) American Chemical Society, 2007
info:eu-repo/semantics/restrictedAccess |
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Tipo de documento:
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article
publishedVersion |
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Editor:
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American Chemical Society
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