Competitive Ion Complexation to Polyelectrolytes: Determination of the Stepwise Stability Constants. The Ca2+/H+/Polyacrylate System

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2007
Author
Calin, David
Companys Ferran, Encarnació
Galceran i Nogués, Josep
Garcés, Josep Lluís
Mas i Pujadas, Francesc
Rey Castro, Carlos
Salvador, José
Puy Llorens, Jaume
Suggested citation
Calin, David; Companys Ferran, Encarnació; Galceran i Nogués, Josep; Garcés, Josep Lluís; Mas i Pujadas, Francesc; Rey Castro, Carlos; ... Puy Llorens, Jaume. (2007) . Competitive Ion Complexation to Polyelectrolytes: Determination of the Stepwise Stability Constants. The Ca2+/H+/Polyacrylate System. Journal of Physical Chemistry B, 2007, vol. 11, núm. 35, p. 10421-10430. https://doi.org/10.1021/jp0741206.
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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.
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http://hdl.handle.net/10459.1/57346
DOI
https://doi.org/10.1021/jp0741206
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Journal of Physical Chemistry B, 2007, vol. 11, núm. 35, p. 10421-10430
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