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

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• 作者：Calin David ; Encarnació ; Companys ; Josep Galceran ; Josep Lluí ; s Garcé ; s ; Francesc Mas ; Carlos Rey-Castro ; José ; Salvador ; Jaume Puy
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：September 6, 2007
• 年：2007
• 卷：111
• 期：35
• 页码：10421 - 10430
• 全文大小：332K
• 年卷期：v.111,no.35(September 6, 2007)
• ISSN：1520-5207

文摘

This work presents a new methodology aimed at obtaining the stepwise stability constants corresponding tothe binding of ions (or other small molecules) to macromolecular ligands having a large number of sites. Forcomplexing agents with a large number of sites, very simple expressions for the stepwise stability constantsarise. Such expressions are model-independent; that is, they allow the determination of the stepwise stabilityconstants without making any previous assumption of the detailed complexation mechanism. The formalismis first presented for a single complexing ion and further extended to competitive systems where the competingions can display, in general, different stoichiometric relationships. These ideas are applied to the analysis ofexperimental titrations corresponding to competitive binding of calcium ions to poly(acrylic acid) for differentpH 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 (bymeans of the Poisson-Boltzmann equation). After this treatment, the specific proton binding energies showedalmost 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 bidentatebinding of Ca to neighboring groups of a linear chain, is almost independent of the calcium and protoncoverage and ionic strength.