Ionization Equilibria and Conformational Transitions in Polyprotic Molecules and Polyelectrolytes

Article Article scientifique Article Ionization Equilibria and Conformational Transitions in Polyprotic Molecules and Polyelectrolytes eng 2006 author Garces Gonzalez José Luis 589287 author Koper Ger J. M. author Borkovec Michal 134121 10937-10950 10.1021/jp060684i 1520-6106 https://pubs.acs.org/doi/10.1021/jp060684i The coupling between proton binding and conformational degrees of freedom in polyprotic molecules and polyelectrolytes is studied theoretically. Our approach combines the classical rotational isomeric state (RIS) model developed by Flory and the site binding (SB) model used to treat proton binding equilibria. The properties of the resulting SBRIS model, which treats conformational degrees of freedom and proton binding on equal footing, are studied with statistical mechanical techniques. Quantities of interest, such as titration curves, conformational probabilities, or macroscopic binding constants, are expressed as thermal averages and are evaluated by direct enumeration of states or by transfer matrix techniques. We further demonstrate that in the SBRIS model conformational degrees of freedom can be averaged out, leading to the contracted description within the SB model. In most cases, this contraction leads to higher order interactions, which may not be present at the SBRIS level (e.g., triplet interactions). Several examples are discussed to illustrate the concepts developed. The case of succinic acid exemplifies the situation in its simplest form. The model can further rationalize the very different titration behavior of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA). In particular, the characteristic “jump” in the titration curve of PMAA is described quantitatively and is interpreted in terms of a conformational transition. Dewey 540 40 Département de chimie minérale, analytique et appliquée 145 false Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical 110 22 76e051f8-22c4-46b0-a549-4f212dc90d1a Article (Published version) Public Ionization_MB_2006.pdf 233876 application/pdf openAccess Faculté des sciences / Section de chimie et biochimie / Département de chimie minérale, analytique et appliquée

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Ionization Equilibria and Conformational Transitions in Polyprotic Molecules and Polyelectrolytes	Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical			2006	241	726

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Garces Gonzalez, José Luis