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Séminaire 07.06.2013 à 14h

par Benjamin Rotenberg - 27 mai 2013

Vojko Vlachy, de l’Université de Ljubljana (Slovénie), présentera un séminaire le 7 juin 2013 à 14h00 dans la bibliothèque du laboratoire PECSA (7e étage, bâtiment F, porte 754) intitulé :

Presence of hydrophobic groups may modify the specific ion effect in aqueous polyelectrolyte solutions


Biologically important macromolecules contain in addition to charges also the non-polar groups. Here we report the studies of aliphatic x, y–ionenes, that is, cationic poly-electrolytes with the repeating unit


where integers x and y denote the number of methylene groups between the adjacent nitrogen atoms. We had synthesized and studied ionenes with x,y values, ranging from 3,3- to quite hydrophobic 12,12-ionenes with various counterions (F, Cl, Br, I, and others) and in mixture with simple salts in water. Various experimental methods, from classical transport and thermodynamic measurements to the dielectric relaxation (DRS) and small angle neutron scattering (SANS), were applied.

The most important findings are : i) enthalpies of dilution and mixing can be, in contrast with the continuum solvent theories, either negative or positive , ii) there is strong correlation of the enthalpy of mixing of low-molecular electrolyte and polyelectrolyte, with the enthalpy of hydration of the counterion species. iii) The salts, when ordered by heat effects produced in mixing of NaF and NaBr with 3,3-, 6,9-, or 6,12-ionene fluorides and bromides, follow the opposite ordering than in the case when the same alkali halide salts when mixed with more hydrophobic 12,12-ionene salts. In other words, the presence of hydrophobic groups may reverse the Hofmeister series. iv) SANS measurements indicated that ``polyelectrolyte’’ peak, present in solutions with F counterions, vanishes in solutions of Br-ionenes. v) Ion binding, calculated from transport properties, depends on the nature of counterion.

In summary, the experiments, including the preliminary study of ionene complexation with oppositely charged surfactants, revealed ion-specific effects, depending on the hydrophobicity of the ionene studied. We used some of these conclusions, in conjecture with the integral equation approach, to model the solubility of Lysozyme in presence of different salts. Most of the talk will be based on the recent papers listed below.

Références :

[1] M. Lukšič, M. Bončina, M. Druchok, and V. Vlachy*, Phys. Chem. Chem. Phys, 14, 2024–2031 (2012).

[2] M. Seručnik, M. Bončina, M. Lukšič, and V. Vlachy*, Phys. Chem. Chem. Phys, 14, 6805–6811 (2012).

[3] N. Malikova*, S. Čebašek, V. Glenisson, G. Carrot, and V. Vlachy, Phys. Chem. Chem. Phys, 14, 12898-12904 (2012).

[4] S. Čebašek, M. Seručnik, and V. Vlachy*, J. Phys. Chem. B, Condens. mater. surf. interfaces biophys., 117, 3682-3688 (2013).

[5] P. Rodič, M. Bratuša, M. Lukšič, B. Hribar–Lee*, V. Vlachy, and B. Hribar Lee, Colloids and Surfaces A : Physicochemical and Engineering Aspects, 424, 18-25 (2013).

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