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Séminaire de Véronique Trappe

Hydrophobic hydration : a matter of the mean energetics of water

Véronique Trappe

University of Fribourg, Department of Physics, CH-1700 Fribourg

Hydrophobic hydration : a matter of the mean energetics of water

We explore the phase-behaviour of aqueous solutions of an amphiphilic polymer, which exhibits a lower critical solution temperature (LCST). At low temperatures this amphiphile, poly-N-isopropyl acrylamide (PNiPAM), dissolves in water, while it precipitates out of solution at higher temperatures. The origin of this behaviour is driven by hydrophobic hydration, water-molecules forming stronger and longer-lived hydrogen bonds around a hydrophobic group than in the bulk.
We find that the addition of small amounts of alcohols alters the thermodynamics of PNiPAM-solutions and that these changes are directly correlated to the mixing enthalpy of the water/alcohol mixture itself. This correlation between solution and solvent thermodynamics indicates that the thermodynamics of aqueous solutions of amphiphilic polymers, such as PNiPAM, is primarily determined by the mean energetics of the solvent and quasi-independent of the contributions of the polymer. Such behavior sheds light on the nature of hydrophobic hydration, with wider applicability to the cold denaturation of proteins.