The enthalpically favoured hydration of hydrophobic entities, termed hydrophobic hydration, impacts the phase behaviour of numerous amphiphiles in water. Here, we show experimental evidence that hydrophobic hydration is strongly determined by the mean energetics of the aqueous medium. We investigate the aggregation and collapse of an amphiphilic polymer, poly-N-isopropyl acrylamide (PNiPAM), in aqueous solutions containing small amounts of alcohol and find that the thermodynamic characteristics defining the phase transitions of PNiPAM evolve relative to the solvent composition at which the excess mixing enthalpy of the water/alcohol mixtures becomes minimal. Such correlation between solvent energetics and solution thermodynamics extends to other mixtures containing neutral organic solutes that are considered as kosmotropes to induce a strengthening of the hydrogen bonded water network. This denotes the energetics of water as a key parameter controlling the phase behaviour of PNiPAM and identifies the excess mixing enthalpy of water/kosmotrope mixtures as a gauge of the kosmotropic effect on hydrophobic assemblies.

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Hydrophobic hydration of poly-N-isopropyl acrylamide: a matter of the mean energetic state of water

Preferential solvation parameters of etoricoxib in several aqueous cosolvent mixtures were calculated from solubilities and other thermodynamic properties by using the IKBI method. Cosolvents studied were as follows: 1,4-dioxane, N,N-dimethylacetamide, 1,4-butanediol, N,N-dimethylformamide, ethanol and dimethyl sulfoxide. Etoricoxib exhibits solvation effects, being the preferential solvation parameter δx1,3, negative in water-rich and cosolvent-rich mixtures but positive in mixtures with similar proportions of both solvents. It is conjecturable that the hydrophobic hydration in water-rich mixtures plays a relevant role in drug solvation. In mixtures of similar solvent proportions where etoricoxib is preferentially solvated by the cosolvents, the drug could be acting as Lewis acid with the more basic cosolvents. Finally, in cosolvent-rich mixtures the preferential solvation by water could be due to the more acidic behaviour of water. Nevertheless, the specific solute–solvent interactions in the di...

Preferential solvation of etoricoxib in some aqueous binary cosolvent mixtures at 298.15 K

Values of the Kirkwood–Buff integrals have been obtained from suitable thermodynamic data for 12 binary mixtures of water and organic solvents over the entire composition range where appropriate. The local composition of the environment of each molecule in the mixture is evaluated from these data and is expressed in terms of preferential solvation parameters. These are related to the homo- and hetero-molecular interactions that take place in the mixtures. The systems studied are mixtures of water with hydrogen peroxide, 1,2-ethanediol, 2-propanol, formic, acetic and propanoic acids, formamide, N-methylformamide, N,N-dimethylformamide, N-methylacetamide, hexamethyl phosphoric triamide, sulpholane, propylene carbonate and triethylamine.

D. R. Vollet

Papers

Thermodynamic properties of liquid mixtures. II. Dimethylformamide-water

Thermodynamic properties of liquid mixtures. III. Acetone-water