Hydrophobic effect: Solubility of non-polar substances in water, protein denaturation and micelle formation

The 'hydrophobic effect' of the dissolution process of non-polar substances in water has been analysed under the light of a statistical thermodynamic molecular model. The model, based on the distinction between non-reacting a nd reacting systems explains the changes of the thermodynamic functions wit h temperature in aqueous systems. In the dissolution of non-polar substance s in water, it follows from the model that the enthalpy change can be expre ssed as a linear function of the temperature (Delta H-app=Delta H+n(w)C(p), T-w). Experimental solubility and calorimetric data of a large number of no n-polar substances nicely agree with the expected function. The specific co ntribution of n(w) solvent molecules depends on the size of solute and is r elated to destructuring (n(w)> 0) of water molecules around the solute. The n the study of 'hydrophobic effect' has been extended to the protein denatu ration and micelle formation. Denaturation enthalpy either obtained by van' t Hoff equation or by calorimetric determinations again depends linearly up on denaturation temperature, with denaturation enthalpy, Delta H-den, incre asing with T. A portion of reaction enthalpy is absorbed by a number n(w) o f water molecules (n(w)> 0) relaxed in space around the denatured moieties. In micellization, an opposite process takes place with negative number of restructured water molecules (n(w)< 0) because the hydrophobic moieties of the molecules joined by hydrophobic affinity occupy a smaller cavity.