Hydrophobic hydration displayed by the molal shift in the isentropic compressibility

Literature data for the isentropic compressibility and principal dielectric relaxation time of aqueous solutions of hydrophobic solutes are evaluated to investigate the relative molal shifts Bκ and Bd, respectively, of these parameters. In general, Bκ and Bd are correlated: with increasing number of hydrophobic groups per solute, the compressibility decreases and the dielectric relaxation time increases. Effects in the former parameter are smaller than in the latter. Solute isomerisation induces more intricate hydration behaviour. Comparison is also made with results from more complex hydration models, involving both the amount of hydration water and the changes in its relevant parameters.