ROLE OF COSOLVENT IN HYDROPHOBIC INTERACTIONS - CALORIMETRIC STUDIES OF ALKANOLS IN CONCENTRATED AQUEOUS-SOLUTIONS OF UREA AT 298 K

Calorimetric measurements have been carried out at 298.15 K on aqueous solutions of 7 mol kg(-1) urea containing alkan-m-ols and alkan-m,n-d iols in order to obtain more information on the influence of urea on t he hydrophobic solvation and interactions. The pairwise interaction co efficients of the virial expansion of the excess enthalpies were found to be positive and generally lower than the corresponding values in w ater. The only exception concerns pentan- and hexan-2- and -3-ols, who se coefficients in the mixed solvent are higher. These coefficients we re rationalized according to the preferential configuration model. Ure a mainly solvates the hydroxy groups. Hydrophobic interactions are att enuated by the presence of such a large amount of urea, thus indicatin g that the hydrophobic cosphere of the alkanols must be reduced with r espect to that in pure water. The interaction mechanism in water and i n concentrated urea solutions does not seem to be alterated. The data show that in 7 mol kg(-1) urea the nature of the hydration cosphere of the alkyl chain does not change, so that water still plays the major role in this interaction process between two hydrated molecules.