PARTIAL MOLAL VOLUME OF SEVERAL ALCOHOLS, AMINO ACIDS, CARBOXYLIC ACIDS, AND SALTS IN 6 M UREA AT 25 DEGREES

Density data have been obtained for homologous series of alcohols, amino acids, and carboxylic acids and their sodium salts at various concentrations in 6 M urea at 25°. Partial molal volumes of the solutes at infinite dilution were found to be larger in urea solutions than in water for all of the compounds studied. The results have been interpreted in terms of a separate contribution of the polar head group and nonpolar side chain. The general increase in ΔV̄t° with increasing length of the hydrocarbon side chain and consideration of solubility parameters are consistent with a structure-breaking role of urea in aqueous solution. Electrostriction of ions appeared to be less in 6 M urea than in water for the compounds studied. Finally, it appears as though differences between the partial molal volume of proteins in water and 6 M urea are to be expected on the basis of the solvent effects observed in this study.