Model studies on the effects of neutral salts on the conformational stability of biological macromolecules. 3. Solubility of fatty acid amides in ionic solutions.
The solubilities of n-hexanamide, n-pentanamide, and n-butyramide in aqueous salt solutions are measured at several temperatures as a function of NaC104 and NaCl con- centrations (these salts representing, respectively, a strongly destabilizing and an essentially "inert" perturbant of macro- molecular stability). NaCl is found to be a more effective salting-out agent than NaC104 for all these amides, and thermodynamic parameters are derived for the transfer of each of these amides (at infinite dilution) from water to 1 M NaC104 or NaCl solutions. The free energy of transfer of a methylene group not directly adjacent to the amide dipole is shown to be a constant for each of these salt systems, corre-