Excess enthalpies of ternary aqueous solutions of amides and ureas at 298.15 K

Aq. solns. of amides were studied for their importance as uncharged model mols. of structural units of polypeptide chains and proteins. Urea and its alkyl derivs. are known as denaturing agents against proteins. New exptl. calorimetric data for the ternary aq. solns., each contg. one amide and one urea species, are presented, discussed and compared with literature data. The relevance of the weak interactions occurring between these types of cosolutes in water is discussed from the point of view of the biochem. consequences on the stability of proteins. It is confirmed that both polar and hydrophobic intermol. interactions perturb the native conformation of polypeptides and proteins, as they compete with intramol. interactions. Urea is either ineffective or it enhances the hydrophobic interactions, contrary to what apparently is suggested by the increase of soly. of lighter hydrocarbons in urea-water mixts. [on SciFinder(R)]