Preferential configurations in solution. Calorimetric study of ternary aqueous systems containing a destructuring agent and derivatives of α-amino acids at 298 K

Abstract

Enthalpies of dilution of ternary aqueous solutions containing α-amino acids or their N-acetyl or N-acetylamide derivatives and urea, glycine, N-acetylglycine and N-acetylglycinamide have been determined by flow microcalorimetry at 298.15 K. Pairwise cross-interaction coefficients of the virial expansion of the excess enthalpies were evaluated. The behaviour of these systems seems to be determined by a balance between favourable hydrophilic–hydrophilic and repulsive hydrophilic–hydrophobic interactions. A common behaviour was shown by every studied series of substances, independently of the nature of the destructuring agent. The pairwise cross-interaction coefficients increase with increasing length of the alkyl side chains until a plateau is attained. This seems to be a general rule when homologous series of solutes having hydrophobic domains interact with a structure-breaker solute.