The standard molar enthalpies of solution of glycine, L-α-alanine, L-α-valine and L-α-leucine in aqueous solutions of urea
at 298.15 K were determined by calorimetry. The results obtained were used to calculate the heterogeneous enthalpic interaction
coefficients between the zwitterions of the L-α-amino acids and a molecule of urea in water. The values of the resultant enthalpic
interaction coefficients are interpreted in terms of the effects of the hydrophobic alkyl groups on the interactions between
the zwitterions of the L-α-amino acids and a polar molecule of urea in aqueous solutions.