Apparent molar volumes of glycine, L-alanine and L-serine in aqueous urea at 298.15 K were determined and transfer partial molar volumes from water to aqueous urea were derived. The results, along with transfer enthalpies of amino acids from water to aqueous urea in our previous work, were used to investigate the characteristic of structure of urea-water mixtures and its influence on the interaction between amino acids and urea on the basis of hydration cosephere overlapping model. Regular breaks were found on the urea concentration dependence of transfer partial molar volumes and transfer enthalpies of amino acids, which was attributed to the change of solvent structure due to self-association of urea molecules in aqueous solution and its influence on the structure interaction with amino acids. The results also indicated that more hydrophobic amino acids undergo more dehydration effect due to the structure interaction with urea.

Key words: amino acid, urea, limiting partial molar volume, interaction