Densities of glycine-, L-alanine- and L-valine-xylitol-water ternary solutions have been measured at 298.15 K by an oscillating-tube densimeter. Apparent molar volumes, limiting partial molar volumes, transfer partial molar volumes and hydration numbers for these three amino acids have been calculated. The transfer volumes and hydration numbers have been discussed in terms of a structural hydration interaction model, showing that the dominant interaction between OH group of xylitol and the zwitterionic group of amino acids gave a positive contribution to the transfer volumes. The transfer volumes of amino acids from water to xylitol-water mixed solvents are positive, and increase with increasing xylitol concentration; values of glycine are larger than those of L-alanine and L-valine over the whole range of composition of the mixed solvents studied; the hydration numbers decrease with increasing xylitol concentration.

Key words: amino acid, aqueous xylitol solution, limiting partial molar volume, interaction of structure