Abstract: Densities have been determined for ternary aqueous solutions containing glycine, ethylene glycol or glycerol(cosolvent), with mass fractions of the polyols in cosolventwater mixtures ranging from 0 to 0.50. The apparent molar volumes, the limiting partial molar volumes and hydration numbers of glycine zwitterion have been calculated. The transfer volumes from water to polyolwater mixtures have been obtained and discussed in terms of the structural hydration interaction model. The results obtained have been compared with that in ethanolwater mixtures. It is concluded that the magnitude of enhancement effect on volume is somewhat related to the number of OH groups on alcohol molecules. However, the most important factor that influences volumes is the structural shapes of hydration shells of alcohol molecules. The unusual enhancement effect on volume in ethanolwater mixtures is considered to be related to the fact that the microstructure of the mixtures is heterogeneous and discontinuous.

Key words: Glycine, Polyol-water mixtures, Limiting partial molar volumes, 　Structural interactions