By using a vitrating digital densimeter (DMA602/60), the densities of glycine and alanine in aqueous methanol, ethanol and propanol solutions were measured at 298.15 K, and the apparent molar volumes calculated. According to McMillan-Mayer approach, the volumetric interaction coefficients were evaluated. The results show that the apparent molar volumes of glycine and alanine in aqueous alkan-1-ol solutions increase with increasing the alkan-1-ol concentration, which demonstrates that glycine and alanine can be classified as hydrophilic ‘structure-breaking’ solute. The homoactic interaction coefficients (Vab) and the triplet interaction coefficients (Vabb and Vaab) of glycine and alanine are all positive. The values of the volumetric pair interaction coefficients of amino acids and amides with alkan-1-ols are all negative and the negative values increase with increasing the alkyl chains. It was discussed in terms of a structural hydration model and a solvent separated association pattern.

Key words: amino acid, alcohol, density, apparent molar volume