Volumetric properties of amino acids in aqueous solutions of ammonium based protic ionic liquids

Apparent molar volumes, V2,ϕ of amino acids (glycine and dl-α-alanine) in water and in aqueous solutions of ammonium based protic ionic liquids (PILs), namely, propylammonium formate (PAF) and 3-hydroxypropylammonium formate (3-HPAF) determined from precise density measurements, increase with concentration of amino acids and increase in temperature (288.15–318.15) K. Partial molar volume of transfer, ΔtV2° are both positive and negative in case of PAF, whereas only negative ΔtV2° values have been observed in case of 3-HPAF over the studied concentration range. Thermal expansion coefficients, (∂V2°/∂T)P of amino acids in presence of PILs are higher as compared to that observed in water and further, (∂2V2°/∂T2)P values are found to be negative, which suggest that studied amino acids behave as structure breakers in these solutions. Hydration number, nH for studied amino acids in aqueous PILs solutions follows the order: 3-HPAF > PAF, which suggest a strong dehydration effect of PAF.