Investigations of solute–solvent interactions in aqueous solutions of amino acids ionic liquids having the common nitrate as anion at different temperatures

Abstract

Amino acids ionic liquids (AAILs) have huge potential applications in the green chemistry, as these are synthesized from the naturally occurring 20 amino acids and having strong hydrogen bonding ability, hydrophobic tuning, biodegradability, low-toxicity. These specialities are useful for the solubilization and stabilization of biomolecules in aqueous solutions and biofluids. We realize that the buffering capacity of such ionic salts in biofluids may cause some–sort of control in biological processes. It is expected that similar to carbonate–bicarbonate equilibria, the interaction of amino acids may be contributing to ionic interactions. In the present work, we report the synthesis of amino acids–based nitrate protic ionic liquids involving an infrequently used cations amino acids such as glycine ([HOOC–CH2–NH3]+) and ւ–alanine ([HOOC–(CH3)CH–NH3]+) with common inorganic planner anion as nitrate ([NO3]−). To understand the ionic and molecular interactions between the new class of solvents so called “bio–ionic liquids” such as glycine nitrate ([HOOC–CH2–NH3]+ [NO3]−) and ւ–alanine nitrate ([HOOC–(CH3)CH–NH3]+ [NO3]−) in aqueous solutions, the density property has been measured in the concentration range of 0.01974–0.52080 mol·kg−1 at different temperatures (288.15–308.15 K in steps of 5 K) and at 0.1 MPa. Further, experimental density data were used to calculate the apparent molar volume (Vϕ) of solute, partial molar volume of solute (V¯2) and partial molar volume of solvent (V¯1) as a function of concentration at 288.15–308.15 K. Using the appropriate thermodynamic equations incorporating the corrections due to Debye–Hückel limiting law, the apparent molar volume of solute at infinite dilution (Vϕ0) at all studied temperatures has been calculated along with the deviation parameters. The isobaric expansivity coefficient (α) and apparent molar expansivity (Eϕ) of solute at finite concentrations as well as limiting apparent molar expansivity (Eϕ0) of solute are also obtained at 293.15, 298.15 and 303.15 K. The results have been discussed to obtain information about the ion–solvent and ion–ion interactions along with influence of hydrophobic group on the volumetric properties.