Volumetric and acoustic investigation of l-leucine and N-acetyl l-leucine in the aqueous solution of 1-hexyl-3-methylimidazolium bromide [HMIm] [br] at different temperatures

Highlights: • Density/ultrasonic velocity of L-leucine/N-acetyl L-leucine in aqueous [C₆MIM] [Br] solutions. • Positive values of apparent molar volume predict dominance of solute + solvent interactions. • Interpretation of structure making and breaking ability of amino acids. • Pair wise interactions predicted by pair interaction coefficient in the mixtures. Present study reports density (ρ) and ultrasonic velocity (c) for l-leucine and N-acetyl l-leucine in (0.00, 0.005, 0.01, 0.03 and 0.05) mol.kg⁻¹ aqueous solutions of 1-hexyl-3-methylimidazolium bromide [HMIm] [Br] at T = (288.15, 298.15, 308.15 and 318.15) K. Experimental data for density and ultrasonic velocity were used to calculate the apparent molar volumes (V_ϕ), the apparent molar volumes at infinite dilution ($V_{\varphi }^0$), partial molar isentropic compression (K_ϕ,s) and partial molar isentropic compression at infinite dilution ($K_{\varphi ,s}^0$). Further pair and triplet interaction coefficients have been calculated from volumetric and acoustic studies. These Thermodynamic parameters are useful to study the solvation behaviour, structure making and different types of interactions present in the ternary solutions of (amino acids + water + [HMIm] [Br]).