Explication of molecular interactions between leucine and pharmaceutical active ionic liquid in an aqueous system: Volumetric and acoustic studies

Ionic liquids and their performance for industrial objectives have focused on some of the most academic and scientific research efforts in the last decade. The densities and sound velocities of amino acid (L-leucine) in an aqueous solution of a pharmaceutically active ionic liquid 1-Butyl-3-methylimidazolium hexafluorophosphate [BMIm][PF₆] were measured at different temperatures (293.15 K to 318.15 K) under atmospheric pressure. The experimental results were further used to compute apparent and partial molar volumes, partial molar expansion, Hepler's constant, apparent and partial molar isentropic compression, alongwith corresponding empirical constants (S_v and S_k), intermolecular free length L_f and acoustic impedance Z. The negative values are obtained for partial molar volume of transfer, Δ_tV_Φ^o at all temperatures, and become more negative by increasing the concentration of ionic liquid which indicates predominance of strong electrostriction. The obtained values of these parameters show the structure-making/breaking ability of leucine in solutions of ionic liquid that favours solute–solvent interactions.