Solubilization, Hansen solubility parameters, and thermodynamic studies of delafloxacin in (transcutol + 1-butyl-3-methyl imidazolium hexafluorophosphate) mixtures

Abstract

The solubilization, Hansen solubility parameters (HSPs), and thermodynamic properties of delafloxacin (DLN) in various unique combination of Transcutol-HP® (THP) and 1-butyl-3-methyl imidazolium hexafluorophosphate ionic liquid (BMIM-PF₆) mixtures were evaluated for the first time in this research. The 'mole fraction solubilities (x₃)' of DLN in different (THP + BMIM-PF₆) compositions were determined at 'T = 298.2-318.2 K' and 'p = 0.1 MPa'. The HSPs of DLN, neat THP, neat BMIM-PF₆, and binary (THP + BMIM-PF₆) compositions free of DLN were also determined. The x₃ data of DLN was regressed using 'van't Hoff, Apelblat, Yalkowsky-Roseman, Jouyban-Acree and Jouyban-Acree-van't Hoff models' with overall error values of less than 3.0%. The highest and lowest x₃ value of DLN was recorded in neat THP (5.48 × 10^-3 at T = 318.2 K) and neat BMIM-PF₆ (6.50 × 10^-4 at T = 298.2 K), respectively. The solubility of DLN was found to be enhanced significantly with an arise in temperature in all (THP + BMIM-PF₆) compositions including pure THP and pure BMIM-PF₆. However, there was slight increase in DLN solubility with increase in THP mass fraction in all (THP + BMIM-PF₆) mixtures. The HSP of pure THP and pure BMIM-PF₆ were found very close to each other, suggesting the great potential of both solvents in DLN solubilization. The maximum solute-solvent interactions at molecular level were recorded in DLN-THP compared to DLN-BMIM-PF₆. An 'apparent thermodynamic analysis' study indicated an 'endothermic and entropy-driven dissolution' of DLN in all (THP + BMIM-PF₆) compositions including neat THP and BMIM-PF₆.

Keywords: Apparent thermodynamics; BMIM-PF6; delafloxacin; ionic liquid; solubility; transcutol.