Solubility measurement, thermodynamic correlation and molecular dynamic simulation of naphazoline hydrochloride in four binary solvents

Abstract

Laser monitoring technique was used for the determination of solid-liquid equilibrium solubility of naphazoline hydrochloride (NPZ) in four binary solvents (methanol + ethanol, methanol + isopropanol, 2-methoxyethanol + isopropanol and methanol + ethyl acetate) at T = (278.15–323.15) K and pressure p = 0.1 MPa. In all cases, solubility of NPZ raised with the increment of temperature. The results also indicated that the addition of positive solvents (methanol or 2-methoxyethanol) on the solution of binary solvent mixtures led to increasing solubility of NPZ in all studied binary solvents. The solute-solvent interaction and solvent-solvent interaction were investigated using radial distribution function (RDF). The RDF results revealed that the change of solvent composition varied as the solute-solvent interplay and solvent-solvent interaction, thereby causing the difference of NPZ solubility. Additionally, the measured data was successfully correlated with the Margules, NRTL and UNIQUAC model to investigate theoretically the solubility of NPZ. Computational results proved that the lower mean values of average relative deviation (100ARD) and root-mean square deviation (104RMSD) were obtained to be (1.675) and (2.338) for calculating the solubility of NPZ in investigated systems, further implying that the UNIQUAC model reflected the most accurate descriptions. Using the experimental solubility data, the changes of thermodynamic properties as enthalpy (ΔmixH and ΔdisH), entropy (ΔmixS and ΔdisS) and Gibbs free energy (ΔmixG and ΔdisG) of mixing and dissolution processes were calculated to investigate the solvation behavior of NPZ in studied systems. It was concluded from positive values of entropy and negative values of Gibbs energy change that the mixing and dissolution processes of NPZ in all studied mixed solvents were entropy-driven and spontaneous.