Solubility Determination, Hansen Solubility Parameters and Thermodynamic Evaluation of Thymoquinone in (Isopropanol + Water) Compositions

Abstract

This article studies the solubility, Hansen solubility parameters (HSPs), and thermodynamic behavior of a naturally-derived bioactive thymoquinone (TQ) in different binary combinations of isopropanol (IPA) and water (H₂O). The mole fraction solubilities (x₃) of TQ in various (IPA + H₂O) compositions are measured at 298.2-318.2 K and 0.1 MPa. The HSPs of TQ, neat IPA, neat H₂O, and binary (IPA + H₂O) compositions free of TQ are also determined. The x₃ data of TQ are regressed by van't Hoff, Apelblat, Yalkowsky-Roseman, Buchowski-Ksiazczak λh, Jouyban-Acree, and Jouyban-Acree-van't Hoff models. The maximum and minimum x₃ values of TQ are recorded in neat IPA (7.63 × 10^-2 at 318.2 K) and neat H₂O (8.25 × 10^-5 at 298.2 K), respectively. The solubility of TQ is recorded as increasing with the rise in temperature and IPA mass fraction in all (IPA + H₂O) mixtures, including pure IPA and pure H₂O. The HSP of TQ is similar to that of pure IPA, suggesting the great potential of IPA in TQ solubilization. The maximum molecular solute-solvent interactions are found in TQ-IPA compared to TQ-H₂O. A thermodynamic study indicates an endothermic and entropy-driven dissolution of TQ in all (IPA + H₂O) mixtures, including pure IPA and pure H₂O.

Keywords: Hansen solubility parameters; apparent thermodynamics; isopropanol; solubility; thymoquinone.

Figure 1

Chemical structure of thymoquinone (TQ).

Figure 2

Graphical comparison of TQ solubility in (A) neat H₂O and (B) neat IPA with literature values at 298.2–318.2 K; the symbol represents the TQ experimental solubility in (A) neat H₂O and (B) neat IPA, and the symbol represents the TQ literature solubility values in (A) neat H₂O and (B) neat IPA taken from reference [24].

Figure 3

Impact of IPA mass fraction (m) on TQ logarithmic solubility at 298.2–318.2 K.

Figure 4

Graphical correlation of TQ solubility with the modified Apelblat model in various (IPA + H₂O) mixtures at 298.2–318.2 K (the modified Apelblat solubility of TQ is indicated by solid lines, and experimental solubility of TQ is shown by the symbols).