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

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Solubility Determination, Hansen Solubility Parameters and Thermodynamic Evaluation of Thymoquinone in (Isopropanol + Water) Compositions molecules Article Solubility Determination, Hansen Solubility Parameters and Thermodynamic Evaluation of Thymoquinone in (Isopropanol + Water) Compositions Mohammed Ghazwani 1 , M. Yasmin Begum 1 , Prawez Alam 2, Mohammed H. Alqarni 2, Hasan S. Yusufoglu 2 and Faiyaz Shakeel 3,* 1 Department of Pharmaceutics, College of Pharmacy, King Khalid University, Abha 61441, Saudi Arabia; [email protected] (M.G.); [email protected] (M.Y.B.) 2 Department of Pharmacognosy, College of Pharmacy, Prince Sattam Bin Abdulaziz University, Al-Kharj 11942, Saudi Arabia; [email protected] (P.A.); [email protected] (M.H.A.); [email protected] (H.S.Y.) 3 Department of Pharmaceutics, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia * Correspondence: [email protected] 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 lh, Jouyban–Acree, and Jouyban– Citation: Ghazwani, M.; Begum, Acree–van’t Hoff models. The maximum and minimum x3 values of TQ are recorded in neat IPA M.Y.; Alam, P.; Alqarni, M.H.; (7.63 × 10−2 at 318.2 K) and neat H O (8.25 × 10−5 at 298.2 K), respectively. The solubility of TQ is Yusufoglu, H.S.; Shakeel, F. Solubility 2 Determination, Hansen Solubility recorded as increasing with the rise in temperature and IPA mass fraction in all (IPA + H2O) mixtures, Parameters and Thermodynamic including pure IPA and pure H2O. The HSP of TQ is similar to that of pure IPA, suggesting the Evaluation of Thymoquinone in great potential of IPA in TQ solubilization. The maximum molecular solute-solvent interactions (Isopropanol + Water) Compositions. are found in TQ-IPA compared to TQ-H2O. A thermodynamic study indicates an endothermic and Molecules 2021, 26, 3195. https:// entropy-driven dissolution of TQ in all (IPA + H2O) mixtures, including pure IPA and pure H2O. doi.org/10.3390/molecules26113195 Keywords: apparent thermodynamics; Hansen solubility parameters; isopropanol; solubility; thymo- Academic Editors: Maciej Przybyłek, quinone Tomasz Jeli´nskiand Piotr Cysewski Received: 21 April 2021 Accepted: 23 May 2021 1. Introduction Published: 26 May 2021 Thymoquinone (TQ, Figure1) is a naturally-derived bioactive compound, which Nigella sativa Publisher’s Note: MDPI stays neutral is isolated mainly from the essential oils of [1,2]. In the literature, a vari- with regard to jurisdictional claims in ety of therapeutic/pharmacological effects of TQ have been reported [3–7]. However, a published maps and institutional affil- high amount of TQ is required to produce its therapeutic efficacy, due to its poor water iations. solubility [7,8]. The solubility data of poorly water-soluble naturally-derived bioactive compounds in cosolvent mixtures have a significant role in various industrial processes, such as purifica- tion, recrystallization, drug discovery, and formulation development [9–13]. The potential of isopropanol (IPA) has been proved in enhancing the solubility of various poorly soluble Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. bioactive compounds, such as ferulic acid, hesperidin, iminodibenzyl, and quinocetone This article is an open access article in the literature [10,14–16]. Various formulation strategies, including nanomedicines and distributed under the terms and advanced drug delivery systems, have been adopted for the solubility/dissolution and conditions of the Creative Commons bioavailability improvement of TQ in the literature [17–22]. The solubility of TQ in neat wa- Attribution (CC BY) license (https:// ter (H2O) and neat isopropanol (IPA) has been documented well in the literature [7,23,24]. creativecommons.org/licenses/by/ However, the solubility data of TQ in various (IPA + H2O) mixtures is not studied and 4.0/). reported in the literature. Molecules 2021, 26, 3195. https://doi.org/10.3390/molecules26113195 https://www.mdpi.com/journal/molecules Molecules 2021, 26, 3195 2 of 15 Figure 1. Chemical structure of thymoquinone (TQ). Therefore, the solubility data of TQ in various (IPA + H2O) mixtures, including pure IPA and pure H2O at 298.2–318.2 K and 0.1 MPa, respectively, are studied and reported in this work. The thermodynamic behavior of TQ in various (IPA + H2O) compositions, including neat IPA and neat H2O, was also evaluated. The solubility parameters for free TQ, neat IPA, neat H2O, and various (IPA + H2O) mixtures free of TQ were also pre- dicted to correlate with experimental solubility data. The activity coefficients of TQ were also determined to evaluate the TQ-IPA or TQ-H2O interactions at the molecular level. The physicochemical data of TQ in various (IPA + H2O) combinations reported in this investigation would be applicable in “purification, recrystallization, drug discovery, prefor- mulation studies, formulation development, and preclinical studies” of TQ at laboratory and industrial scale. 2. Results and Discussion 2.1. TQ Solubility Determination The experimental solubilities of TQ in binary (IPA + H2O) mixtures, including pure IPA and pure H2O at 298.2–318.2 and 0.1 MPa, respectively, are included in Table1. The solubility of TQ in pure IPA and pure H2O are documented well in the literature [7,23,24]. However, there are no reports on solubility values of TQ in binary (IPA + H2O) combi- nations. Some other cosolvents, such as dimethyl sulfoxide, carbitol, and polyethyleen glycol-400, etc., have been studied to solubilize TQ in our previous publication [24]. In this study, only IPA was studied in the solubilization of TQ in H2O. The equilibrium solubility −1 −5 of TQ in neat H2O at 298.2 K was reported as 740.63 µg mL (equivalent to 7.75 × 10 in mole fraction) by Salmani et al. [23]. The mole fraction solubility of TQ in neat H2O at 298.2 K was determined as 8.27 × 10−5 by Ahmad et al. [24]. The mole fraction solubility −3 of TQ in neat H2O at 298.2 K was obtained as 8.25 × 10 in this research (Table1). The equilibrium solubility of TQ in neat IPA at 298.2 K was reported as 165.54 mg mL−1 (equiv- alent to 4.55 × 10−2 in mole fraction) by Kalam et al. [7]. The mole fraction solubility of TQ in neat IPA at 298.2 K was reported as 4.51 × 10−2 by Ahmad et al. [24]. The mole fraction solubility of TQ in neat IPA at 298.2 K was recorded as 4.47 × 10−2 in this work. The mole fraction solubilities of TQ in pure IPA and pure H2O at 298.2–318.2 K have also been reported [24]. The graphical analysis between experimental and literature solubility data of TQ in pure H2O and pure IPA at 298.2–318.2 are presented in Figure2A,B, respectively. Molecules 2021, 26, 3195 3 of 15 Table 1. Experimental solubilities (xe) of thymoquinone (TQ) in mole fraction in various isopropyl a alcohol (IPA) + water (H2O) mixtures at 298.2–318.2 K and 0.1 MPa . xe m T = 298.2 K T = 303.2 K T = 308.2 K T = 313.2 K T = 318.2 K 0.0 8.25 × 10−5 9.35 × 10−5 1.06 × 10−4 1.28 × 10−4 1.48 × 10−4 0.1 1.59 × 10−4 1.80 × 10−4 2.05 × 10−4 2.45 × 10−4 2.81 × 10−4 0.2 2.96 × 10−4 3.35 × 10−4 3.79 × 10−4 4.51 × 10−4 5.23 × 10−4 0.3 5.50 × 10−4 6.27 × 10−4 7.15 × 10−4 8.47 × 10−4 9.91 × 10−4 0.4 1.06 × 10−3 1.18 × 10−3 1.35 × 10−3 1.60 × 10−3 1.83 × 10−3 0.5 1.95 × 10−3 2.24 × 10−3 2.53 × 10−3 2.93 × 10−3 3.42 × 10−3 0.6 3.68 × 10−3 4.20 × 10−3 4.71 × 10−3 5.46 × 10−3 6.34 × 10−3 0.7 6.84 × 10−3 7.84 × 10−3 8.87 × 10−3 1.06 × 10−2 1.24 × 10−2 0.8 1.30 × 10−2 1.52 × 10−2 1.72 × 10−2 1.93 × 10−2 2.22 × 10−2 0.9 2.41 × 10−2 2.80 × 10−2 3.16 × 10−2 3.58 × 10−2 4.15 × 10−2 1.0 4.47 × 10−2 5.17 × 10−2 5.85 × 10−2 6.56 × 10−2 7.63 × 10−2 xidl 6.16 × 10−1 6.96 × 10−1 7.85 × 10−1 8.83 × 10−1 9.92 × 10−1 a The average relative uncertainties ur are ur (T) = 0.012, ur (m) = 0.010, u (p) = 0.003 and ur (xe) = 0.014. 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]. The results depicted in Figure2A,B showed an excellent correlation of experimen- tal solubility data of TQ with its literature solubilities in neat H2O and neat IPA at 298.2–318.2 K [24].
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