Abstract
In the current study, the solubility of a poorly water-soluble bioflavonoid apigenin in twelve different neat solvents including “water, methanol, ethanol, isopropanol (IPA), ethylene glycol (EG), propylene glycol (PG), 1-butanol, 2-butanol, ethyl acetate (EA), dimethyl sulfoxide (DMSO), polyethylene glycol-400 (PEG-400) and Transcutol®” was measured at temperatures “T=298.2K to 318.2K” and pressure “p=0.1MPa”. The experimental solubilities of apigenin were measured by a static equilibrium method using ultra performance liquid chromatography at 336nm. The measured solubilities of apigenin in mole fraction were correlated with “van't Hoff and Apelblat models”. Good correlation was observed with both models with root mean square deviation values of <3.0% in all solvents evaluated. The solid state characterization of apigenin was performed using differential scanning calorimetry and thermal gravimetric analysis. The solubilities of apigenin in mole fraction were obtained highest in PEG-400 (4.27×10−1) followed by DMSO (4.18×10−1), Transcutol (3.83×10−1), PG (1.50×10−2), EG (8.22×10−3), 1-butanol (9.18×10−4), 2-butanol (8.90×10−4), IPA (6.29×10−4), ethanol (4.86×10−4), EA (4.46×10−4), methanol (2.96×10−4) and water (3.08×10−6) at “T=318.2K” and similar trend was recorded at each temperature evaluated. The solute-solvent interaction was described based on the polarity and activity coefficient. Apparent standard thermodynamic parameters of apigenin in twelve different neat solvents were determined using “apparent thermodynamic analysis” and results showed an “endothermic and entropy-driven dissolution” of apigenin in each solvent evaluated. Based on these results, PEG-400, DMSO and Transcutol were selected as the best solvents and water and methanol were selected as the anti-solvents for apigenin.
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•Solubility of apigenin in twelve different neat solvents was determined.•The mole fraction solubilities of apigenin were recorded maximum in PEG-400.•Measured solubilities of apigenin were correlated well with semiempirical models.•The dissolution of apigenin was recorded as endothermic and entropy-driven.