Solubility of flavonoids in organic solvents

The solubility of quercetin, isoquercitrin, rutin, chrysin, naringenin, and hesperetin was quantified in acetonitrile, acetone, and tert-amyl alcohol. The solubility was strongly affected by both the nature of the solvent and the flavonoid structure. The highest solubility was obtained in acetonitrile for hesperetin (85 mmol.L-1) and naringenin (77 mmol.L-1) and in acetone (80 mmol.L-1) for quercetin. The lowest solubility value was obtained with rutin in acetonirile (0.50 mmol.L-1). The thermodynamic properties of flavonoids were also measured (melting point, enthalpy of fusion, and solid heat capacity) and predicted (liquid heat capacity, solid phase activity, and activity coefficient). Glycosylated flavonoids are characterized by a low melting point and a high enthalpy of fusion compared to the aglycon ones. Contrary to the data reported for other compounds, there is no clear correlation between the solubility of flavonoids and their thermodynamic properties. However, the conformational study showed that the flavonoids having a torsion angle OC2C1 ' C6 ' of 40 degrees are characterized by a high solubility.