Dissociation Constants and Solubilities of Daidzein and Genistein in Different Solvents

The dissociation constants (pKa) of daidzein and genistein were determined at 298.2 K by ultraviolet (UV) spectroscopy method. The pKa1 and pKa2 values of daidzein are 7.51 ± 0.07 and 9.47 ± 0.14 and ones of genistein are 7.25 ± 0.84 and 9.53 ± 0.15, respectively. The solubilities of daidzein and genistein in water, methanol, ethyl ethanoate, propanone, trichloromethane, and hexane have been measured using UV spectrophotometric method from (288.2 to 328.2) K at atmospheric pressure. The solubilities of daidzein and genistein in all solvents increase with an increase in temperature. The solubility of daidzein in the six solvents was in the order propanone > methanol > ethyl ethanoate > hexane > trichloromethane > water, whereas the solubility order of genistein was propanone > ethyl ethanoate > methanol > hexane > trichloromethane > water. In comparing the solubility of genistein with that of daidzein, the 5-hydroxyl group of genistein causes a significantly higher solubility in methanol and ethyl ethanoat...