Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

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 greater than methanol greater than ethyl ethanoate greater than hexane greater than trichloromethane greater than water, whereas the solubility order of genistein was propanone greater than ethyl ethanoate greater than methanol greater than hexane greater than trichloromethane greater than 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 ethanoate, a little higher solubility in trichloromethane (exception 328.2 K), an approximately equivalent solubility in water, and a slightly lower solubility in propanone. The measured solubility data were correlated with a modified Apelblat equation, ?h model, and ideal model. From solubility of daidzein and genistein in these six solvents, the dissolution enthalpy, entropy, and change of the free Gibbs energy were evaluated using the van t Hoff equation.