Abstract
The first two dissociation constants of genistein, pK1 = 7.30 ± 0.07 and pK2 = 9.93 ± 0.05, were determined spectrophotometrically. Simultaneously the second constant, pK2 = 10.18 ± 0.07, was confirmed potentiometrically, and, additionally, the third dissociation constant, pK3 = 11.68 ± 0.15, was determined. The values of the last two dissociation constants were confirmed with the graphical method of Schwarzenbach. The values of constants obtained are pK2 = 10.36 and pK3 = 11.47, respectively. In order to establish the deprotonation site in the genistein molecule, a number of its physicochemical parameters were calculated. Computations were performed with HyperChem v. 7.0 software. A procedure for geometrical optimization (AM1 method, RHF function, Polak-Ribiere algorithm) of different molecular forms was applied. It was found that deprotonation of the neutral molecule of genistein takes place in the following order: 7-OH, 4′-OH and 5-OH.
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