POTENTIOMETRIC STUDY OF Pd(II) COMPLEXES OF SOME FLAVONOIDS IN WATER-METHANOL-1,4-DIOXANE-ACETONITRILE (MDM) MIXTURE.

The potentiometric method was used to determine the protonation (dissociation) constants for morin, rutin and chrysin and the composition and formation constants of the Pd(II)-flavonoid complexes in the water/methanol/acetonitrile/1,4-dioxane mixture (water/MDM). All investigations were carried out at a constant ionic strength of I = 0.2 (KCI) at 298 K. Morin, rutin and chrysin are polyprotic acids (polihydroxy-flavones) practically insoluble in water, but they are soluble in organic solvents. The mixture of water/MDM is interesting because several solvents were mixed together to produce a solvent having a physical and chemical properties different of the pure components. The two (chrysin) and three (morin, rutin) dissociation constants were obtained by the Bjerrum method (graphic approximations) and numeric data analysis by Hyperquad2008 computer program. Obtained results provide evidence to show that investigated flavonoids in water-MDM solutions form with Pd(II) complexes of composition ML and MI.. The values of the stability constants suggest that the complexes of chrysin, rutin and morin with Pd(II) ions are of medium stability. Moreover, obtained result implies that morin forms the strongest complexes with Pd(II), subsequently rutin and chrysin.