Stability of Ferric Complexes with 3-Hydroxyflavone (Flavonol), 5,7-Dihydroxyflavone (Chrysin), and 3‘,4‘-Dihydroxyflavone

Abstract

The acid dissociation and ferric stability constants for complexation by the flavonoids 3-hydroxyflavone (flavonol), 5,7-dihydroxyflavone (chrysin), and 3',4'-dihydroxyflavone in 50:50 (v/v) ethanol/water are determined by pH potentiometric and spectrophotometric titrations and the linear least-squares curve-fitting program Hyperquad. Over the entire range of pH and reagent concentrations spanning the titration experiments, the stoichiometry for iron-flavonoid complex formation was 1:1 for all three flavonoids examined. The three flavonoids were chosen for their hydroxy substitution pattern, with each possessing one of the three most commonly suggested sites for metal binding by the flavonoids. On the basis of the calculated stability constants, the intraflavonoid-binding site competition is illustrated as a function of pH via speciation curves. The curves indicate that the binding site comprised of the 3',4'-hydroxy substitutions, the catecholic site, is most influential for ferric complexation at the physiological pH of 7.4. The possibility for antioxidant activity by flavonoid chelation of ferric iron in the presence of other competitive physiological complexing agents is demonstrated through additional speciation calculations.

In vitro analysis of iron chelating activity of flavonoids

“…The 5-hydroxy-4-keto site is another possible iron binding site, but this study showed and other researchers confirmed that its importance is lower when compared to the previously mentioned sites [7]. In addition, the complex formed at this site is less stable and iron can be easily released at more acidic conditions (see Fig.…”

“…deferoxamine (Fig. 1B), is missing [5][6][7][8][9][10][11]. The published studies uniformly reported the three most common iron binding sites of flavonoids: 1) catecholic ring B, 2) 3-hydroxy-4-keto and 3) 5-hydroxy-4-keto conformation [6,8].…”

Acid–base equilibrium of puerarin in CTAB micelles

“…For the second equilibrium ( Fig. 2(b)), around a pH close to pK 2 the peak at 260 nm due to the dianionic forms of puerarin increases and shows a red shift [20]. In the studied range of pH values, it is evident that tow isosbestic points exist at the wavelength point where the spectra cross up (315 nm ( Fig.…”

Electronic Description of Few Selected Flavonoids by Theoretical Study

“…Taxifolin has no conjugation, due to the absence of C2-C3 double bond, hence 3-O has higher charge than 5-O. Some studies report that 3'-4' site is the first chelation site [35]. This may be due to different solvent conditions (acidic or basic).…”