Potentiometric and spectrophotometric determination of the stability constants of quercetin (3,3′,4′,5,7-pentahydroxyflavone) complexes with aluminium(III) and iron(II)

In this study, the stability constants of the complexes of quercetin formed with aluminium(III) and iron(II) were determined potentiometrically by using the Calvin-Bjerrum and Irving Rossotti methods and spectrophotometrically. The evaluated protonation constants of the ligand were found: log K 1=9.63±0.11 and log K2 = 8.32±013, at 25°C. For the aluminium and iron complexes logarithms of the stability constants were found: for Al: log K1=14.05±0.09, log K 2=10.02±0.12, and for Iron: log K1=9.44±0. 11, log K2=3.86±0.08