Potentiometric and Chromatographic Study of Cu(II) and Al(III) Complexes of Quercetin

In this study, the stability constants of the copper(II) and aluminium(III) complexes of quercetin were determined potentiometrically by using Calvin-Bjerrum and Irwing Rossotti methods. The protonation constants of quercetin were found: logK(1) = 11.15 +/- 0.118, logK(2) = 10.42 +/- 0.144, logK(3) = 9.44 +/- 0.162, logK(4) = 8.28 +/- 0.151. For copper complex formation constant was found by Irwing-Rossotti method: logK(1) = 19.92 +/- 0.367 and for aluminium complex complex: logK(1) = 23.02 +/- 0.459. From the results, the components of quercetin / metal complexes are given as 1/1 both copper(II) and aluminium(III). A reversed phase high pressure liquid chromatographic method was developed for the metal complexes which were prepared according to potentiometric results with the ratio quercetin / metal = 1/1. Mobile phase was 0.01 M HClO4/8.33 x 10(-5) M quercetin in Methanol (40/60), column was XTerra RP18, 5 mu m, 4.6 x 150 mm, detector was Diode Array Detector at lambda = 373 ve 421 nm (band width 4nm)