Iron complexes of quercetin in aprotic medium. Redox chemistry and interaction with superoxide anion radical

Electrochemical oxidation of quercetin in hydro-alcoholic solution

“…This profile has been attributed to decreased conjugation [13][14][15] and presence of a quinonoid structure as chromophore. 23 Finally, only a single absorption band at 293 nm is observed in the spectrum corresponding to fraction C (the most polar one) ( Figure 9C). Figure 10 shows the structures of quercetin I and its ortho-semiquinone II, ortho-quinone III and para-quinone methides IV, V and VI.…”

Spectroscopic, thermogravimetric and biological studies of Na(I), Ni(II) and Zn(II) complexes of quercetin

“…5) [34]. Although generally the chelating properties of flavonoids have been attributed to the presence of the 3-and 5-hydroxychromone moieties, there were studies revealing the catechol moiety as well [18,26,35]. For example, in the paper of Conrad and Merlin describing the Al(III) complex of quercetin, in the alkaline medium one of the complex form was Al(III)/quercetin 1:1 where the complexing site was catechol group [18].…”

1H NMR and spectroscopic studies of biologically active yttrium (III)-flavonoid complexes

“…Two peaks at 412 (I) and 238 nm(II) in methanol, 375(I) and 262 nm (II) in DMF; at 403(I) and 236(II) in methanol, at 411(I) and 244 nm(II) in DMF are observed in the spectrum of free L1 and L2, respectively [19][20][21][22]. The observed absorption band at higher wavelength (lower frequency) is assigned to the p-p and n-p transitions, and a second band observed at lower wavelength (higher frequency) is due to Main Group Chemistry 135 the p-p and n-s transitions, that correspond to ring A (quinolic system) and ring B (catechol system), respectively [28,29]. The complexes spectra in DMF revealed three bands, I at 457, II at 370 and III at 262 nm; I at 439, II at 360 and III at 285 nm are observed in in Y(L1) 3 and Y(L2) 3 complexes, respectively (Figures 1-3).…”

“…The absorption spectrum of L3, L4 and L5 and their respective complexes in methanol and DMF solvents exhibited only two transitions between 250-700 nm regions. Band I is related to ring A and band II to ring B in these ligands spectrum (Figure 4) [28,29]. After complexation band I was shifted at lower energy (higher wavelength) in comparison to the ligand, and it was suggested that metal is coordinated to ring A in the complexes.…”

“…The spectra of the complexes were different compared with their respective ligands. There are only two absorption bands observed in the spectrum of L1 and L2 in methanol and DMF solutions ( Figures 2 and 3) [16,[27][28][29]. Two peaks at 412 (I) and 238 nm(II) in methanol, 375(I) and 262 nm (II) in DMF; at 403(I) and 236(II) in methanol, at 411(I) and 244 nm(II) in DMF are observed in the spectrum of free L1 and L2, respectively [19][20][21][22].…”