Interaction of quercetin with copper ions: complexation, oxidation and reactivity towards radicals
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Quercetin, one of the most common dietary flavonols, was investigated in the presence of Cu(II) ions in methanolic solution in order to obtain some explanation on the mechanism interaction and its action against free radical-mediated damage. The spectroscopic studies (UV–VIS, IR, ESI–MS) were used to assess the extent to which it undergo complex formation through chelation or modification through oxidation. The reaction of quercetin with Cu(II) resulted in the formation of 1:1 metal–ligand complex (λmax = 436 nm) through the carbonyl oxygen and 3-OH group in C ring. Then quercetin is oxidized to the benzoquinone type products. The addition of EDTA destroyed the complex but did not regenerate the whole original spectrum of quercetin. From the other hand, the presence of EDTA inhibits formation of copper–quercetin complex and quercetin oxidation. The antioxidant activity of the Q + Cu solutions was evaluated by using 2,2-diphenyl-1-picrylhydrazyl radical (DPPH∙) radical scavenging method and from an electrochemical point of view. The complex is much more effective as free radical scaveninger than the free flavonoid.
KeywordsFlavonoid Quercetin Copper complexation Antioxidant properties
The authors would like to thank the Structural Research Laboratory at the Department of Chemistry, University of Warsaw for using HPLC–MS. SRL has been established with financial support from European Regional Development Found in the Sectorial Operational Programme “Improvement of the competitiveness of Enterprises” project No. WPK-1/1.4.3./1/2004/72/72/165/2005/U.
- Bukhari SB, Memon S, Mahroof-Tahir M, Bhanger MI (2008) Synthesis, characterization and antioxidant activity copper–quercetin complex. Spectrochim Acta Part A 892:39–46Google Scholar
- Guo M, Perez C, Wei Y, Rapoza E, Su G, Bou-Abdallah F, Chasteen ND (2007) Iron-binding properties of plant phenolics and cranberry’s bio-effects. Dalton Trans 4951–4961Google Scholar
- Jungbluth G, Rühling I, Terns W (2000) Oxidation of flavonols with Cu(II), Fe(II) and Fe(III) in aqueous media. J Chem Soc Perkin Trans 2:1946–1949Google Scholar