Interaction of quercetin with copper ions: complexation, oxidation and reactivity towards radicals

Abstract

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 (λ(max) = 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.

Quercetin Affects Erythropoiesis and Heart Mitochondrial Function in Mice

“…Our previous research [30] exposed that mild copper deprivation in mice is correlated with a decreased protein expression and activity of Complex IV at the level of OXPHOS supercomplexes along with a decrease in the ceruloplasmin levels. Our present results are suggesting a potential interaction between quercetin and copper ions, which is in accordance with in vitro observations made by Pękal et al [71]. Laccases are multicopper oxidases structurally and functionally similar to ceruloplasmin.…”

How plants cope with heavy metals

“…Recent results showed evidence that flavonoids can facilitate heavy metal tolerance in A. thaliana (Keilig and Ludwig-Müller 2009). Besides iron chelation, quercetin undergoes a complexation with copper ions (El Hajji et al 2006Pekal et al 2011) and uranium (Geipel et al 2010). An example to underline this issue: Recently a close relation between iron and uranium uptake was shown in A. halleri , where iron starvation greatly enhanced uranium uptake (Viehweger and Geipel 2010).…”

Inhibitory effect of plant phenolics on fMLP-induced intracellular calcium rise and chemiluminescence of human polymorphonuclear leukocytes and their chemotactic activityin vitro

“…and Fe 2+ ) (Kim et al, 2013;Pekal et al, 2011) one may speculate that quercetin and catechol can bind Ca 2+ and thus diminish the Ca 2+ -dependent signal from Fura 2. Nevertheless, a supposed chelation of extracellular and intracellular Ca 2+ by both these compounds would be negligible considering the 200-fold higher Ca 2+ level to polyphenol concentration in the buffer used for the preparation of experimental cell suspensions.…”