Structural dependence of flavonoid interactions with Cu2+ ions: implications for their antioxidant properties

Abstract

The flavonoids constitute a large group of polyphenolic phytochemicals with antioxidant properties in vitro. The interactions of four structurally related flavonoids (quercetin, kaempferol, rutin and luteolin) with Cu2+ ions were investigated in terms of the extent to which they undergo complex formation through chelation or modification through oxidation, as well as in their structural dependence. The ortho 3ʹ,4ʹ-dihydroxy substitution in the B ring is shown to be important for Cu2+-chelate formation, thereby influencing the antioxidant activity. The presence of a 3-hydroxy group in the flavonoid structure enhances the oxidation of quercetin and kaempferol, whereas luteolin and rutin, each lacking the 3-hydroxy group, do not oxidize as readily in the presence of Cu2+ ions. The results also demonstrate that the reactivities of the flavonoids in protecting low-density lipoprotein (LDL) against Cu2+ ion-induced oxidation are dependent on their structural properties in terms of the response of the particular flavonoid to Cu2+ ions, whether chelation or oxidation, their partitioning abilities between the aqueous compartment and the lipophilic environment within the LDL particle, and their hydrogen-donating antioxidant properties.

Complexing capacity profiles of naturally occurring ligands in Tempranillo wines for Cu and Zn

“…As it can be seen, aromatic  electrons from C ring, and both aromatic  electrons and the hydroxyl group from ring A are directly involved, as well as the hydroxyl and carbonyl groups present in the B moiety. It is noteworthy that binding takes place not only through the typically invoked hydroxyl and carbonyl groups [36] but rather through the aromatic rings of the molecules, as also reported by Vestergaard et al [16].…”

MAPK signaling in neurodegeneration: influences of flavonoids and of nitric oxide

“…Of particular importance to neurodegenerative diseases such as Parkinson's disease is the ability of flavonoids to inhibit peroxynitrite-mediated oxidation of dopamine and peroxynitrite-mediated nitration of tyrosine in vitro by a structure-dependent mechanism involving either the oxidation or nitration of the flavonoid ring system [98,150,151]. In addition, their ability to act as antioxidants in vitro is based on metal-chelating capacity [22,138] and on the quenching of singlet oxygen [203]. However, although flavonoids react rapidly with ROS/RNS in chemical systems in vitro, their reactions in vivo will be dependent on the form that is bioavailable to cells and tissues.…”

7-Rhamnosylated Flavonols Modulate Homeostasis of the Plant Hormone Auxin and Affect Plant Development

“…Flavonols are produced from dihydroflavonols via the activity of the flavonol synthase, and thus represent a side branch of the flavonoid biosynthesis pathway. In Arabidopsis, the flavonols kaempferol, quercetin, and isorhamnetin are glycosylated by one or several sugars, mainly Glc, Rha, and rarely Ara, at the C3 and C7 position of the flavonol backbone (25,26) through the function of UDP-dependent glycosyltransferases (UGTs), 4 some of which have been identified (8, 26 -29). The biological relevance of flavonol glycosylation remains controversial.…”