title: 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 3',4'-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.
authors.affiliation: International Antioxidant Research Centre, UMDS-Guy's Hospital, St Thomas's Street, London SE1 9RT, U.K.
authors.forename: J E
authors.initials: JE
authors.lastname: Brown
authors.forename: H
authors.initials: H
authors.lastname: Khodr
authors.forename: R C
authors.initials: RC
authors.lastname: Hider
authors.forename: C A
authors.initials: CA
authors.lastname: Rice-Evans
mesh_terms: D000975:Antioxidants; D003300:Copper / Q000737:chemistry* / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D005419:Flavonoids / Q000737:chemistry* / Q000494:pharmacology*; D006801:Humans; D044949:Kaempferols; D007700:Kinetics; D008077:Lipoproteins, LDL / Q000097:blood* / Q000187:drug effects / Q000378:metabolism; D047311:Luteolin; D015394:Molecular Structure; D011794:Quercetin / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology; D012431:Rutin / Q000737:chemistry / Q000494:pharmacology; D013053:Spectrophotometry; D013329:Structure-Activity Relationship
chemical_list: D000975:Antioxidants; D005419:Flavonoids; D044949:Kaempferols; D008077:Lipoproteins, LDL; C099252:oxidized low density lipoprotein; D012431:Rutin; C006552:kaempferol; D003300:Copper; D004492:Edetic Acid; D011794:Quercetin; D047311:Luteolin