title: Comparison of flavonoids and isoflavonoids as antioxidants.
abstract: The isoflavonoid genistein was found to be a better antioxidant than the isomeric flavonoid apigenin in phosphatidyl liposomes at pH 7.4. The higher antioxidation activity of genistein compared with apigenin is in agreement with its lower oxidation potential (0.73 vs 0.86 V as determined by cyclic voltammetry in aqueous solution of pH= 7.4), lower dissociation enthalpy (87.03 vs 87.88 kcal mol(-1) as calculated for the more reducing 4'-hydroxyl group), and higher radical scavenging capacity in the TEAC assay. On the basis of quantum mechanical calculations for genistein and apigenin in comparison with the flavonoid naringenin and the isoflavonoids puerarin, daidzein, and equol, a lower dipole moment and a larger deviation for the A-to-B dihedral angle from coplanarity (39.3 degrees for genistein, 18.5 degrees for apigenin) are suggested to be important for the increased antioxidant efficiency at water/lipid interfaces among (iso) flavonoids with an equal number of phenolic groups.
authors.affiliation: Department of Chemistry, Renmin University of China, Beijing 100872, China.
authors.forename: Rui-Min
authors.initials: RM
authors.lastname: Han
authors.forename: Yu-Xi
authors.initials: YX
authors.lastname: Tian
authors.forename: Yin
authors.initials: Y
authors.lastname: Liu
authors.forename: Chang-Hui
authors.initials: CH
authors.lastname: Chen
authors.forename: Xi-Cheng
authors.initials: XC
authors.lastname: Ai
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Zhang
authors.forename: Leif H
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D047310:Apigenin / Q000737:chemistry*; D055598:Chemical Phenomena; D004563:Electrochemistry; D019833:Genistein / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008081:Liposomes / Q000737:chemistry; D010084:Oxidation-Reduction; D012996:Solutions; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D000975:Antioxidants; D008081:Liposomes; D012996:Solutions; D047310:Apigenin; D019833:Genistein