Comparison of flavonoids and isoflavonoids as antioxidants.
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.
Han
Rui-Min
RM
Department of Chemistry, Renmin University of China, Beijing 100872, China.
Tian
Yu-Xi
YX
Liu
Yin
Y
Chen
Chang-Hui
CH
Ai
Xi-Cheng
XC
Zhang
Jian-Ping
JP
Skibsted
Leif H
LH
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
D000975:Antioxidants; D008081:Liposomes; D012996:Solutions; D047310:Apigenin; D019833:Genistein