Voltammetric and spectral characterization of two flavonols for assay-dependent antioxidant capacity.
Polyphenolic compounds usually showed different antioxidant capacities depending on the assay methods used. To determine the possible chemical cause for this assay-dependence, two flavonols, kaempferol and morin, were selected as the model molecules for the comparative investigation between electrochemical and chemical oxidations. The electro-oxidation of the flavonols was studied using cyclic voltammetry and in situ UV-Vis spectroelectrochemical technique with a long-optical-path thin-layer electrolytic cell. The spectral changes recorded in different potentials were compared with those in the chemical oxidation by H(2)O(2) or ABTS(*+) radical in the same thin-layer cell. The 4'-OH group of either sample was first oxidized at lower potentials or induced by H(2)O(2), and in this case kaempferol was somewhat more active than morin. With an additional 2'-OH group, morin underwent the secondary oxidation in moderately higher potentials or by ABTS(*+), showing antioxidant capacity about twice of that of kaempferol. This study clarified that the chemical oxidation of a polyphenolic compound by the oxidants with different reactivities, which corresponded to its electro-oxidation in different anodic peaks, had a difference in number of oxidizable OH-groups, leading to the difference in antioxidant capacity.
He
Jian-Bo
JB
MOE-ERC of Bio-process, Anhui Key Laboratory of Controllable Chemical Reaction and Material Chemical Engineering, Hefei University of Technology, Hefei 230009, PR China. jbhe@hfut.edu.cn
Yuan
Sheng-Jie
SJ
Du
Jia-Qi
JQ
Hu
Xin-Ran
XR
Wang
Yan
Y
D000975:Antioxidants / Q000737:chemistry*; D052160:Benzothiazoles / Q000737:chemistry; D004563:Electrochemistry; D005419:Flavonoids / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry; D044949:Kaempferols / Q000737:chemistry*; D010084:Oxidation-Reduction; D013053:Spectrophotometry; D013451:Sulfonic Acids / Q000737:chemistry; D047309:Flavones
D000975:Antioxidants; D052160:Benzothiazoles; D005419:Flavonoids; D006861:Hydrogen Peroxide; D044949:Kaempferols; D013451:Sulfonic Acids; C002502:2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid; C006552:kaempferol; C008548:morin; D047309:Flavones