Mechanistic pathways and identification of the electrochemically generated oxidation products of flavonoid eriodictyol in the presence of glutathione
Résumé
The metabolic oxidation pathways of dietary flavonoid eriodictyol (Er) are not very well-probed. In the present work, the electrochemical oxidation behavior of Er was studied in aqueous Britton-Robinson (B-R) buffer solution using cyclic voltammetry (CV), chronoamperometry (CA), and bulk-electrolysis (BE). The oxidation products and reaction pathways of Er in the absence and the presence of glutathione (GSH) were proposed and identified in view of the results obtained by ultra-high-performance liquid chromatography coupled with mass spectrometry (UPLC-MS). In the absence of GSH, eriodictyol shows one quasi-reversible oxidation process at E-1/2=0.305V, followed by a totally irreversible anodic peak at a more positive potential (E-p(a)=1.05V vs. Ag/AgCl, 3M KCl). Putatively, the first process corresponds to the oxidation of the catechol moiety on the B ring of Er while the second one is attributed to the oxidation of the resorcinol moiety on the A ring. In the presence of GSH, however, the anodic oxidation of Er was proposed to be an ECEC-type mechanism. The Er molecule first underwent a two-electron oxidation coupled with loss of two-proton to generate the corresponding quinone, which was either reduced to the original Er molecule by GSH, or further interacted with GSH to produce mono- and bi- glutathione conjugates of Er. The proposed mechanism was confirmed by digital simulation of the cyclic voltammograms.