title: Importance of Proton-Coupled Electron Transfer from Natural Phenolic Compounds in Superoxide Scavenging.
abstract: The superoxide O2(·-) scavenging reaction of (+)-catechin (Cat), quercetin (Que), rutin, and α-tocopherol (α-TOH) as natural phenolic compounds is investigated on the basis of electrochemical and ESR spectral measurements with the aid of density functional theory (DFT) calculations. Reversibility of the O2/O2(·-) redox couple is significantly affected by the presence of the phenolic compounds. The catechol moiety of Cat, Que, and rutin plays an essential role in concerted proton-coupled electron transfer (PCET) to HO2(·) derived from O2(·-) to give H2O2 and the corresponding o-benzoquinone radical anions. On the other hand, the presence of α-TOH causes sequential electron and proton transfers to HO2(·) to give H2O2 and the α-tocopheroxyl radical. These electron transfers in the presence of the phenolic compounds are inferred from the ESR spectral measurements. The DFT calculation results suggest that the O2(·-) scavenging reaction of the natural phenolic compounds proceeds efficiently with the one-step concerted PCET or sequential PCET mechanism.
authors.affiliation: Gifu Pharmaceutical University.
authors.forename: Tatsushi
authors.initials: T
authors.lastname: Nakayama
authors.forename: Bunji
authors.initials: B
authors.lastname: Uno
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D055664:Electrochemical Techniques; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005419:Flavonoids / Q000737:chemistry*; D008968:Molecular Conformation; D011522:Protons; D011789:Quantum Theory; D013481:Superoxides / Q000737:chemistry*; D024502:alpha-Tocopherol / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D005419:Flavonoids; D011522:Protons; D013481:Superoxides; D024502:alpha-Tocopherol