Short-lived phenoxyl radicals formed from green-tea polyphenols and highly reactive oxygen species: an investigation by time-resolved EPR spectroscopy

Abstract

Polyphenols are effective antioxidants and their behavior has been studied in depth. However, a structural characterization of the species formed immediately upon hydrogen-atom transfer (HAT), a key reaction of oxidative stress, has not been achieved. The reaction of catechin and green-tea polyphenols with highly reactive O-centered H-abstracting species was studied at the molecular level and in real time by using time-resolved electron paramagnetic resonance (EPR) spectroscopy. This mirrors the reaction of highly reactive oxygen species with polyphenols. The results show that all phenolic OH groups display essentially identical reactivity. Accordingly, there is no site specificity for HAT and initial antioxidative events are demonstrated to be largely ruled by statistical (entropic) factors.

Keywords: EPR spectroscopy; antioxidants; oxidative stress; polyphenols; radicals.