Free Radical Scavenging Reactions of Tetrahydroxyquinone: A Pulse Radiolysis Study

Free radical induced redox reaction kinetics and mechanism of tetrahydroxy-1,4-benzoquinone (THQ) has been studied using pulse radiolysis technique. THQ efficiently scavenged hydrated electron, superoxide radical anion, ethanol radical, hydroxyl radical, azidyl radical, thiocyanate radical anion, sulfate radical anion, haloperoxyl radical, lipid peroxyl radical, tryptophanyl radical and tyrosyl radical. Transient absorption spectra of THQ semiquinone radical anion, THQ radical cation and THQ radical produced with these free radicals and rate constants for these reactions have been studied. A probable mechanism of free radical induced redox reactions of THQ has been proposed. Reaction of THQ with free radicals and cyclic voltammetry measurements suggest its oxidation potentials at 0.81 V and 0.94 V vs NHE. To the best of our knowledge, free radical reactions of THQ have been reported for the first time.