Formation of semiquinone radical anion and free radical scavenging reactions of plumbagin: a pulse radiolysis study

Kinetics and mechanism of scavenging of reducing free radicals by plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone) are studied using pulse radiolysis technique. It scavenged superoxide radical, hydroxyethyl radical and hydrated electron with bimolecular rate constants of 8.9 x 10(7), 2.3 x 10(9) and 1.6 x 10(10) M-1 s(-1), respectively in aqueous-alcohol medium. Plumbagin also scavenged linoleic acid peroxyl radical and tyrosyl radical with bimolecular rate constants of 1.0 x 10(8) and 7.0 x 10(6) M-1 s(-1), respectively. Further, redox properties of plumbagin and its transients are studied using standard redox couples and cyclic voltammetry.