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 × 107, 2.3 × 109 and 1.6 × 1010 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 × 108 and 7.0 × 106 M−1 s−1, respectively. Further, redox properties of plumbagin and its transients are studied using standard redox couples and cyclic voltammetry.