Pulse radiolysis study on free radical scavenger edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one)

The reactions between edaravone and various one-electron oxidants such as OH, N3, Br2-, and SO4-, have been studied by pulse radiolysis techniques. The transient species produced by the reaction of edaravone with OH radical shows an absorption band with λmax = 320 nm, while the oxidation by N3, Br2-, SO4- and CCl3OO results in an absorption band with λmax = 345 nm. Different from the previous reports, the main transient species by the reaction of edaravone with OH radical in the absence of O2 is attributed to OH-adducts. At neutral condition (pH 7), the rate constants of edaravone reacting with OH, N3, SO4-, CCl3OO, and eaq- are estimated to be 8.5 × 109, 5.8 × 109, 6 × 108, 5.0 × 108 and 2.4 × 109 dm3 mol−1 s−1, respectively. From the pH dependence on the formation of electron adducts and on the rate constant of edaravone with hydrated electron, the pKa of edaravone is estimated to be 6.9 ± 0.1.