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Report No.

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

Lin, M.; Katsumura, Yosuke; Hata, Kuniki ; Muroya, Yusa*; Nakagawa, Keiichi*

The reactions between edaravone and various one-electron oxidants such as OH, N$$_{3}$$, Br$$_{2}$$$$^{-}$$, and SO$$_{4}$$$$^{-}$$ radical have been studied by pulse radiolysis techniques. The transient species produced by the reaction of edaravone with OH radical shows an absorption band with $$lambda$$$$_{rm max}$$ = 320 nm, while the oxidation by N$$_{3}$$, Br$$_{2}$$$$^{-}$$, SO$$_{4}$$$$^{-}$$ and CCl$$_{3}$$OO results in an absorption band with $$lambda$$$$_{rm max}$$ = 345 nm. Different from the previous reports, the main transient species by the reaction of edaravone with OH radical in the absence of O$$_{2}$$ is attributed to OH-adducts. At neutral condition (pH 7), the rate constants of edaravone reacting with OH, N$$_{3}$$, SO$$_{4}$$$$^{-}$$, CCl$$_{3}$$OO, and $$rm e_{ag}^{-}$$ are estimated to be 8.5$$times$$10$$^{9}$$, 5.8$$times$$10$$^{9}$$, 6$$times$$10$$^{8}$$, 5.0$$times$$10$$^{8}$$ and 2.4$$times$$10$$^{9}$$ dm$$^{3}$$ 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$$pm$$0.1.



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