Pulse radiolysis and theoretical study on the radical scavenging capacity of edaravone and its derivatives
Hata, Kuniki ; Katsumura, Yosuke; Lin, M.; Muroya, Yusa*; Fu, H.*; Kudo, Hisaaki*; Nakagawa, Keiichi*; Nakagawa, Hidehiko*
Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) is known as a neuroprotective as well as a radioprotective drug. This is thought to be due to its potent free radical scavenging capacity. To help for a better understanding about the mechanism of oxidation reactions, the transient absorption spectrum and reactivity of edaravone towards various oxidative radicals (OH, N, Br, SO, and CClO) are studied by pulse radiolysis techniques. The spectrum of its reaction with OH is quite different from those with the other oxidizing radicals. Moreover, to study the structure-activity-relationships, the rate constants of the reaction of some edaravone derivatives with OH are estimated by both buildup kinetics and competition method using carbonate ion and DMPO as competitors. The rate constant of derivatives having pyridine ring as a substituent by DMPO competition was estimated twice as high as that by buildup kinetics. This might be due to a possible interaction between these kind of derivatives and DMPO. We also calculated the heats of formation (HOF) using Gaussian03 program to identify the possible reaction mechanism of edaravone with OH.