Pulse radiolysis investigations on the reactions of primary radiolytic species of water with atropine

Abstract

On pulse radiolysis of N2O saturated aqueous solutions of atropine, an optical absorption band (λmax at 320 nm,e=2.81·103 dm3·mol−1·cm−1) was observed, which is assigned to the product of reaction of OH radicals with the solute. This absorption decayed following second order kinetics with a rate constant of 4.5·108 dm3·mol−1·s−1. The rate constant for the reaction of OH radicals with atropine as estimated by following the build-up kinetics is 2.7·109 dm3·mol−1·s−1. The H atoms also reacted with this compound to produce a transient absorption band behaving similarly to the one observed in the case of reaction with OH radicals. The transient species formed in both cases is assigned to a radical derived by H atom abstraction by H/OH radicals from the parent compound. This radical was unreactive towards 2-mercaptoethanol. e aq − was found to react with atropine forming a transient band with λmax at 310 nm (e=3.55·103 dm3·mol−1). Its decay was also second order with a rate constant of 1.64·109 dm3·mol−1·s−1. The bimolecular rate constant for the reaction of e aq − with atropine as estimated from the decay of e aq − absorption at 720 nm is 3.9·109 dm3·mol−1·s−1. Specific one-electron oxidizing and reducing agents (such as Cl 2 − , Tl2+, SO 4 − and (CH3)2COH, CO 2 − , respectively) failed to oxidize or reduce this compound in aqoues solutions. The radical anion of atropine formed by its reaction with e aq − was found to reduce thionine and methyl viologen with bimolecular rate constant of 3.8·109 and 3.2·109 dm3·mol−1·s−1, respectively.