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 (λ_max 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 λ_max at 310 nm (ε=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.