Radiation chemistry of carbohydrates. Part XVI. The contribution of OH radicals to the radiolysis of aqueous solutions

Abstract

Experiments using ⁶⁰Co γ-radiation show that the radiation degradation of D-glucose is chemically and kinetically different at 5 × 10^–4 M and at 5 × 10^–2 M. Scavenging experiments using potassium iodide, and the effects of solute concentration on product yields, support the view that abstraction by ·OH radicals initiates chemical change at ⩽ 5 × 10⁺³ M. Pulse-radiolysis experiments using 4-MeV electrons show that there is no significant reaction of e^–(aq) with carbohydrates. For the reaction e^–(aq)+D-glucose k₂ < 10⁷ mole^–1 sec.^–1 at 5 × 10^–3 M-D-glucose. A transient species with an absorption maximum at 2600–2700 Å is observed on pulsing, which decays by second-order kinetics within the solute range 5 × 10^–3 to 5 × 10^–1 M in solutions saturated with argon and nitrous oxide. Evidence is presented that the transient species is produced as a result of abstraction by the ·OH radical. Complete scavenging of the ·OH occurs at 5 × 10^–3 M. The further decomposition of D-glucose at higher concentrations is due to another process which may involve energy transfer from excited water molecules.