Radiation chemistry of carbohydrates. Part XIX. Yields of trapped electrons and radicals in γ-irradiated, frozen, concentrated, aqueous solutions of sugars

Abstract

Trapped electron (e_t^–) and sugar radical yields in aqueous carbohydrate matrices γ-irradiated at 77 K have been determined using photbleaching and electron scavenging methods. Maximum values of Ge_t^–= 2·2 are found at 60% w/w solute and G(sugar radicals)= 2·3 at this solute concentration. Photobleaching results in reaction of the trapped electrons with the sugar to give almost an equivalent yield of sugar radicals and makes this method, therefore, unreliable for determining Ge_t^–. Conversion of radiation induced electrons into hydrogen atoms using H₂SO₄ doubles G(sugar radicals) at 60% w/w solute. From the variations in e_t^– and radical yields with carbohydrate concentration in acidic and neutral ices, an increase in the ‘glassiness’ of the ices can be monitored as the solute content is increased above ca. 40% w/w. An increase in the yield of e_t^– occurs here due to an increase in the number of suitable traps. Optical absorption spectra of e_t^– have been recorded at 77 K in frozen, aqueous D-glucose, D-fructose, and sucrose glasses; λ_max. decreases linearly with increasing sugar concentration, giving by extrapolation λ_max.(glassy ice)= 670–690 nm and λ_max.(pure sugar glass)= 485, 505, and 516 nm for the three sugars.