A Radiation-Chemical and Quantum-Chemical Study of Ascorbic Acid Interaction with α-Hydroxyethyl Radicals

The effect of ascorbic acid and its analogue 5,6-O-isopropylidenyl-2,3-O-dimethylascorbic acid (I), which has been synthesized for the purpose and does not contain mobile hydrogen atoms, on the formation of the products of continuous radiolysis of deaerated ethanol and its aqueous solutions has been studied. The ionization potentials, the molecular orbital energies, the enthalpies of homolytic dissociation of C-H and O-H bonds, and the enthalpies of H atom addition to the C=O group of the test compounds have been calculated by ab initio methods. The array of the experimental and calculated theoretical data suggests that both ascorbic acid in the undissociated form and compound I can oxidize alpha-hydroxyethyl radicals, whereas the monoanion of ascorbic acid acts as a reducing agent in the reactions with these transient radicals. The reduction of alpha-hydroxyethyl radicals in aqueous solutions by the ascorbic acid monoanion can follow both the hydrogen transfer and electron transfer mechanisms.