A MOLECULAR-ORBITAL STUDY ON THE REACTIVITY OF L-ASCORBIC-ACID TOWARDS OH RADICAL

The reaction between L-ascorbic acid (AAH2) and OH radical has been investigated theoretically. The addition site on AAH2 and AAH- is found to be the olefinic carbon adjacent to the carbonyl group, with much more distinct selectivity for AAH-. Dehydration is found to occur readily not from the neutral .OH adduct AAH2OH., but from the anion adduct, AAHOH.-, which leads to formation of the most probable key intermediate radical 17 (ascorbate anion radical). The parent molecule of AAH2, triose reductone TRH2 (2,3-dihydroxyprop-2-enal), undergoes 'OH addition and dehydration in a similar manner to AAH2. The addition site has been confirmed by comparison of MO energies for four possible transition states of the TRH2 (ab initio and MNDO) and AAH2 (MNDO) systems. The importance of the conjugate bases, AAH- and TRH-, for yielding the key radicals is suggested.