Structure and Chemical Characteristics of Dehydro-L-Ascorbic Acid in Solutions.

L-Ascorbic acid (ASA) plays an important role in food and biological systems as an electron donor, and in the electron-donating process, ASA itself is generally oxidized to dehydro-L-ascorbic acid (DHA). The structure of DHA was reconfirmed to be monohydrated bicyclic structure in an aqueous solution. It was also clarified that DHA had the solvated bicyclic structure in methanol and ethanol solutions, and in these cases, the enantiomers were formed by the solvation of the C2 carbonyl group. When these solvated bicyclic DHA were dissolved in water, the solvent molecule on the solvated C2 carbonyl group was very easily replaced with a water molecule. From the results of MOPAC calculations, the heat of formation of C2 hydrated bicyclic DHA was estimated to be -299.2 kcal/mol, and DHA was clarified to be considerably stabilized by hydration. Furthermore, it was indicated that bicyclic DHA had more compact and less polar structure than ASA.