Degradation of vitamin C: Theoretical

The L-enantiomer [(4R,5S)-AA, 1 Scheme 1a] of ascorbic acid (meaning without scurvy ,the disease caused by vitamin C deficiency) is called vitamin C. [1]. Vitamin C has two chiralcenters with four steroisomers (two enantiomers and two diasteromers). The L-ismomersassumed to be beneficial for human, but very little is known about the other three isomers [2].The ascorbate monoion possesses both acid and base properties [3 ].Theoretically,calculations have confirmed that the monoanion obtained in the gas phase from deprotonationat O3 is the most stable (in the ground state) of ascorbic acid monoanions [4, 5].Recently, Dabbagh and coworkers studied the theoretical study of isomerization at C4 and C5anions of ascorbic acid stereoisomers [6]. It was concluded that de-protonation at C5 site ofVC leads to the ring opening and isomerization of the L-form to D-form [7]. VC instabilitywas shown to relate to isomerization (loss of optical activity) of the L-enantiomer either to Denantiomer(racemization), degradation to undesired products, and/or tautomerization.