engleski

Dependence of the relative conformer stability on the ionization state of vitamin c

The relative stability of various conformers of vitamin C were calculated as a function of the ionization state of the molecule. Full geometry optimizations and frequency calculations were performed at the B3LYP/6-31+G(d) level of theory. Protonated ascorbic acid (charge = +1), ascorbic acid (0), ascorbate anion (-1), ascorbate dianion (-2) and dehydroascorbic acid (0) were considered in this comparative study. In the case of ascorbic acid the largest energy difference between conformers is calculated to be less than 6 kcal/mol, while in the case of ascorbate dianion this energy difference is larger than 12 kcal/mol. The stability sequence of the nine staggered conformers of the side chain (generated by rotation about two dihedral angles a and b) is also influenced by the ionization form of vitamin C.

ascorbic acid; ascorbate; dft; conformation

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