Hideo Horii

A theoretical study on the mechanism of oxidation of L-ascorbic acid

The oxidation of L-ascorbic acid (vitamin C) to dehydroascorbic acid is investigated by ab initio MO calculations. Their geometries together with intermediate species are optimized at the STO-3G level. The electron and spin densities are obtained with the 4-31G basis set. The five-membered (γ-lactone) ring is found to be planar during the oxidation process. Neutral and anion radicals are of the similar geometry but are of the different spin-density distribution. The stability of the ascorbate ion and the ascorbate anion radical is attributed to the ‘pseudo-aromaticity’ involved. The energy variation of the oxidation process of L-ascorbic acid is compared with that of triose reductone which is the simplest molecule having the same functional groups as the former compound.

Oxidation intermediates of borohydride and tetraphenylborate ions in aqueous solutions obtained by pulse radiolysis

Absorption spectra of one-electron oxidized intermediates (the H4B· and the Ph4B· radicals) were observed upon the oxidation of H4B– and Ph4B– by the azide radical (N3·), Br2[graphic omitted], or (SCN)2[graphic omitted] in plus-irradiated solutions; the spectra have absorption maxima at 400 nm, Iµ= 1800 dm3 mol–1 for H4B· and at 335 nm, Iµ= 8600 dm3 mol–1 for cm–1 for Ph4B·.