Free Radicals in the Auto-Oxidation of Ascorbic Acid.

Nature of serum ascorbate radical and its quantitative estimation.

“…The findings that the ascorbate radical has a g value of 2.0054 and hyperfine splitting constants of 1.83-1.84 gauss are well agreed with those of Lagercrantz (1964) and Laroff et al (1972).…”

The oxidation of ascorbic acid and hydroquinone by perhydroxyl radicals. A flash photolysis study

“…The rate constant of semiquinone radical disproportionation is extremely high at low pH, 2k,, = 1.2 x lo9 M -I s-I (21) and without knowledge of kt, we could not compare the rates of the reactions [12] and [13]. Therefore the elementary rate constant of the reaction [14] Addition of 2 x M quinone to the solution containing 2 x M QH, and 0.2 M H 2 0 2 at pH 2.5 totally subdued the hydroquinone consumption normally observed in the absence of quinone after a flash. However, several drops of concentrated HCIO, added to the solution restored the process of QH, oxidation under irradiation; the final pH in the system was 1.05.…”

“…The rate constant of the disproportionation of A-' radicals, k,, is known at different pH values (14). M, we did not observe any change of absorbance at 360 nm in a pH region from 4.2 to 7.5, therefore in the course of AH, consumption [A-'1 did not exceed 4 x M. Using the above mentioned values of k, and the experimentally determined k,,, as k, in accordance with Scheme (b), one can see that relation [6] is not fulfilled.…”

“…Quintuply distilled water was used for ail experiments. Control experiments, where optical absorption of the solution was recorded vs. time in the absence of flash light, showed that the spontaneous oxidation of AH, and QH, by 0, or H 2 0 Z was a negligibly slow process compared to the reductants consumption under irradiation (14).…”

Some EPR Signals in Tumour Tissue

“…Ascorbic acid assignment is made for the following reasons: (a) The ascorbyl radical, which has recently been shown to exist as the anion with the unpaired electron delocalized over a highly conjugated tricarbonyl system (Laroff, Fessenden and Schuler, 1972), gives a spectrum with a g value of 2-0052, consisting of a doublet of triplets (Lagercrantz, 1964) with splittings of 1-76 G and 0-19 G and an additional doublet splitting of 0 07 G (Laroff et al, 1972). Although it has not been possible to demonstrate any structure in the doublet from tumour tissue, the line width observed does not rule out unresolved fine structure.…”