Coupled oxidation of ascorbic acid and haemochromogens

Abstract

Ascorbic acid and hemochromogens undergo a coupled oxidation in presence of O2. Pyridine hemochromogen is transformed to verdohemochromogen; ascorbic acid is converted to dehydroascorbic acid. The reaction was studied quantitatively, the expts. being done in Thunberg tubes with hand shaking. Hematin determinations were made by reducing with Na2SsO4 and spectrocolorimetric comparison with a standard hemochromogen solution. Ascorbic acid was detd. by I2 titration of trichloroacetic acid filtrates. The temp. coefficient of hematin oxidation is greater than that of acetic acid. The rate of ascorbic acid oxidation is proportional to O2 pressure and initially is roughly proportional to original concs, of both components. Ascorbic acid is protected by glutathione, which reduces dehydroascorbic acid. The velocity of hematin oxidation is independent of O2 pressure. It is initially proportional roughly to original concns. of both components, but in later stages is independent of ascorbic acid concn. Both oxidations are partly inhibited by cyanide. Nicotine and pilocarpine hemochromogen also undergo the reaction. Hb reacts slowly. It is possible that the reaction may help to explain physiological bile pigment formation.