Polarographisches studium der photolyse und photoreduktion von riboflavin und 6,7-dimethyl-9-(formylmethyl)-isoalloxazin

Abstract

The photolysis and photoreduction of riboflavin and 6,7-dimethyl-9-(formylmethyl)-isoalloxazine (IV) was studied by polarographic methods under anaerobic conditions. A quantitative comparison of the products of photolysis of riboflavin and Compound IV revealed that in acid, neutral and slightly alkaline medium, lumichrome and the reduced form of Compound IV are the principal products. In addition, riboflavin gives rise to a small amount of the leuco form and minute amounts of 6,7-dimethyl-9-(2′-hydroxyethyl)-isoalloxazine and lumiflavin as side products. Formaldehyde is produced by photolytic decomposition of the side chain of Compound IV. The dependence of the velocity of photolysis on the structure of the isoalloxazine derivatives and on the medium was studied. The investigation of the photoreduction of riboflavin in the presence of certain amino acids (histidine, proline, sarcosine, cysteine, methionine, as well as EDTA) revealed the presence of products which can be reduced on the mercury electrode. In the presence of cysteine an equivalent amount of cysteine is formed during reduction of riboflavin. The published scheme of riboflavin photolysis and the photoreduction mechanism were discussed in the light of the experimental results obtained.