Abstract
Aqueous solutions of thiamine HCl and ascorbic acid have been photolysed by UV light at pH 1.0 to 11.0 in the presence and absence of riboflavin and the various photoproducts have been tentatively identified by thin-layer chromatography. The R-f values of thiamine HCl, riboflavin and ascorbic acid, and their photoproducts have been determined in several solvent systems. Thiamine HCl on photolysis gives rise to 2-methyl-4-amino-5-aminomethylpyrimidine, 2-methyl-4-amino-5-hydroxymethylpyrimidine, 4-methyl-5-(beta-hydroxyethyl) thiazole. alpha-aceto-gamma-mercaptopropanol, and thiochrome. Ascorbic acid is photolysed to dehydroascorbic acid and 23-diketogulonic acid. The photodcgradation of thiamine HCl is inhibited by riboflavin whereas that of ascorbic acid is promoted by riboflavin as indicated by the intensity of the spots of their respective photoproducts During the photolysis of thiamine HCl and ascorbic acid, riboflavin itself is photolysed to formyimethylflavin, lumichrome, lumiflavin. carboxymethylflavin, and unknown products. The nature and amounts of the various products formed depend upon the pH of photolysis. A pH range around 5.0 has been suggested to achieve greater stability of thiamine HCl and ascorbic acid in vitamin preparations in the presence of riboflavin.