Study of the photolysis of folic acid and 6-formylpterin in acid aqueous solutions

Folic acid and 6-formylpterin solutions of pH in the range 4.5-6.0 were photolysed at 350 nm at room temperature. The photochemical reactions were followed by UV-VIS spectrophotometry, thin layer chromatography (TLC) and high performance Liquid chromatography (HPLC). In the presence of oxygen, folic acid is photochemically cleavaged yielding 6-formylpterin and p-aminobenzoylglutamic acid. As the photolysis proceeds, 6-carboxypterin arises from 6-formylpterin, as observed when solutions only containing the latter compound are irradiated in the presence of oxygen. In the absence of oxygen, folic acid is not light-sensitive. However, when oxygen free solutions of 6-formylpterin are irradiated, a 'red intermediate' is observed, which is thermally oxidised producing 6-carboxypterin on admission of oxygen. The quantum yields of substrates disappearance and of photoproducts formation are reported. (C) 2000 Elsevier Science S.A. All rights reserved.