Premium
Photochemical Behavior of Folic Acid in Alkaline Aqueous Solutions and Evolution of Its Photoproducts
Author(s) -
Thomas Andrés H.,
Suárez Gustavo,
Cabrerizo Franco M.,
García Einschlag Fernando S.,
Martino Raúl,
Baiocchi Claudio,
Pramauro Edmondo,
Capparelli Alberto L.
Publication year - 2002
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(200208)85:8<2300::aid-hlca2300>3.0.co;2-b
Subject(s) - chemistry , aqueous solution , reaction rate constant , photodissociation , singlet oxygen , photochemistry , high performance liquid chromatography , kinetics , spectrophotometry , amino acid , decarboxylation , chromatography , oxygen , organic chemistry , catalysis , biochemistry , physics , quantum mechanics
The photolysis of folic acid (= N ‐(4‐{[(2‐amino‐1,4‐dihydro‐4‐oxopteridin‐6‐yl)methyl]amino}benzoyl)‐ L ‐glutamic acid) in alkaline aqueous solution (pH 10.0–11.0) was carried out at 350 nm at room temperature and monitored by UV/VIS spectrophotometry, anal. and prep. thin‐layer chromatography (TLC), and high‐performance liquid chromatography (HPLC, HPLC/MS). The folate species underwent at least two independent photo‐oxidation pathways, which were not observed when the acid form was photolyzed at pH<7. The presence of O 2 was essential in these oxidation pathways. Evidence for the role of singlet oxygen was established. In one of the pathways, the folate underwent cleavage, yielding 6‐formylpterin (=2‐amino‐1,4‐dihydro‐4‐oxopteridine‐6‐carboxaldehyde) and (4‐aminobenzoyl)glutamic acid as photoproducts. The other pathway yielded a new photostable product A of molecular mass 455, which could be isolated and stored in acidic or neutral aqueous solution. However, A was rather unstable in alkaline media undergoing a thermal reaction to a product B of lower molecular mass (427). The kinetics of this thermal reaction was analyzed with a stopped‐flow spectrophotometer. A linear dependence of the first‐order rate constant with the OH − concentration was observed. The corresponding bimolecular rate constant was 1.1 M −1 s −1 . The quantum yields of substrate consumption and of photoproduct formation were determined. The here‐reported photochemical behavior of folate solutions departs from results in acid media, where phototransformation proceeded via the cleavage of the acid form into 6‐formylpterin and (4‐aminobenzoyl)glutamic acid as the first major photoproducts, and where no thermal reactions were observed.