Photooxidation of Pterin in Aqueous Solutions: Biological and Biomedical Implications

F.M. CABRERIZO; M.L. DÁNTOLA; A.H. THOMAS; C. LORENTE; A.M. BRAUN; E. OLIVEROS; A.L. CAPPARELLI

Chemistry and Biodiversity

Año: 2004 vol. 1 p. 1800 - 1811

1612-1872

Studies of the photochemical reactivity of pterin (2-aminopteridin-4(3H)-one; PT) in acidic (pH 5.0±6.0) and alkaline (pH 10.2±10.8) aqueous solutions have been performed. The photochemical reactions were followed by UV/VIS spectrophotometry, thin layer chromatography (TLC), high-performance liquid chromatography (HPLC), and an enzymatic method for H2O2 determination. PT is not light-sensitive in the absence of molecular oxygen, but it undergoes photooxidation in the presence of O2 , yielding several nonpteridinic products. The quantum yields for PT disappearance were found to be 8.2 (0.6)104 and 1.2 (0.2)103 in acidic and alkaline media, respectively. H2O2 was detected and quantified in irradiated solutions of PT; and its importance from a biomedical point of view is discussed. The rate constant of the chemical reaction between singlet oxygen (1O2) and PT was determined to be 2.5 (0.2)105 l mol1 s1 in all medium, and the role of 1O2 in the photooxidation of pterin was evaluated.