Photooxidation of Pterin in Aqueous Solutions: Biological and Biomedical Implications

FRANCO M. CABRERIZO; MARÍA L. DÁNTOLA; ANDRÉS H. THOMAS; CAROLINA LORENTE; ANDRÉ M. BRAUN; ESTHER OLIVEROS; ALBERTO 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)x10-4 and 1.2 (±0.2)x10-3 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)x105 l mol-1 s-1 in alkaline medium, and the role of 1O2 in the photooxidation of pterin was evaluated.