Photoinduced generation of H2O2 and O2- by 6-formylpterin in aqueous solutions

PETROSELLI GABRIELA; BARTSCH JONAS M.; THOMAS ANDRÉS H.

PTERIDINES

INT SOC PTERIDINOLOGY

Año: 2006 vol. 17 p. 82 - 89

0933-4807

6-Formylpterin is one of the oxidized pterins that accumulate in the white skin patches of patients affected by vitiligo. Studies of photoinduced generation of hydrogen peroxide (H2O2) and superoxide anion radical (O2.-) by formylpterin in acidic and alkaline aqueous solutions at 350 nm and room temperature have been performed. The photochemical processes were followed by UV-VIS spectrophotometry and enzymatic methods for H2O2 and O2.- determination. When formylpterin is irradiated a red intermediate, that has been proposed to be 6-carboxy- 5,8-dihydropterin, is generated in an O2-independent process. In the presence of air that intermediate reacts with O2 to yield H2O2 and 6-carboxypterin. In anaerobic conditions it undergoes a thermal O2-independent reaction which leads to a non-identified product without generation of H2O2. The rate constants of such a process were determined to be 0.011 min-1 and 0.044 min-1 at pH 5.4 and 10.5, respectively. (O2.-), is also generated during photooxidation of formylpterin, probably as a consequence of the electron transfer from the red intermediate to O2. The biomedical importance of photoinduced generation of H2O2 and O2.-  is discussed.