Formation of reactive oxygen species during the photolysis of 6-hydroxymethylpterin in acid aqueous solution

A.H. THOMAS; R. CABRERIZO; M. VIGNONI; R. ERRA-BALSELLS; F.M. CABRERIZO*; A.L. CAPPARELLI*

HELVETICA CHIMICA ACTA

Año: 2006 vol. 89 p. 1090 - 1104

0018-019X

The photochemistry of 6-(hydroxymethyl)pterin (HPT; 1) in aqueous solution (pH 5-6) was investigated by irradiation at 350 nm at room temperature. The photochemical reactions of the acidic form 1a were followed by UV/VIS spectrophotometry, thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and enzymatic methods for the determination of the superoxide anion radical (O2- ) and hydrogen peroxide (H2O2). When 1a is exposed to UV-A radiation, the intermediates 4and 4’ are formed reacting with O2 to yield 6-formylpterin (FPT; 5) and 6-carboxypterin (CPT; 6) under formation of O2- and H2O2 (Scheme 3). The quantum yields of the disappearance of HPT (1a) and of the formation of the photoproducts 5 and 6 were determined. HPT was investigated for its efficiency in singlet-oxygen (1O2) production in acidic aqueous solution. The corresponding quantum yield of 1O2 production (FD) was 0.15+/-0.02, as measured by the 1O2 luminescence in the near-IR (1270 nm) upon continuous excitation of the sensitizer. However, 1O2 does not participate in the actual photooxidation of HPT (1a) to FPT (5) and CPT (6).