Generation of Reactive Oxygen Species during the Photolysis of 6-(Hydroxymethyl)pterin in Alkaline Aqueous Solutions

✍ Scribed by Franco M. Cabrerizo; Andrés H. Thomas; Carolina Lorente; María L. Dántola; Gabriela Petroselli; Rosa Erra-Balsells; Alberto L. Capparelli

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: German
• Weight: 234 KB
• Volume: 87
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200490032

✦ Synopsis

Photochemical studies of the reactivity of 6-(hydroxymethyl)pterin ( 2-amino-6-(hydroxymethyl)pteridin-4(1H)-one; HPT) in alkaline aqueous solutions (pH 10.2 ± 10.8) at 350 nm and room temperature were performed. The photochemical reactions were followed by UV/VIS spectrophotometry, thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and an enzymatic method for H 2 O 2 determination. In the presence of O 2 , 6-formylpterin ( 2-amino-3,4-dihydro-4-oxopteridine-6-carboxaldehyde; FPT) was the only photoproduct detected. In the absence of O 2 , we observed a compound with an absorbance maximum at 480 nm, which was oxidized very rapidly by O 2 in a dark reaction to yield FPT. The quantum yields of substrates disappearance and of photoproducts formation were determined. The formation of H 2 O 2 during photooxidation was monitored, and the number of mol of H 2 O 2 released per mol of HPT consumed corresponded to a 1 : 1 stoichiometry. HPT was also investigated for efficiency of singlet-oxygen ( 1 O 2 ) production and quenching in aqueous solution. The quantum yield of 1 O 2 production (F D 0.21 AE 0.01) was determined by measurements of the 1 O 2 luminescence in the near-IR (1270 nm) upon continuous excitation of the sensitizer. The rate constant of 1 O 2 total quenching by HPT was determined (k t 3.1 ¥ 10 6 m À1 s À1 ), indicating that this compound was able to quench 1 O 2 . However, 1 O 2 did not participate in the photooxidation of HPT to FPT.