Photoinduced Formation of Reactive Oxygen Species from the Acid Form of 6‐(Hydroxymethyl)pterin in Aqueous Solution

Abstract

AbstractThe 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 (O$\rm{_2^{ \bullet - } }$) and hydrogen peroxide (H2O2). When 1a is exposed to UV‐A radiation, the intermediates 4 and 4′ are formed reacting with O2 to yield 6‐formylpterin (FPT; 5) and 6‐carboxypterin (CPT; 6) under formation of O$\rm{_2^{ \bullet - } }$ 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 (ΦΔ) 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).