Production and quenching of reactive oxygen species
Under UV-A excitation (320–400 nm), aromatic pterins (Pt) can generate reactive oxygen species (ROS), as a consequence of both energy- and electrontransfer processes from their triplet excited state. Quantum yields of singlet oxygen (1O2) production depend largely on the nature of the substituents on the pterin moiety, on the oxidation state of the pyrazine ring and on the pH. Formation of the superoxide anion by electron transfer between the pterin radical anion and molecular oxygen leads to the production of significant amounts of hydrogen peroxide (H2O2) by disproportionation. Dihydropterins (H2Pt) do not produce 1O2 but are oxidized by this species with high rate constants yielding pterins as well as H2O2. In contrast to aromatic derivatives, H2Pt are oxidized by H2O2, and rates and products strongly depend on the nature of the substituents on the H2Pt moiety.
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