CONICET | Buscador de Institutos y Recursos Humanos

Pterins belong to a family of heterocyclic compounds present in a wide range of living systems and participate in relevant biological functions. Under UV-A excitation (320?400 nm), pterins can fluoresce, undergo photooxidation and generate reactive oxygen species (ROS) [1]. In the presence of oxygen, pterin (Ptr) act as photosensitizer through type I (electron abstraction) and/or type II (1O2-mediated oxidation) mechanisms [2-3].The photosensitized degradations of the purine nucleotide and nucleoside, 2´-deoxyguanosine-5´-monophosphate (dGMP) and 2´-deoxyguanosine (dG), by Ptr were studied in neutral aqueous solutions upon UV-A irradiation (350 nm) at room temperature, under different experimental conditions. The photochemical reactions were followed by UV⁄vis spectrophotometry and HPLC.Photophysical properties of the triplet excited states of the sensitizer and the radical species formed in the process were characterized using laser flash photolysis. After analysis of the results, the mechanisms were proposed.Under anaerobic conditions, a recombination of the radicals occurred, and no consumption of the substrate (S, being S dGMP or dG, depending on the experiment) was registered. In the presence of O2, it was observed more consumption of the nucleotide or the nucleoside than saturated O2 solutions.In this case, there exist a competition between different reactions that includes type I and type II mechanisms for guanine. The main reaction is initiated by an electron transfer from the substrate to the triplet excited state of Ptr yielding the corresponding pair of radical ions (Ptr?− and S?+), with subsequent recovery of the photosensitizer by electron transfer from Ptr?− to O2. Finally, the substrateradical participates in later reactions to yield degradation products. Although the reaction between the guanine and 1O2 takes place, does not contribute significantly to the substrate consumption

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