Purine and pyrimidine nucleotides photosensitization by pterin

MARIANA PAULA SERRANO; CAROLINA LORENTE; FAUSTINO E. MORÁN VIEYRA; CLAUDIO D. BORSARELLI; ANDRÉS H. THOMAS

Córdoba

Congreso; 16th International Congress on Photobiology; 2014

International Union of Photobiology

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 photosensitization reaction of purine and pyrimidine nucleotides by pterin was 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. Photoproducts were analyzed by means of electrospray ionization mass spectrometry. Photophysical properties of the the triplet excites states of the sensitizer was characterized using laser flash photolysis. The mechanistic analysis was done, and a mechanism for the photosensitization reactions was proposed. Under anaerobic conditions, for purine nucleotides, a recombinations of the radicals to yield the ground state Ptr and purine nucleotides molecules occurred, and no consumption of the nucleotide was registered by means of HPLC. On the other hand, for pyrimidine nucleotides, the formation of an adduct between the substrate and the sensitizer was observed. The fluorescence properties of this adduct presents fluorescence properties similar to the Ptr itself. In the presence of O2,it was observed more consumption of the nucleotides than in anaerobic condition. In this case, exists a competition between different reactions, that includes type I and type II mechanisms for guanine nucleotide. For the others nucleotides, which don´t react with singlet oxygen, there is a competition between the triplet excited estate of Ptr and Ptr radical anion by O2, to yield oxidized products. Acknowledgments CONICET for the phD schoralship. [1] Lorente, C.; Thomas, A. H.; Acc. Chem. Res. 2006, 39, 395. [2] Petroselli, G.; Dántola, M. L.; Cabrerizo, F. M.; Capparelli, A. L.; Lorente, C.; Oliveros, E.; Thomas, A. H.; J. Am. Chem. Soc. 2008, 130, 3001. [3] Petroselli, G.; Erra-Balsells, R.; Cabrerizo, F. M.; Lorente, C.; Capparelli, A. L.; Braun, A. M.; Oliveros, E.; Thomas, A. H.; Org. Biomol.Chem. 2007, 5, 2792.