INVESTIGADORES
THOMAS Andres Hector
congresos y reuniones científicas
Título:
Purine and Pyrimidine Nucleotides Photosensitization by Pterin
Autor/es:
MARIANA P. SERRANO; CAROLINA LORENTE; FAUSTINO E. MORÁN VIEYRA; CLAUDIO D. BORSARELLI; ANDRÉS H. THOMAS
Reunión:
Congreso; 16th International Congress on Photobiology; 2014
Institución organizadora:
International Union of Photobiology
Resumen:
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) acts as a photosensitizer through type I (electron abstraction) and/or type
II (1O2-mediated oxidation) mechanisms [2-3].
The
photosensitized degradations of purine and pyrimidine nucleotides 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, and the photoproducts were
analyzed by means of electrospray ionization mass spectrometry. Photophysical
properties of the triplet excites states of the sensitizer were characterized
using laser flash photolysis. After analysis of the results, reaction
mechanisms were proposed.
Under
anaerobic conditions, for purine nucleotides, a recombination of the radicals
occurred, and no consumption of the nucleotide was registered. 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 are similar to those of Ptr itself.
In the
presence of O2, it was observed more consumption of the nucleotides
than in anaerobic condition. In this case, there exist a competition between
different reactions that includes type I and type II mechanisms for guanine
nucleotide. For the others, which do not react with singlet oxygen, the
reaction is initiated by an electron transfer from the nucleotide to the
triplet excited state of the pterin yielding the corresponding pair of radical
ions (Pt?− and dNMP?+), with successive photosensitizer
recovery by electron transfer from Pt?− to O2. Finally,
dNMP?+ participates in subsequent reactions to yield degradation
products.
Acknowledgments CONICET for
the phD scholarship.
[1] Lorente, C.; et. al.; Acc. Chem. Res. 2006, 39,
395.
[2] Petroselli, G.; et. al.; J.
Am. Chem. Soc. 2008, 130, 3001.
[3] Petroselli, G.; et. al.; Org. Biomol.Chem. 2007, 5,
2792.