Photophysical Behaviour of Lumazine

M. PAULA DENOFRIO; ANDRÉ BRAUN; ESTHER OLIVEROS; ANDRÉS H. THOMAS; CAROLINA LORENTE

Los Cocos, Córdoba, Argentina

Conferencia; 9a Conferencia Latinoamericana de Fisicoquímica Orgánica (CLAFQO-9); 2007

2,4-dihydroxylumazine (LU) belongs to a group of significant compounds called pteridines. Pteridines include two groups: pterins and lumazines. LU is present in cells as a cofactor of enzimes involved in hydroxylation, methyl-transfer, electron-transfer. These compounds present high fluorescence and are presumed to be good sensitizer of singlet oxygen. Light sensitivity of pteridins is known since several decades (1). Interest in photochemistry and photophysics of this group of compounds has been shown since participation of pteridins in different photobiological processes has been proven or suggested. Pteridins are also interesting as possible photosensitizers in photochemical processes that take place in organisms exposed to UV-A radiation; e.g., pterins participate in photochemical reactions that induce DNA damage (2,3). The pKa of this equilibrium is around 8. The studies were performed at pH 5.5 and 10.5 in order to study only one acid-base form In this work, we described the emission properties of LU in alkaline and acid media (emission spectra, fluorescence quantum yields (FF) and fluorescence lifetimes (tF)) The FF is pH dependent, being higher for the alkaline form. The maxima of the excitation and of the absorption spectra are similar, however, the intensity ratio of the high energy band to that of the low energy band is different. We also report the efficiency of singlet oxygen production (FD) and its quenching. The FD are also pH dependent: the acid form is a good 1O2 sensitizer, whereas the basic form is a very poor 1O2 sensitizer. 1.Galland P., Senger, H, 1988,Photochem. Photobiol., 48, 811-820. 2. Ito, K., S. Kawanishi, 1997, Biochemistry 36, 1774-1781. 3 Lorente, C., A. H. Thomas, L. S. Villata, D. Hozbor, A. Lagares, A. L. Capparelli, 2000, Pteridines 11, 100-105.