Singlet Oxygen Production and Quenching by Pterins

M. LAURA DÁNTOLA; ANDRÉS H. THOMAS; ANDRÉ M. BRAUN; ESTHER OLIVEROS; CAROLINA LORENTE

Saint Petersburg, Florida, USA

Congreso; IXX Inter-American Photochemical Society Winter Conference; 2009

Inter-American Photochemical Society

Pterins belong to a family of heterocyclic compounds present in a wide range of living systems and participate in relevant biological functions. Interest in the photochemistry and photophysics of this group of compounds1 has increased since the participation of pterin derivatives in different photobiological processes has been suggested or demonstrated in recent decades. Pterins (PTs) are derived from 2-aminopteridin-4(3H)-one or pterin. The most common pterin derivatives are 6-substituted compounds. PTs can exist in different oxidation states and be divided into two classes according to this property: (a) oxidized or aromatic PTs and (b) reduced PTs. Within the latter group, 7,8-dihydropterins and 5,6,7,8-tetrahydropterins are the most important derivatives due to their biological activity. Oxidized and reduced PTs accumulate in the white skin patches of patients affected by vitiligo.2 In this disease protection of the skin against UV radiation fails due to the lack of melanin. Pterins (PTs) are derived from 2-aminopteridin-4(3H)-one or pterin. The most common pterin derivatives are 6-substituted compounds. PTs can exist in different oxidation states and be divided into two classes according to this property: (a) oxidized or aromatic PTs and (b) reduced PTs. Within the latter group, 7,8-dihydropterins and 5,6,7,8-tetrahydropterins are the most important derivatives due to their biological activity. Oxidized and reduced PTs accumulate in the white skin patches of patients affected by vitiligo.2 In this disease protection of the skin against UV radiation fails due to the lack of melanin. Singlet molecular oxygen (1O2), the lowest electronic excited state of molecular oxygen, is an important oxidizing species in chemical processes and one of the main activated species responsible for the damaging effects of light on biological systems (photodynamic effects).3 This activated metastable state is much more reactive than the ground triplet state and has been attracting interest in both practical and fundamental aspects.4 Photosensitization is primarily responsible for the production of 1O2 in vivo.5 The photochemical production of 1O2 by PTs in aqueous solution was studied by direct analysis of the weak 1O2 near-infrared luminescence, produced upon excitation with continuous UV-A radiation.6,7,8 High quantum yields of 1O2 production (ΦΔ) were measured for most oxidized PT derivatives. The nature of the substituent at position 6 and the pH considerably affect the capacity of PTs to produce 1O2. In contrast, all studied dihydropterins do not produce 1O2 under UV-A irradiation. On the other hand, the quenching of 1O2 by PTs was studied.8,9 If a biological compound is able to deactivate 1O2 efficiently by means of physical quenching, such a compound may have a protective role against 1O2 in vivo and very likely against other reactive oxygen species. In contrast, an efficient chemical reaction with 1O2 may be beneficial or harmful to biological systems depending on the nature of the oxidized products. Therefore, the study of the reactivity of 1O2 with biomolecules is an important tool to analyze their antioxidant capability. Determination of the rate constants of 1O2 physical quenching and chemical reaction with 1O2 (kq and kr, respectively) allows evaluation of the efficiencies of these processes. Products identification provides information to elucidate oxidation mechanisms and discuss potential effects in vivo. The values of kt of the dihydropterin derivatives are strikingly larger than those reported for oxidized pterin derivatives, indicating that the dihydropyrazine ring is much more efficient in quenching 1O2 than the pyrazine one. The deactivation of 1O2 by dihydropterins is mainly a chemical process. In contrast, oxidized PTs are predominantly 1O2 physical quenchers. The values of kt of the dihydropterin derivatives are strikingly larger than those reported for oxidized pterin derivatives, indicating that the dihydropyrazine ring is much more efficient in quenching 1O2 than the pyrazine one. The deactivation of 1O2 by dihydropterins is mainly a chemical process. In contrast, oxidized PTs are predominantly 1O2 physical quenchers. The values of kt of the dihydropterin derivatives are strikingly larger than those reported for oxidized pterin derivatives, indicating that the dihydropyrazine ring is much more efficient in quenching 1O2 than the pyrazine one. The deactivation of 1O2 by dihydropterins is mainly a chemical process. In contrast, oxidized PTs are predominantly 1O2 physical quenchers. On the other hand, the quenching of 1O2 by PTs was studied.8,9 If a biological compound is able to deactivate 1O2 efficiently by means of physical quenching, such a compound may have a protective role against 1O2 in vivo and very likely against other reactive oxygen species. In contrast, an efficient chemical reaction with 1O2 may be beneficial or harmful to biological systems depending on the nature of the oxidized products. Therefore, the study of the reactivity of 1O2 with biomolecules is an important tool to analyze their antioxidant capability. Determination of the rate constants of 1O2 physical quenching and chemical reaction with 1O2 (kq and kr, respectively) allows evaluation of the efficiencies of these processes. Products identification provides information to elucidate oxidation mechanisms and discuss potential effects in vivo. The values of kt of the dihydropterin derivatives are strikingly larger than those reported for oxidized pterin derivatives, indicating that the dihydropyrazine ring is much more efficient in quenching 1O2 than the pyrazine one. The deactivation of 1O2 by dihydropterins is mainly a chemical process. In contrast, oxidized PTs are predominantly 1O2 physical quenchers. The values of kt of the dihydropterin derivatives are strikingly larger than those reported for oxidized pterin derivatives, indicating that the dihydropyrazine ring is much more efficient in quenching 1O2 than the pyrazine one. The deactivation of 1O2 by dihydropterins is mainly a chemical process. In contrast, oxidized PTs are predominantly 1O2 physical quenchers. The values of kt of the dihydropterin derivatives are strikingly larger than those reported for oxidized pterin derivatives, indicating that the dihydropyrazine ring is much more efficient in quenching 1O2 than the pyrazine one. 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[9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [6] Thomas, A. H.; Lorente, C.; Capparelli, A. L.; Martínez, C. G.; Braun, A. M.; Oliveros, E. Photochem. Photobiol. Sci. 2003, 2, 245-250. [7] Cabrerizo, F. M.; Lorente, C.; Vignoni, M.; Cabrerizo, R.; Thomas, A. H.; Capparelli, A. L. Photochem. Photobiol. 2005, 81, 793-801. [8] Dántola, M. L.; Thomas, A. H.; Braun, A. M.; Oliveros, E.; Lorente, C. J. Phys. Chem. A 2007, 111, 4280-4288. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [8] Dántola, M. L.; Thomas, A. H.; Braun, A. M.; Oliveros, E.; Lorente, C. J. Phys. Chem. A 2007, 111, 4280-4288. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [7] Cabrerizo, F. M.; Lorente, C.; Vignoni, M.; Cabrerizo, R.; Thomas, A. H.; Capparelli, A. L. Photochem. Photobiol. 2005, 81, 793-801. [8] Dántola, M. L.; Thomas, A. H.; Braun, A. M.; Oliveros, E.; Lorente, C. J. Phys. Chem. A 2007, 111, 4280-4288. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [8] Dántola, M. L.; Thomas, A. H.; Braun, A. M.; Oliveros, E.; Lorente, C. J. Phys. Chem. A 2007, 111, 4280-4288. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [3] Briviba, K.; Klotz, L. O.; Sies, H. Biol. Chem. 1997, 378, 1259-1265. [4] Braun, A. M.; Maurette, M. T.; Oliveros, E. Photochemical Technology; translated by Ollis, D., and Serpone, N.; Wiley: Chichester, 1991; pp 445-499. [5] Cadenas, E. Biochemistry of oxygen toxicity. Annu. Rev. Biochem. 1989, 58, 79-110. [6] Thomas, A. H.; Lorente, C.; Capparelli, A. L.; Martínez, C. G.; Braun, A. M.; Oliveros, E. Photochem. Photobiol. Sci. 2003, 2, 245-250. [7] Cabrerizo, F. M.; Lorente, C.; Vignoni, M.; Cabrerizo, R.; Thomas, A. H.; Capparelli, A. L. Photochem. Photobiol. 2005, 81, 793-801. [8] Dántola, M. L.; Thomas, A. H.; Braun, A. M.; Oliveros, E.; Lorente, C. J. Phys. Chem. A 2007, 111, 4280-4288. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [8] Dántola, M. L.; Thomas, A. H.; Braun, A. M.; Oliveros, E.; Lorente, C. J. Phys. Chem. A 2007, 111, 4280-4288. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [7] Cabrerizo, F. M.; Lorente, C.; Vignoni, M.; Cabrerizo, R.; Thomas, A. H.; Capparelli, A. L. Photochem. Photobiol. 2005, 81, 793-801. [8] Dántola, M. L.; Thomas, A. H.; Braun, A. M.; Oliveros, E.; Lorente, C. J. Phys. Chem. A 2007, 111, 4280-4288. [9] Cabrerizo, F. M.; Dántola, M. L.; Petroselli, G.; Capparelli, A. L.; Thomas, A. H.; Braun, A. M.; Lorente, C.; Oliveros, E. Photochem. Photobiol. 2007, 83, 526–534. Photobiol. 2007, 83, 526–534. [9] Cabrerizo, F. M.; Dántola, M. 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