Singlet Oxygen (1O2) Quenching by Dihidropterins

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

JOURNAL OF PHYSICAL CHEMISTRY A

Año: 2007 vol. 111 p. 4280 - 4288

1089-5639

Pterins belong to a class of heterocyclic compounds present in a wide range of living systems. They participate in relevant biological functions and are involved in different photobiological processes. Dihydropterins are one of the biologically active forms of pterins. The photoinduced production and quenching of singlet oxygen (1O2) by a series of dihydropterins (7,8-dihydrobiopterin (DHBPT), 7,8-dihydroneopterin (DHNPT), 6-formyl-7,8-dihydropterin (FDHPT), sepiapterin (SPT), 7,8-dihydrofolic acid (DHFA), and 7,8-dihydroxanthopterin (DHXPT)) in aqueous solution at physiological pH (~ 7) were investigated, and the quantum yields of 1O2 production (FD) and the rate constants of total quenching (kt) of 1O2 determined. Studied compounds do not produce 1O2 under UV-A irradiation and are very efficient 1O2 quenchers. The chemical reactions between 1O2 and dihydropterin derivatives were investigated and corresponding rate constants (kr) were found to be particularly high. The oxidized pterin derivatives, biopterin (BPT), neopterin (NPT), 6-formylpterin (FPT) and folic acid (FA), were identified and quantified during the reaction of 1O2 with DHBPT, DHNPT, FDHPT and DHFA, respectively. Besides the oxidation of the dihydropyrazine ring to yield the corresponding oxidized pterins, a second oxidation pathway, leading to the fragmentation of the dihydropterin and the formation of non-pterinic products, was identified. Mechanisms and biological implications are discussed.