Singlet Oxygen (O2(1Dg)) Quenching by Dihydropterins

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

JOURNAL OF PHYSICAL CHEMISTRY A

American Chemical Society

Año: 2007 vol. 111 p. 4280 - 4288

1089-5639

6-Substituted 7,8-dihydropterins are heterocyclic compounds that occur in a wide range of living systems and participate in relevant biological functions. In air-equilibrated aqueous solutions these compounds react with dissolved O2 (autooxidation). The rates of these reactions, as well as, the products formed strongly depend on the chemical structure of the substituents. 6-Methyl-7,8-dihydropterin and 6,7-dimethyl-7,8-dihydropterin, that bear electron-donor groups as substituents, are the most reactive derivatives and undergo oxidation of the pterin moiety to yield the corresponding oxidized derivatives (6-methylpterin and 6,7-dimethylpterin, respectively). The oxidations of 7,8-dihydrobiopterin, 7,8-dihydroneopterin and 7,8-dihydrofolic acid are slower and yield 7,8-dihydroxanthopterin as the main product. 7,8-dihydroxanthopterin, 6-formyl-7,8-dihydropterin and sepiapterin are rather stable and their consumption in air-equilibrated solutions is negligible for several days. The pseudo-first order rate constants of the reactions between these compounds and O2 at 25o and 40o are reported. The biological implications of the results obtained are also discussed.