Reactivity of Conjugated and Unconjugated Pterins with Singlet Oxygen (O2(1Äg)): Physical Quenching and Chemical Reaction

FRANCO M. CABRERIZO; M. LAURA DÁNTOLA; GABRIELA PETROSELLI; ALBERTO L. CAPPARELLI; ANDRÉS H. THOMAS; ANDRÉ M. BRAUN; CAROLINA LORENTE; ESTHER OLIVEROS

PHOTOCHEMISTRY AND PHOTOBIOLOGY

Blackwell Publishing

Año: 2006

0031-8655

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. We have investigated the reactivity of conjugated pterins (folic acid (FA), 10-methylfolic acid (MFA), pteroic acid (PA)) and unconjugated pterins (pterin (PT), 6-hydroxymethylpterin (HPT), 6,7-dimethylpterin (DPT), rhamnopterin (RPT)) with singlet oxygen (1O2) in alkaline aqueous solutions, and compared the efficiencies of chemical reaction and physical quenching. The chemical reactions between 1O2, produced by photosensitization, and pterin derivatives were followed by UV-visible spectrophotometry and high-performance liquid chromatography, and corresponding rate constants (kr) were evaluted. Whenever possible, products were identified and quantified. Rate constants of 1O2 physical quenching by the pterin derivatives investigated were obtained from steady-state 1O2 luminescence measurements. Results show that the behavior of conjugated pterin differ from that of unconjugated derivatives, and the mechanisms of 1O2 physical quenching by these compounds and of their chemical reaction with 1O2 are discussed in relation with their structural features.