Electron transfer processes induced by the triplet state of pterins in aqueous solutions

M. LAURA DÁNTOLA; MARIANA VIGNONI; CONSTANZA GONZALEZ; CAROLINA LORENTE; PATRICIA VICENDO; ESTHER OLIVEROS; ANDRÉS H. THOMAS

FREE RADICAL BIOLOGY AND MEDICINE

ELSEVIER SCIENCE INC

Año: 2010 vol. 49 p. 1014 - 1022

0891-5849

Pterins (Pt) are heterocyclic compounds widespread in living systems. They participate in relevant biological processes, such as metabolic redox reactions, and can photoinduce the oxidation of biomolecules through electron-transfer mechanisms. We have investigated the electron-transfer pathways initiated by excited states of pterin (Ptr) and 6-methylpterin (Mep), selected as model compounds. The experiments were carried out in aqueous solutions under continuous UV-A irradiation, in the presence and in the absence of ethylenediaminetetraacetic acid (EDTA), used as an electron donor. The reactions were followed by UV/Visspectrophotometry, HPLC, and an enzymatic method for H2O2 determination. The formation of the superoxide anion (O2•−) was investigated by electron paramagnetic resonance–spin trapping. The triplet excited states of Ptr and Mep are efficient electron acceptors, able to oxidize a Pt molecule in its ground state.The resulting radical anion (Pt•−) reacts with dissolved O2 to yield O2•−, regenerating the pterin. In the presence of EDTA, this reaction competes efficiently with the anaerobic reaction between Pt•− and EDTA•+, yielding the corresponding stable dihydroderivatives H2Pt. The effects of EDTA and dissolved O2 concentrations on the efficiencies of the different competing pathways were analyzed.