title: Electron-transfer processes induced by the triplet state of pterins in aqueous solutions.
abstract: 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/Vis spectrophotometry, HPLC, and an enzymatic method for H(2)O(2) determination. The formation of the superoxide anion (O(2)(*-)) 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 O(2) to yield O(2)(*-), 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 H(2)Pt. The effects of EDTA and dissolved O(2) concentrations on the efficiencies of the different competing pathways were analyzed.
authors.affiliation: Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET, 1900 La Plata, Argentina.
authors.forename: M Laura
authors.initials: ML
authors.lastname: Dántola
authors.forename: Mariana
authors.initials: M
authors.lastname: Vignoni
authors.forename: Constanza
authors.initials: C
authors.lastname: González
authors.forename: Carolina
authors.initials: C
authors.lastname: Lorente
authors.forename: Patricia
authors.initials: P
authors.lastname: Vicendo
authors.forename: Esther
authors.initials: E
authors.lastname: Oliveros
authors.forename: Andrés H
authors.initials: AH
authors.lastname: Thomas
mesh_terms: D002851:Chromatography, High Pressure Liquid; D004492:Edetic Acid / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport / Q000528:radiation effects; D006861:Hydrogen Peroxide / Q000737:chemistry*; D066298:In Vitro Techniques; D010084:Oxidation-Reduction / Q000528:radiation effects; D055668:Photochemical Processes; D017319:Photosensitizing Agents / Q000737:chemistry*; D011622:Pterins / Q000737:chemistry*; D012996:Solutions; D014466:Ultraviolet Rays
chemical_list: D017319:Photosensitizing Agents; D011622:Pterins; D012996:Solutions; D004492:Edetic Acid; D006861:Hydrogen Peroxide