Electron-transfer processes induced by the triplet state of pterins in aqueous solutions.
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.
Dántola
M Laura
ML
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.
Vignoni
Mariana
M
González
Constanza
C
Lorente
Carolina
C
Vicendo
Patricia
P
Oliveros
Esther
E
Thomas
Andrés H
AH
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
D017319:Photosensitizing Agents; D011622:Pterins; D012996:Solutions; D004492:Edetic Acid; D006861:Hydrogen Peroxide