INIFTA   05425
INSTITUTO DE INVESTIGACIONES FISICO-QUIMICAS TEORICAS Y APLICADAS
Unidad Ejecutora - UE
artículos
Título:
Photochemistry of dihydrobiopterin in aqueous solution
Revista:
Organic and Biomolecular Chemistry
Editorial:
RSC
Referencias:
Año: 2010 vol. 8 p. 800 - 810
Resumen:
Dihydrobiopterin (H2Bip) and its oxidized
analogue, biopterin (Bip), accumulate in the skin of patients suffering
from vitiligo, a chronic depigmentation disorder in which the
protection against UV radiation fails. The photochemistry of H2Bip
was studied in neutral aqueous solutions upon UV-A irradiation (320400
nm) at room temperature. The photochemical reactions were followed by
UV/vis spectrophotometry, HPLC and enzymatic methods for hydrogen
peroxide (H2O2)
determination. Photoproducts were analyzed by means of electrospray
ionization mass spectrometry. Under anaerobic conditions, excitation of
H2Bip leads to the formation of at least two
isomeric dimers with molecular masses equal to exactly twice the
molecular mass of the reactant. This reaction takes place from the
singlet excited state of the reactant. To the best of our knowledge,
this is the first time that the photodimerization of a dihydropterin is
reported. In the presence of air, the dimers are again the main
photoproducts at the beginning of the reaction, but a small proportion
of the reactant is converted into Bip. As the reaction proceeds and
enough Bip accumulates in the solution, a photosensitized process
starts, where Bip photoinduces the oxidation of H2Bip to Bip, and H2O2 is formed. As a consequence, the rates of H2Bip
consumption and Bip formation increase as a function of irradiation
time, resulting in an autocatalytic photochemical process. In this
process, Bip in its triplet excited state reacts with the ground state
of H2Bip. The mechanisms involved are analyzed and the biological implications of the results are discussed.