INVESTIGADORES
MASSAD Walter Alfredo
artículos
Título:
Dye-sensitized photodegradation of the fungicide carbendazim and related benzimidazoles
Autor/es:
JUAN P. ESCALADA; ADRIANA PAJARES; JOSÉ GIANOTTI; WALTER A. MASSAD; SONIA BERTOLOTTI; FRANCISCO AMAT-GUERRI; NORMAN A. GARCÍA
Revista:
CHEMOSPHERE
Referencias:
Año: 2006 vol. 65 p. 237 - 244
ISSN:
0045-6535
Resumen:
The
present work studies the visible-light-promoted photodegradation of the
colorless fungicide carbendazim (methyl 2-benzimidazolecarbamate) and several
2-substituted benzimidazoles (SBZs), in water or watermethanol solution, in
the presence of air and, as a photosensitizer, the synthetic xanthene dye Rose
Bengal (RB) or the natural pigment riboflavin (Rf). The results indicate that
the degradation of each particular SBZ depends on its chemical structure and on
the sensitizer employed. In the presence of RB, the degradation always operates
via a singlet molecular oxygen (O2(1Dg))-mediated
mechanism, through a highly efficient process, as deduced from the comparison
of the rate constants for physical and chemical quenching of O2(1Dg).
In the presence of Rf, the visible-light irradiation of any of the studied SBZs
produces a series of competitive processes that depend on the relative
concentrations of Rf and SBZ. These processes include the quenching of excited
singlet and triplet Rf states by the SBZ and the generation of both O2(1Dg)
and superoxide radical anion (O2·-) ,
the latter generated by electron transfer from excited Rf species to the
dissolved oxygen. The overall result is the photodegradation of the SBZ and the
photoprotection of the sensitizer.