INVESTIGADORES
CABRERIZO franco Martin
artículos
Título:
Photochemical behavior of folic acid in alkaline aqueous solutions and evolution of its photoproducts
Autor/es:
A.H. THOMAS; G. SUÁREZ; F.M. CABRERIZO; F.S. GARCÍA EINSCHLAG; R. MARTINO; C. BAIOCCHI; E. PRAMAURO; A.L. CAPPARELLI
Revista:
HELVETICA CHIMICA ACTA
Referencias:
Año: 2002 vol. 85 p. 2300 - 2315
ISSN:
0018-019X
Resumen:
Abstract
Photochemical and kinetic
studies of the reactivity of folic acid in alkaline aqueous solutions were
performed. The photolysis of the substrate was carried out at 350 nm at room
temperature in the pH range 10.0-11.0. UV-VIS spectrophotometry, thin layer
chromatography (TLC), both for analytical and preparative purposes, and high
performance liquid chromatography (HPLC, HPLC/MS) were applied to follow the
phototransformation of folate. This species undergoes, at least, two
independent photooxidation pathways, which are not observed when the acid form
of this substance is photolyzed at pH <7. The presence of dioxygen is
essential in these pathways. Evidences on the role of singlet oxygen are
reported. In one of these pathways folic acid undergoes cleavage, yielding
6-formylpterin and p-aminobenzoylglutamic
acid as photoproducts. The other pathway yields a new photoproduct (here named
as substance A) having a molecular
weight of 455. This new compound A
is photostable, can be isolated and stored in acidic or neutral solutions
aqueous solutions. However, this compound is rather unstable in alkaline media,
where it undergoes a thermal reaction, yielding a product of lower molecular
weight (427). The kinetic of this thermal reaction was analyzed using a stopped
flow equipment. A linear dependence of the first order rate constant with the OH- concentration is observed. The corresponding
bimolecular rate constant was determined (1.1 M-1s-1).
The quantum yields of substrates consumption and of photoproducts formation are
reported. The photochemical behavior of folate solutions reported in the
present communication departs from results in acid media, where
phototransformation proceeds through the cleavage of the acid form into 6-formylpterin
and p-aminobenzoylglutamic acid as
the first major photoproducts and no thermal reactions are observed