INVESTIGADORES
MASSAD Walter Alfredo
artículos
Título:
A kinetic study on the inhibitory Action of Sympathomimetic Drugs Towards Photogenerated Oxygen Active Species. The Case of Phenylephrine
Autor/es:
WALTER A. MASSAD; SONIA G. BERTOLOTTI; MARIO ROMERO; NORMAN A. GARCÍA
Revista:
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY
Referencias:
Año: 2005 vol. 80 p. 130 - 138
ISSN:
1011-1344
Resumen:
Kinetics
and mechanism of the aerobic Riboflavin (Rf, vitamin B2) sensitized
photodegradation of Phenylephrine (Phen), a phenolamine belonging to the
sympathomimetic drugs family, has been studied in water, employing continuous photolysis,
polarographic detection of oxygen uptake, steady-state and time-resolved
fluorescence spectroscopy, time-resolved IR-phosphorescence and laser flash
photolysis. Results indicate the formation of a weak dark complex Rf-Phen, with
an apparent association constant of 5.5 ±
0.5 M-1, only detectable at Phen concentrations much higher than
those employed in the photochemical experiments. Under irradiation, an intricate
mechanism of competitive reactions operates. Phen quenches excited singlet and triplet states
of Rf, with rate constants of 6.2 x 109 M-1s-1
and 4.7 x 109 M-1s-1, respectively. With the sympathomimetic drug in a concentration similar to that of dissolved
molecular oxygen in water, Phen and oxygen competitively quench triplet excited
Rf, generating superoxide radical anion and singlet molecular oxygen (O2(1Dg))
by processes initiated by electron- and energy-transfer mechanisms
respectively. As a global result, the
photodegradation of the vitamin, a known process taking place from its
excited triplet state, is retarded, whereas the phenolamine,
practically unreactive towards these oxidative species, behaves as a highly efficient physical deactivator of O2(1Dg).
The phenolamine structure in Phen appears as an excellent scavenger of
activated oxygen species, comparatively superior, in kinetic terms, to some
commercial phenolic antioxidants.