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Kinetics and Mechanism of the Vitamin B 2 ‐sensitized Photooxidation of Isoproterenol ¶
Author(s) -
Massad Walter A.,
Bertolotti Sonia,
Garcia Norman A.
Publication year - 2004
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2004.tb00030.x
Subject(s) - chemistry , photochemistry , photodegradation , singlet oxygen , quenching (fluorescence) , kinetics , reaction rate constant , superoxide , oxygen , electron transfer , triplet state , singlet state , excited state , fluorescence , molecule , catalysis , organic chemistry , physics , photocatalysis , quantum mechanics , enzyme , nuclear physics
The sensitized photooxidation promoted by daylight‐absorbing compounds appears as a plausible course to produce the photodegradation of catecholamines. We report the kinetics and mechanism of vitamin B 2 (reiboflavin [Rf])‐sensitized photooxidation of isoproterenol (Isoproterenol (Iso), a synthetic sympathomimetic drug structurally related to epinephrine, using water as a solvent. A week dark complex Rf‐Iso is formed, only detectable at relatively high Iso concentrations (>10 m M ), with a mean value of 13 ± 3 M −1 for the apparent association constant. Under aerobic sensitizing conditions ( Rf ∼ 0.02 m M and Iso ∼ 0.5 m M ) two oxidative mechanisms operate, mediated by singlet molecular oxygen (O 2 ( Δ g )) and superoxide radical anion (O 2 •− ). Our analysis shows that the main reaction pathway is an electron transfer‐mediated quaenching of Rf excited triplet state ( 3 Rf*) by Iso. It produces the species Iso •+ and Rf •− . The latter, in a subsequent reaction path, generates O 2 •− , which is mainly responsible for Iso Photooxygenation. In a less‐important process, energy transfer of the 3 Rf* to dissolved oxygen generates O 2 ( Δ g ). The kinetic balance between chemical and physical quenching of O 2 ( 1 Δ g ) by Iso indicates that the process is largely dominated by the physical, not chemical, interaction. The results, which can be extrapolated to an in vivo condition, show the susceptibility of Iso to undergo visible light‐induced photodegradation in the presence of dye sensitizers present in the environment.