Visible-light-promoted degradation of the antioxidants propyl gallate and t-butylhydroquinone: Mechanistic aspects

The kinetic and mechanistic aspects of the visible-light-mediated photodegradation of the phenolic antioxidants (PA), propyl gallate (PG), and t-butylhydroquinone (TBHQ), employing riboflavin (Rf) as photosensitizer, have been studied by time-resolved and stationary techniques. The photosensitizer R...

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Bibliographic Details
Published in:Redox report : communications in free radical research 2012-05, Vol.17 (3), p.131-138
Main Authors: Criado, Susana, Allevi, Carolina, García, Norman A.
Format: Article
Language:English
Subjects:
Animals
Antioxidants
Antioxidants - chemistry
Fluoroimmunoassay
Hydrogen Peroxide - chemistry
Hydroquinones - chemistry
Hydroxyl Radical - chemistry
Light
Luminescent Measurements - methods
Photolysis
Photooxidation
Propyl gallate
Propyl Gallate - chemistry
Reactive Oxygen Species
Riboflavin
Rose Bengal - chemistry
Singlet Oxygen - chemistry
t-buthylhydroquinone
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Summary:The kinetic and mechanistic aspects of the visible-light-mediated photodegradation of the phenolic antioxidants (PA), propyl gallate (PG), and t-butylhydroquinone (TBHQ), employing riboflavin (Rf) as photosensitizer, have been studied by time-resolved and stationary techniques. The photosensitizer Rose Bengal (RB) was used for auxiliary experiments. Results show the occurrence of chemical transformations on PA with the participation of electronically excited states of Rf and different reactive oxygen species (ROS) generated from these states. With 0.02 mM Rf and 1.0 mM PA, the electronically excited triplet state of Rf is quenched by PA, in a competitive manner with the dissolved oxygen. As a consequence, a cascade of photoprocesses produces singlet oxygen (O 2 ( 1 Δ g )) and H 2 O 2 in the case of PG and, O 2 ( 1 Δ g ), H 2 O 2 and HO * in the case of TBHQ. The participation of these species is supported by experiments of oxygen consumption carried out in the presence of specific ROS scavengers. TBHQ has a relatively high capacity for O 2 ( 1 Δ g ) physical deactivation and a low photodegradation efficiency by the oxidative species. Comparatively, it can be asserted that TBHQ has a higher antioxidant capacity than PG.
ISSN:1351-0002
1743-2928
1743-2928
DOI:10.1179/12Z.00000000018