Methyl anthranilate as generator and quencher of reactive oxygen species: A photochemical study

Methyl anthranilate (MA) is a naturally occurring aromatizer and flavorant agent frequently employed in food industry and in personal care products. Due to the property of MA of being a UV-A radiation-absorber it is incorporated to topical sunscreen formulations. Within the framework of the wide variety of practical uses and applications, the photodegradation of MA becomes a topic of interest from health to an economic point of view. In this context, kinetics and mechanistic aspects of its photo-oxidation has been studied, in order to know the degradation pathways of MA under natural-like photoirradiation. The assays were performed in the absence and in the presence of riboflavin (Rf, vitamin B-2) acting the later as a native photosensitizer. The results showed that MA is capable to generate singlet molecular oxygen (O-2((1)Delta(g))) upon direct UV-A irradiation, with a quantum yield value of 0.13 +/- 0.02. The anthranilate also quenches the oxidative species with an overall rate constant value k(t) =2.1 +/- 0.2 x 10(7) M-1 s(-1) while the reactive interaction between MA and O-2((1)Delta(g)) showed a rate constant value in the range of 5.9-6.8 x 10(6) M-1 s(-1). The k(r)/k(t) ratio, lower than 0.35 indicates that only one third of the O-2((1)Delta(g))-quenching events effectively lead to oxidation of the scavenger, being this an acceptable property for a sunscreen component. Regarding the Rf-photosensitized visible-light irradiation of MA-Rf mixtures, the anthranilate quenches the electronically excited singlet and triplet states of the vitamin. As a result the oxidative species O-2(center dot-) and H2O2, are generated, being the later effectively deactivated by MA. At first, the described results would show MA as a candidate for UV-A and visible-light mediated degradation. Nevertheless, at the same time MA acts as a moderate physical scavenger of photogenerated oxidative species in a sort of self-protector against photoinduced degradation and protector of oxidizable surrounding compounds. (C) 2013 Elsevier B.V. All rights reserved.