Unraveling the degradation mechanism of purine nucleotides photosensitized by pterins: the role of charge-transfer steps

Abstract

Photosensitized reactions contribute to the generation of skin cancer and are used in many applications. The photosensitizers may act through different mechanisms. It is currently accepted that if the photosensitizer generates singlet molecular oxygen (1O2) upon irradiation, the target molecule is able to be oxidized by this ROS and the reaction needs dissolved O2 to take place, the reaction is named a 1O2 -mediated oxidation (type II mechanism). However, this assumption is not always precise. As an example of this type of case, we present here a study on the degradation of 2´-deoxyguanosine 5´-monophosphate (dGMP) photosensitized by pterin. We propose a general mechanism to explain by the degradation of biological targets, such as nucleotides, photosensitized by pterins, naturally occurring 1O2 photosensitizers, takes place through an electron-transfer initiated process (type I mechanism), being almost negligible the contribution of the 1O2 -mediated oxidation.