Photodegradation of hydroxylated N-heteroaromatic derivatives in natural-like aquatic environments

In the present review, the results published by our group and others related with the study of the kinetic behavior and, in some cases, the mechanism of the dye-promoted photooxygenation of several hydroxypyridines, hydroxyquinolines and hydroxypyrimidines-some of them with the basic molecular structures of known pesticides, and of a few non-hydroxylated model compounds, are compiled and discussed. The main aim was to examine the experimental conditions that maximize the photodegradation efficiencies of all these compounds, under dye-sensitized photooxidation conditions similar to those frequently found in nature, with a natural dye sensitizer such as riboflavin (vitamin B2), a pigment habitually present in natural waters. The usual mechanism of action of this compound is rather complex, in many cases with the concurrent involvement of the oxidative species singlet molecular oxygen (O2(1Δg)) and superoxide radical anion. In order to simplify the study of the processes, the results found using the synthetic dye Rose Bengal (RB), a sensitizer that generates O2(1Δg) with high efficiency, are also discussed. RB and similar O2(1Δg)-generators could be used for the efficient non-natural photodegradation of related pesticides in aqueous solutions under controlled conditions.