Reactions of indolic nitrones and N-heteroaromatic bases under irradiation and chemical oxidation

Indolinonic and quinolinic aromatic nitroxides have been shown to efficiently inhibit free radical mediated oxidation reactions in biological systems. Since all antioxidants also possess pro-oxidant activity, possibly through a hydrogen abstraction process from suitable substrates, the relative hydrogen abstraction abilities of these compounds were evaluated also in relation to their structure. Therefore, different hydrogen donors were reacted with indolinic, indolinonic and quinolinic nitroxides and the rates of hydrogen abstraction were determined using UV-Vis spectroscopy. From the data obtained, a structure-activity relationship was found for indolinonic and indolinic nitroxides. In addition, hydrogen abstraction abilities of these compounds were much greater when compared to that of the aliphatic nitroxide TEMPO, although the antioxidant activities of these two classes of compounds are very similar.