Authentic versus alternative mechanisms in spin trapping. Formation of azide spin-adducts in biphasic and non-aqueous systems by the oxidation of azide anion with a variety of hydrazyl radicals

Abstract

The formation of azide spin-adducts of a number of spin-traps, including PBN, DMPO, DEPMPO and TBNB, in biphasic and organic media has been studied by EPR spectroscopy. A series of hydrazyl radicals has been employed to oxidise the azide anion to the corresponding short-lived azido radical, which is subsequently trapped. The approach has typically involved the presence of the ether 18-crown-6 in order to facilitate the transport of the azide anion from water into the organic media, with further experiments in non-aqueous systems. The results can largely be rationalised in terms of a “conventional” spin-trapping mechanism, with an efficiency that depends on the relevant redox potentials, which are themselves solvent dependent; however, conditions that favour direct oxidation of the trap have also been identified. It is also established that the azide spin-adducts of some nitrones can be transformed, under certain conditions, into secondary spin-adducts by nucleophilic substitution reaction of the first-formed nitroxides.