Spin trapping of superoxide by diester-nitrones

The nitrone N-[(1-oxidopyridin-1-ium-4-yl)-methylidene]-1,1-bis(ethoxycarbonyl) ethylamine N- oxide (DEEPyON) was synthesized and used as a spin trapping agent. The kinetic aspects of the superoxide detection by this new spin trap and by two other diester-nitrones, i.e. 2,2-diethoxycarbonyl-3,4-dihydro-2H-pyrrole-1-oxide (DEPO) and N-benzylidene-1,1-bis(ethoxycarbonyl)ethylamine N-oxide (DEEPN), were examined by determining the rate constants for the trapping reaction and for the spin adduct decay at pH 7.2. Comparing the results obtained to those given by analogous monoester-nitrones showed that both the spin trapping and the adduct decay reactions were faster in the presence of a second ester group in the cyclic nitrone series, while the superoxide trapping capacities of linear diester-nitrones were found to be dramatically weak. It follows from this study that DEPO and 2-ethoxycarbonyl-2-methyl-3,4-dihydro-2H-pyrrole-1-oxide (EMPO) are superior when it comes to superoxide detection. Below 0.005 mol dm(-3), DEPO is to date the only nitrone capable of clearly detecting superoxide, while EMPO should be preferred at higher spin trap concentration.