Prediction and evaluation of the piperonylidene analogue of PBN by DFT calculations & NBT reduction mediated spectral assay

Two linear spin traps, α-piperonyl-N-tert-butylnitrone (PiBN) and its phosphoryl analogue N-(α-piperonylidene)-1-diethoxyphosphoryl-1- methylethylamine N-oxide (PiPN), have been first synthesized and structurally characterized. To improve the limitation in evaluating the kinetics of O ₂^-.-spin trapping in the aqueous solution, a nitroblue tetrazolium (NBT)-mediated spectral assay has been first fulfilled and examined in this work. On the other hand, to simplify the theoretical prediction on the kinetics, a density functional theory (DFT) LUMO calculation at the B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) level has been comparatively performed. All the results, when combined with calculating their optimized spin adducts, reveal that an introduction of the phosphoryl group not only can significantly stabilize its superoxide spin adducts, but increases the rate constant for the O₂^-.-spin trapping as well.