Direct detection of the cation radical of the spin trap α-phenyl-N-tert-butylnitrone

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Abstract
The radical cation PBN˙+2 of the spin trap α-phenyl-N-tert-butylnitrone (PBN, 1) was observed directly {λmax(H2O)/nm 410 [ε/dm3 mol–1 cm–1(5 ± 1)× 103]} and characterised by pulse radiolysis and laser flash photolysis absorption measurements in solvents of different polarity (water, CH3CN, BuCl) as well as by low-temperature EPR. It was generated by direct two-photon ionisation of PBN, by electron-transfer from PBN to solvent cation radicals or to photoexcited triplet chloranil, and by reaction of PBN with the oxidising anion radical SO4˙–. The γ-irradiation of PBN in alkyl halide glasses at 77 K yielded green-coloured samples containing the stabilised radical cation PBN˙+, whose EPR spectrum indicates the presence of aminoxyl-type radicals. PBN˙+ reacts with a variety of nucleophiles to yield the corresponding stable aminoxyl radicals. Based on spectroscopic, kinetic and chemical evidence it is concluded that PBN˙+ is an aminoxyl substituted phenylcarbenium ion.