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

Abstract

The radical cation PBN˙⁺2 of the spin trap α-phenyl-N-tert-butylnitrone (PBN, 1) was observed directly {λ_max(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.