Spin-trapping of free radicals by PBN-type β-phosphorylated nitrones in the presence of SDS micelles†

Abstract

Three PBN-type β-phosphorylated nitrones, PPN 1, 4-PyOPN 2, and 4-ClPPN 3, have been used to trap two carbon centred free radicals, CH₃˙ and CO₂^˙–, in a water–SDS biphasic system. The location of the traps and their adducts has been found by EPR spectroscopy. 4-PyOPN is found to remain in water, while 4-ClPPN is preferentially sequestered into the micellar structure, and PPN partitioned between the two phases. With the three nitrones, the CO₂^˙– spin adduct always remains in the bulk aqueous phase. In contrast, the three CH₃˙ spin adducts seem to be present in both phases. However, 4-PyOPN-CH₃ is essentially located in water, and 4-ClPPN–CH₃ in the micelles, while PPN–CH₃ is clearly shown to partition between the aqueous environment and the micellar interior. For all these spin adducts, the phosporus hyperfine splitting constant, a_P, is found to be a good indicator of aminoxyl behaviour in the presence of micelles. For the various sodium dodecyl sulfate concentrations, the PPN–CH₃ affinity for the micellar phase was evaluated from the average a_P value.