Electron transfer from all-trans β-carotene to the t-butyl peroxyl radical at low oxygen pressure (an EPR spectroscopy and computational study)

It has been documented that less strongly oxidising radicals, including alkylperoxyl radicals, react with carotenoids via hydrogen atom transfer, thereby generating the neutral carotene radical. In this work, we have studied the reaction between the weakly oxidising t-butyl peroxyl radical (TBHP) and β-carotene in dichloromethane under low oxygen pressure. Despite the rather low value of the reduction potential of TBHP, we have succeeded in the formation of the cation radical of β-carotene (β-carotene+). Based on EPR and NIR-IR spectroscopy, the reaction mechanism for this reaction has been assigned to an electron transfer mechanism. This relatively rare mechanism for the reaction between less strongly oxidising species, such as the TBHP radical and carotenoids has been explained on the basis of DFT and DFT–PCM calculations.