Pulse radiolytic oxidation of β-carotene with halogenated alkylperoxyl radicals in a quaternary microemulsion:: formation of retinol

Pulse radiolytically generated halogenated alkylperoxyl radicals, namely CCl3OO, CBr3OO., CHCL2OO., CHBr2OO., etc, have been employed for a study of the oxidation of beta -carotene in a quaternary microemulsion. All these halogenated alkylperoxyl radicals produce a radical cation (absorption maximum at 840 nm), either via the initial formation of an adduct (absorption maximum at 740 nm), or by direct reaction. There was a considerable blue shift of both absorption peaks in the present system as compared to those earlier reported in non-polar as well as in micellar media. An additional intense absorption peak at approximately 345 nm was noted at a longer time scale and was stable up to 5 ms. On irradiation with a large number of electron pulses, a stable product with an absorption maximum at 315 nm appeared. On excitation at 315 nm, this product gave a fluorescence spectrum with an emission maximum at 525 nm. The absorption and fluorescence spectra of the stable product compared with those of retinol; this was further confirmed by HPLC analysis. A suitable mechanism has been proposed. (C) 2000 Elsevier Science B.V. All rights reserved.