Absorption spectrophotometric studies indicated that in chloroform β-carotene reacted with NO2 with a stoichiometry of 1:2. To understand the reaction mechanism, free radical intermediates produced during their reaction were trapped by spin traps 2-methyl-2-nitroso propane (MNP) and 4-pyridyl-1-oxide-N-1-butyl nitrone (POBN). The resulting stable spin adducts were detected by electron spin resonance (ESR) spectroscopy. NO2 alone did not interact with spin traps, but introduction of β-carotene-generated ESR signals with different nitrogen and hydrogen hyperfine coupling constants (A N and A H) characteristsic of the trapped radical. Two possible pathways exist for the reaction of NO2 with β-carotene, viz., electron transfer and addition to the polyene chain. Our ESR results supported an addition mechanism, where formation of carbon-centered [NO2 · · · β-carotene] free radical adduct was observed.
Research on Chemical Intermediates – Springer Journals
Published: Oct 17, 2004
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