Spectroscopic studies of neutral and chemically oxidized species of (3-carotene, lycopene and norbixin in CH2C12 Fluorescence from intermediate compounds

Abstract

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Radical cations, dications and oxidized interm ediate species of three carotenoids, namely, P-carotene, lycopene and norbixin, w ere generated in CH2C12 solutions via chemical oxidation using anhydrous FeCl3. UV-vis, fluorescence and fluorescence-excitation spectroscopic studies w ere perform ed to understand and com pare th e nature of interm ediate species generated during the chemical oxidation process and subsequent degradation. The intense em ission observed at 550 nm can be assigned to the S2->S0 ( l l Bu-> l1Ag) transition of the carotenoid molecules. The 350 nm excitation during the oxidation process for P-carotene, lycopene and norbixin exhibit intense fluorescence peaks at 492 nm , 493 nm and 500 nm , respectively. These peaks are assigned to interm ediate peroxy/epoxy com pounds of the three m olecules th at are form ed w ith molecular oxygen prior to the form ation of oxidized short-chain stable compounds.