ELECTROCHEMICAL AND OPTICAL STUDY OF CAROTENOIDS IN TX100 MICELLES : ELECTRON TRANSFER AND A LARGE BLUE SHIFT

The first oxidation waves of 8‘-apo-β-caroten-8‘-al (I) and 8‘-apo-β-caroten-8‘-nitrile (II) in TX100 micelles are clearly observed in their cyclic voltammograms (CVs). The CV of β-carotene (III) in TX100 micelles shows that III is not oxidized. It is proposed that the hydrophobic barrier of the micelle is an important reason for the failure to oxidize III, which is totally located in the hydrophobic center of the micelle. The oxidation of I and II demonstrates that electrons can be transferred through the terminal groups over a distance of ca. 22 A. An unusually large blue band shift (100 nm, relative to that in CH2Cl2) is observed in the optical absorption spectrum of 7‘-apo-7‘,7‘-dicyano-β-carotene (IV) in TX100 micelles. This phenomenon is not observed in the absorption spectra of other studied carotenoids. A change in the ground-state electronic structure of IV, due to the influence of water near the terminal dicyanomethylidene group, is proposed to be the major reason for this large band shift.