Electrochemical and optical study of carotenoids in TX100 micelles: Electron transfer and a large blue shift

The first oxidation waves of 8'-apo-beta-caroten-8'-al (I) and 8'-apo-beta- caroten-8'-nitrile (II) in TX100 micelles are clearly observed in their cyc lic voltammograms (CVs). The CV of beta-carotene (III) in TX100 micelles sh ows that II is not: oxidized. It is proposed that the hydrophobic barrier o f 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 term inal groups over a distance of ca. 22 Angstrom. An unusually large blue ban d shift (100 nm, relative to that in CH2Cl2) is observed in the optical abs orption spectrum of 7'-apo-7',7'-dicyarzo-beta-carotene (IV) in TX100 micel les. This phenomenon is not observed in the absorption spectra of other stu died carotenoids, A change in the ground-state electronic structure of IV, due to the influence of water near the terminal dicyanomethylidene group, i s proposed to be the major reason for this large band shift.