AN ENDOR STUDY OF CAROTENOID CATION RADICALS ON SILICA-ALUMINA SOLID SUPPORTS

The cation radicals of canthaxanthin, beta-carotene and 8'-apo-beta-ca roten-8'-al were chemically prepared on activated silica-alumina solid supports. An ENDOR study of these cation radicals revealed the hyperf ine coupling constants of the methyl protons and indicated a carotenoi d-dependent orientation of the cation radicals bound to the solid supp ort. The Lewis acidic sites of the solid support appear to be responsi ble for the chemical formation of the cation radicals and the Bronsted acidic sites are responsible for the stability of the cation radical produced on the support.