Photosensibilisierte O2-Übertragung in Gegenwart oder mittels β-Carotin unter Ausschluß von Singulett-Sauerstoff

Abstract

Carotenoids and vitamin A may react as sensitizers, substrates, quenchers and scavengers in photo- and autooxidation processes. β-Carotene has been shown to act as sensitizer in type 2 photooxygenation of dienes and olefins generating singlet oxygen (¹O₂) in the Kautsky-Schenck mechanism via excited carotene-O₂ complexes. Strong quenching of ¹O₂ by β-carotene has been found especially occuring in solvents containing benzene as applied by Foote and Denny, but not in methanol or isopropanol, etc. ¹O₂-Quenching appears to be associated with oxygenation of β-carotene and is interpreted as catalytic action via complexing of ¹O₂ with β-carotene. The difference in behavior of the excited sensitizer-oxygen-complexes and of the quencher/acceptor-oxygen-complexes is explained by the different states of aggregation of the β-carotenes in various solvents. Association e.g. in alcohols appears favouring sensitization, whereas stronger solvation by benzene is favouring acceptor and associated catalytic or quenching activities. The problem of solvation of ¹O₂ needs further consideration.