Circular Dichroic Spectra of Mono-cis Carotenoids.

Abstract
CD (circular dichroism) spectra of the cis-trans isomers present in the iodine catalyzed stereomutation mixtures of [Flavobacterium] zeaxanthin, [Prymnesium parvum] diatoxanthin (2) and alfalfa lutein (3) are reported. The mono-cis isomers exhibit opposite Cotton effects relative to the all-trans isomers. The intensity of the CD bands in the so-called cis-region is enhanced for mono-cis isomers, particularly those with near-to-central cis bonds. Chiral centra at C-3 and C-2 in all-trans-carotenoids containing .epsilon.-rings do not contribute significantly to their CD spectra. 19-Hydroxylation appears to influence the chiroptical properties.