Carotenoids circular-dichroism spectra

The determination of the absolute configuration of a carotenoid is only possible by circular dichroism (CD) measurement. The spectrum interpretation can only be done by comparison with reference or model compounds with known chiralities. The sample requirement is as low as 5 to 50 pg, but CD facilities are not so commonly available. Buchecker and Noack reported experimental aspects and discussion of the relationships of carotenoid structures and CD spectra. 

Circular Dichroism. Several papersreport the use of c.d. correlations in establishing the absolute configurations of carotenoids. One report sounds a cautionary note since the signs of all maxima in the c.d. spectrum of 15-cw-(3S,3 5)-astaxanthin are opposite to those of the all-trani-isomer. 

Optical Rotatory Dispersion and Circular Dichroism. O.r.d. data for several carotenoids have been tabulated.C.d. data have been recorded for astaxanthin (27 and 3S), /8,jS-carotene-2,3r3 -triol (6) and jS,/S-carotene-2,3,2, 3 -tetrol (7), decaprenoxanthin (37), the synthetic 2,2-dimethyl-e,e-carotenes (60) and (61)/ and the novel monocyclic C50 carotenoid (12). In the last case only very rough agreement was obtained between the observed spectrum and that calculated on the basis of the additivity hypothesis. ... 

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