646 



VI. CAROTENOIDS AND RELATED COMPOUNDS 



apparent within 5 seconds. However, no inflection of the as peak was 

 observed over an interval of one hour when iodine catalysis was employed 

 in the dark. Moreover, the solvent is also of importance in determining 

 this effect. Whereas benzene, petroleum ether, and hexane all seemed to 

 allow the as-peak alteration to occur with equal effectiveness, lycopene, 

 when dissolved in carbon disulfide, '*^^ gave practically no response when re- 

 fluxed or catalyzed with iodine in the light. 



The isomers which adsorb below the a\\-t7-ans form on the chromato- 

 graphic column are mainly responsible for the ds-peak effect. ^^' In fact, 

 55 to 95% of the total effect has been demonstrated to be the result of one 



330 370 



WAVE LENGTH IN MJJ. 



Fig. 26. Molecular extinction curves of some members of the stereo- 

 isomeric lycopene set in the cts-peak region in hexane. Curve 

 marked I2 indicates the equilibrium mixture obtained upon iodine 

 catalysis at room temperature in light. ''^^ 



or two isomers (Table 32), namely neo A and neo B. In the poly -as forms 

 such as prolycopene and pro-7-carotene, the cis peak is negligible. The 

 molecular extinction coefficients at the as-peak wave lengths of the known 

 isomers are included in Table 33. The comparison of adsorption curves in 

 the as-peak region of an equilibrium mixture of lycopene isomers and of 

 the individual components is given in Figure 26. 



