662 



ABSORPTION SPECTRA OF PIGMENTS IN VITRO 



CHAP. 21 



at 426, 450 and 476 mn (Table 21. IX). The curves given by them for 

 Hve diatoms, colloidal extracts and pigment solutions in organic solvents 

 indicate a considerably increased absorption, in vivo, in the region 500- 

 560 mju. 



Table 21. IX shows that the absorption bands of many bacterial carote- 

 noids are situated further toward the red than those of green plants and 

 algae — a relation that reminds one of that between chlorophyll and bac- 

 teriochlorophyll. 



Figures 21.31 and 32 show the extinction curves of three carotene iso- 

 mers and figures 21.33 and 21.34 those of luteol — the most common carote- 

 nol of green plants (c/. Vol. I, page 415). Figures 2 1.35 A and B repre- 

 sent the spectra of several carotenols of broAvn algae, diatoms and dino- 

 flagellates. 



300 

 260 

 220 

 180 

 140 

 100 

 60 



4510 A 



-o4780 

 4680 



>4920 



J I L 



J I L 



4 8 12 16 20 24 28 

 SPECTRAL REGION ISOLATED, m^ 



Fig. 21.37. Effect of width of spectral region isolated on the 

 specific absorption coefficient of /3-carotene at selected wave lengths 

 (after Zscheile, White, Beadle and Roach 1942). The changes in a 

 observed by Miller with single monochromator (•) were not found in 

 the work with a double monochromator (O). 



The absorption bands of the carotenoids are much broader than those of chloro- 

 phyll; they are therefore less sensitive to changes in the width of the slit, as illustrated 

 by figure 2i.37. 



2. Theoretical Considerations 



Carotenoids are 'polyene dyestuffs, i. e., their color is due to the chromo- 

 phoric properties of a straight chain of conjugated double bonds. Syn- 

 thetic polyenes, and the cyanine dyestuffs used in photographic sensitiza- 

 tion, are other examples of the same type. With increasing length of the 



