614 ABSORPTION SPECTRA OF PIGMENTS IN VITRO CHAP. 21 



curves in this figure were obtained by chromatographic separation of a 

 partially allomerized solution; a curve identical with curve h is obtained 

 by leaving a methanolic solution of chlorophyll a stand in air at 80°C. for 

 two days, or by adding to it 2-3 equivalents of iodine, or by adding traces 

 (10"^ ml.) of LaCls or CaCls. Standing in air, or addition of traces of 

 iodine, has no effect on the spectrum of chlorophyll a in ether or carbon 

 tetrachloride, except for slow general bleaching. If some methanol is added 

 to the nonpolar solvent, allomerization proceeds more slowly, but ends 

 with being as complete as in pure methanol; transfer of allomerized pro- 

 duct into pure ether or carbon tetrachloride does not reverse the change. 



In cresol, allomerization also seems to occur, but is complicated by other 

 changes, probably due to the acid nature of this solvent. 



Livingston and co-workers also have measured the absorption spectrum 

 of the yellow and brown unstable intermediates in the reactions of chloro- 

 phyll (in methanol) with FeCls (Vol. I, page 464) and with alkali (see 

 "phase test," Vol. I, page 459). The results will be described in chapter 37, 

 in the section dealing with new observations on the chemistry of chloro- 

 phyll. 



2. Absorption Spectra of Chlorophylls c and cl, Bacteriochlorophyll and 



Protochlorophyll 



The absorption spectrum of "chlorophyll c," also called chlorofucin (cf. 

 Vol. I, page 406), is characterized, according to the earlier authors (e. g., 

 Tswett), by a band in the region of 630 m/x. Strain and Manning (1942) 

 determined the extinction curve of this compound, first by subtraction of 

 the extinction curve of pure chlorophyll a from that of the chlorophyll ex- 

 tract from brown algae, and later by direct spectrophotometry of isolated 

 chlorophyll c. Figures 21. 5A and B show that the results of the two meth- 

 ods are in approximate agreement. Two "chlorofucin" bands are situated 

 in the orange and red — with peaks at 575.5 and 627 m/i, respectively, in 

 methanol, and at 581 and 631 m/x, respectively, in 80% acetone. Figure 

 21. 5C also shows a band in the blue (at 446 m^u) almost ten times stronger. 

 The ratio between the intensities of the bands in blue and red is thus much 

 larger than in chlorophyll b (where it is about 3), not to speak of chlorophyll 

 a (where the two bands are approximately equal in intensity, cf. Tables 

 21. IB and 21.VIII), but the general pattern of the spectrum is similar. 



Wa.ssink and Kersten (1946) and Tanada (1951) gave similar absorp- 

 tion curves for a "chlorophyll c" fraction from chromatographic frac- 

 tionation of the pigments of diatoms. The three absorption peaks ap- 

 pear, in methanol, at about 450, 590 and 635 m/u, with the first band about 

 ten times more intense than the other two (cf. p. 623). 



