61G ABSORPTION SPECTRA OF PIGMENTS 7.V VITRO CHAP. 21 



The absorption spectrum of the '' chlorophyll d" of red algae also was 

 determined by Manning and Strain (1943). Since this investigation was j 

 only briefly mentioned in Vokime I, a few words may be said here about 

 this newly discovered pigment. Its presence is revealed by a bulge on the 

 red side of the chlorophyll a band, observed in the spectra of methanol 

 extracts from red algae. In pure chlorophyll a solution in methanol, the 

 ratio of extinction coefficients at 665 and 700 m^u is 90; in extracts from 

 twenty red algae, this ratio was between 15 and 65. Short extraction leads 

 to products with even lower I'atios ; r. g. , t wo minutes extraction of Gigarlina 

 agardhii gave a product Math a ratio of only 10:1. Apparently, chlorophyll d 

 is much more easily extracted by methanol than chlorophyll a. Chromato- 

 graphic purification can be used for the preparation of pin-e chlorophyll d. 

 Figure 21.51) shows the spectrum of this pigment in methanol. In ethyl 

 ether, the band maxima of chlorophyll d lie at 686 and 445 myu, and below 

 395 niju. 



In spectrum as well as in solubility and other chemical properties, 

 chlorophyll d resembles chlorophyll a more than chlorophyll h. Careful 

 search for chlorophjdls h and c in the chromatograms of pigments from red 

 algae gave negative results (the upper limit foi- tlie content of chlorophyll h 

 is 0.3% of that of chlorophyll a). 



The isornerization of chlorophyll d was mentioned in chapter 16 (Vol. 

 I). It occurs in the methanolic solution upon standing in the dark, in the 

 presence or absence of air, and leads to three new pigments, which seem 

 to be interconvertible. They were designated chlorophyll d', isochloro- 

 phyll d and isochlorophyll d'. The spectra of the components d and d', 

 respectively, are very similar, and the same is true of those of the isomers 

 iso-d and iso-c?'. The latter two spectra are almost identical with those of 

 the chlorophylls a and a' (cf. fig. 21. 5E) ; but the maximum of chlorophyll 

 iso-d and iso-d' lies about 5 mfu. further toward the blue (cf. fig. 21.5 F). 

 The red band of chlorophyll d (and d') lies about 37 m^ further toward the 

 infrared than that of chlorophylls a and a' (cf. fig. 21.5F). 



Isochlorophylls d and d' are not found in fresh extracts from algae. 

 The conversion d -^ iso-d appears to be slower than the conversions d-^ d' 

 and iso-d -^ iso-d'. 



Four interconvertible pheophytins with diffei'ent spectra were pro- 

 duced by the action of acids on the four d-pigments; but successive treat- 

 ment with alkali and acid led to spectroscopically identical products for 

 all four d-pigments. These products are distinct from the compounds ob- 

 tained by a similar treatment of either of the two a-pigments. Table 

 21. Ill illustrates the relationships between the six pigments a, a', d, d', 

 iso-d and iso-d' and their transformation products. 



The main absorption band of the bacteriocMorophyll of purple bacteria 



