CHLOROPHYLLS tt AND h 



605 



10% of chlorophyll a. Its presence can easily be recognized by increased 

 light absorption at 614 mju. According to Biermacher (1939), the fluores- 

 cence spectrum of chlorophyll b is even more senstive to contamination with 

 chlorophyll a than the absorption spectmm (cf. chapter 23, page 744). 

 He recommended extraction with hexane (which dissolves chlorophyll a 

 much more easily than chlorophyll b) as a means of final purification of the 

 6-component . Extraction is repeated until the fluorescence spectrum of the 

 residue no longer shows the chlorophyll b band. 



Meyer (1939) asserted that the band at 535 ni/u, which is noticeable in most if not 

 all extinction curves of pure chlorophyll a {cf. fig. 21. IB, and Table 21. lA), is not found 

 in the spectra of fresh leaf extracts, and concluded that a mixture of the purified chloro- 

 phylls a and b is not identical with what he designated as "native" chlorophyll (a + b). 

 This conclusion was criticized by Mackinney (1940, 1941), who found, to the contrary, 

 that by mixing the two pure chlorophyll components one can reproduce the spectrum of 

 a fresh leaf extract in all its details (except, of course, for the blue-violet region, where 

 the absorption of the extracts is partly due to the carotenoids). 



Fjgiu-es 21.1 A and B show the extinction curves of the two pure chloro- 

 phyll components in ethyl ether, according to Zscheile and Comar (1941). 

 (The second figure is an enlarged detail of the first one.) 



180 

 160 

 140 

 120 

 100 



80 



60 



40 



20- 



16 



14 



10- 



640 



380 420 460 500 540 580 620 660 440 480 520 560 600 



WAVE LENGTH, m>i WAVE LENGTH, m/i 



A B 



Fig. 21.1 Extinction curves of chlorophylls a and b in ethyl ether (after Zscheile and 

 Comar 1941). Ordinates are specific extinction coefficients: log (h/I) = aspcd, where c 

 is in g./l. and d in cm. To obtain molar extinction coefficients, multiply the data for 

 chlorophyll a by 893 and those for chlorophyll b by 907. (These factors are uncertain 

 to the extent of =p 1% because of the unknown degree of hydration of chlorophyll, cf. 

 Vol. I, chapter 16.) 



