MEASUREMENTS OF ABSORPTION SPECTRA OF PIGMENTS 



1799 



10-« sec. (Stupp and Kuhn); the natural life time must be r = t^/^ sec, where ,p, the 

 quantum yield of fluorescence, is about 0.25 {rf. table 87CTV). 



2. New Measurements of Absorption Spectra of Pigments in Solution 

 (Addendum to Chapter 21, Sections Al, 2) 



(o) Chlorophyll, Chlorophyllides and Pheophorbides. 



Holt and Jacobs (19540 made absolute extinction measurements on 

 the ethyl chlorophyllides a and b in ethyl ether, in the visible and the ultra- 

 violet (figs. 37C.3 and 4), from 220 to 780 niM- 



380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700 



ruyU 



Fig. 37C.3. Absorption spectrum of ethyl chlorophyllide a in ether (after Holt and 

 Jacobs 1954). Dots represent Zscheile's data for chlorophyll a. 



Similar measurements were made also with the two ethyl pheophorbides 

 (figs. 37C.5 and 6). 



According to these studies, the molar absorption curves of chlorophyll a 

 and etliyl chlorophyllide a in ether are almost identical (within ±3% in 

 respect to intensity, and ±0.5 m^ in respect to the position of the band 

 peaks between 250 and 700 m^, cf. fig. 37C.3). In the case of the b com- 

 ponent, the main peaks of the chlorophyllide appear shifted towards the 

 shorter waves by 1.5-2 mn from their position in chlorophyll, without 

 noticeable change in intensity. This corrects our earlier statement (p. 

 626), which was based on Stern's absorption curves (fig. 21.16), that the 

 absorption peaks of porphin derivatives become sharper when a short- 

 chain alcohol is substituted for phytol. 



Weigl and Livingston (1952) confirmed the finding of Katz and Wassink 

 (Vol. TI, Part 1, p. 642) that in piperidine, the absorption peak of chloro- 



