SPECTRA OF CRYSTALLINE AND COLLOIDAL PIGMENTS 1815 



turning to Fischer's original concept of ring III (rather than ring IV) as 

 site of the two extra H-atoms? (This would mean interchanging the 

 "short" and the "long" axes in the chlorin and bacteriochlorin systems!) 

 Fraction No. 3 may be simply the C(10)-methoxy derivative, without 

 lactone formation. In the optical spectra of several preparations of this 

 fraction, considerable variations (from 1.33 to 1.59) in the intensity ratios 

 of the blue and the red peak were noted; but all of them gave essentially 

 the same infrared spectrum. 



3. Spectra of Crystalline and Colloidal Chlorophyll Derivatives 

 (Addenda to Chapter 21, Section B2) 



The scanty data on the absorption spectra of solid chlorophyll and 

 chlorophyll derivatives (summarized in Part 1 of Vol. II, p. 649) have been 

 considerably augmented by a study by Jacobs et al. {cf. Jacobs 1952, 

 Kromhout 1952, Rabinowitch, Jacobs, Holt and Kromhout 1952, Jacobs, 

 Vatter and Holt 1953, 1954, Jacobs, Holt and Rabinowitch 1954, Jacobs 

 and Holt, 1954, Jacobs, Holt, Kromhout, Rabinowitch and Vatter 1954) 

 of the properties of chlorophylls, alkyl chlorophyllides, pheophorbides, and 

 bacteriochlorophyllide, in the form of microcrystals, colloids and mono- 

 layers. The solid preparations were obtained by diluting acetone solutions 

 of the pigments with water (occasionally, gum arable, or water-soluble 

 cellulose, was added to slow down crystal growth). Immediately upon 

 dilution (within 0.1 sec.) the red transmission minimum of the suspension 

 was observed to move (in compounds of type a) from 660 to 670 m^t; 

 fluorescence disappeared at the same time. When chlorophyll a was 

 used (in Ca++-free solvent) the band remained at 670 m/x indefinitely, 

 and no crystal formation could be observed at all. With chlorophyllide, 

 on the other hand, the transmission minimum continued to move further 

 towards the infrared; after a few seconds (or minutes), depending on 

 temperature, viscosity and concentration, it reached a final position in 

 the region of 735-745 m^. Kromhout (1952) {cf. Rabinowitch, Jacobs, 

 Holt and Kromhout 1952) was able to follow this transformation of the 

 red band by means of a rapid-action, rotating mirror spectrophotometer, 

 in which the visible spectrum was scanned within 0.01 sec. at 0.1 sec. 

 intervals by a synchronized photomultiplier-cathode ray oscilloscope- 

 photographic camera system. 



Later, similar sequences of spectra could be obtained also by ordinary 

 spectroscopy, by conducting the crystallization at 0° C. (Jacobs, Holt, 

 et al., 1954). Fig. 37C.16 shows, in graphs a and b, a sequence of trans- 

 mission spectra of growing chlorophyllide a microcrystals. Graph c 



