1818 



SPECTROSCOPY AND FLUORESCENCE OF PIGMENTS CHAP. 37C 



were observed with ehlorophjdl itself, and showed the way to reUable 

 preparation of crystalHne chlorophylls a and b, and of crystalline bacterio- 

 chlorophyll (figs. 37B.6 and 7). Fig. 37C.18 gives a comparison of the 

 spectra of chlorophyll a in acetonic solution and in microcrystalline form 

 (the latter corrected for scattering!). 



Monolayers of chlorophyll, chlorophyllide and bacteriochlorophyllide 

 were obtained by Jacobs (1952, cf. Jacobs, Holt and Rabinowitch 1954) 

 by spreading on water a drop of a solution of these pigments in petroleum 

 ether. (The solubility of these pigments in pure petroleum ether is very 



Fig. 37C.18. Absorption spectrum of chlorophyll a micro- 

 crystals, corrected for scattering (after Jacobs and Holt 1954). 

 Dashed line, solution; solid line, crystals. 



small; but it can be made adequate by first dissolving the pigment in a 

 small amount of pyridine, and then adding a large amount of petroleum 

 ether.) 



The absorption spectra were obtained by picking up the monolayers on 

 glass plates. Even a single monolayer absorbs enough to permit the locali- 

 zation of the main absorption peaks; a stack of 5-10 glass plates, each 

 carrying a single monolayer, can be used to obtain a complete spectrum. 

 (Attempts to collect several monolayers on a single plate were not suc- 

 cessful.) 



Figs. 37C.19 and 20 show the absorption spectra of monolayers of 

 chlorophyll a, and ethyl chlorophyllide a. It will be noted that in chloro- 

 phyllide (and bacteriochlorophyllide) monolayers, the red band is shifted 

 toward the longer waves almost — but not quite — as far as in "large" 

 microcrystals (cf. table 37C.II). 



With chlorophyll itself, two kinds of monolayers were observed, as illus- 

 trated in fig. 37C.20. One kind — obtained from solutions containing 



