FLUORESCENCE OF CHLOROPHYLL 171 vUvO 1827 



Coagulation by magnesium chloride caused a shift of the absorption in- 

 tensity toward the longer waves (and a sharp increase in scattering). 

 Colloidal solutions of crude bacteriochlorophyll exhibited only one peak. 



These observations show obvious similarity to the above-described 

 findings of Jacobs et al. Krasnovsky's interpretation was somewhat 

 different; he did not inquire into crystallization, and considered the two 

 absorption peaks of the films at 800 and 850 m^ (and the possible third 

 peak at 890 mn) (as well as the several peaks in bacteria located at ap- 

 proximately the same wave lengths, cf. below, section 6(c)), as belonging 

 to different "states of aggregation" of bacteriochlorophyll. {In vitro, the 

 several bands obviously cannot be attributed to association with different 

 proteins^ — or other foreign molecules— as was suggested by Katz and 

 Wassink for the three bacteriochlorophyll bands in vivo, cf. Vol. II, 1, p. 

 704, and below, section 6(c).) 



The band at 790-800 m/x, nearest to the "monomer" band (located in 

 organic solvents, at 750-770 m^), corresponds, according to Krasnovsky 

 and co-workers, to a relatively low state of aggregation, while the bands at 

 850 and 890 mju are attributed by them to states of higher aggregation. 

 The three states may differ not only in the size of the particles but also in 

 nature of their bonding. (It was suggested, for example, that in "BChl 

 800," association occurs via the magnesium atom, while, in "BChl 850," 

 it occurs through some other group — because only the "850" form was 

 observed in bacteriopheophytin.) 



Comparison with the results of Jacobs on methyl bacteriochlorophyllide 

 and bacteriochlorophyll (table 37C.II) leads to the suggestion that the 

 840-850 mju band may belong to a crystalline phase, and that at 790-800 

 mju to a noncrystalline, "colloidal" phase. The relation between the bac- 

 teriochlorophyll peaks at 750-770 m^ (solution), 790-800 m/x (colloid) and 

 840-850 m/i (crystal) would then be analogous to that between the chloro- 

 phyll peaks at 660 m^ (solution), 670 m^ (colloid) and 735-740 mju (crystal- 

 line precipitates and monolayers). The nature of the "890" form remains 

 open, but one could think of analogy with the "high density" forms of 

 chlorophyll. 



Whether the several bands of bacteriochlorophyll in vivo can be inter- 

 preted in the same way as the several bands in vitro will be discussed in 

 section 6(c) below. 



4. Fluorescence of Chlorophyll in vitro 



(Addendum to Chapter 23) 



French (1954) described the fluorescence spectra of several photosynthe- 

 tic pigments in vitro and in vivo, obtained with a highly sensitive recording 



