1838 SPECTROSCOPY AND FLUORESCENCE OF PIGMENTS CHAP. 37C 



in chapter 37B, section 6). Purified bacteriochlorophyll has no visible 

 fluorescence, while the green oxidation product fluoresces red. 



French (1954) made similar observations: A two-band fluorescence 

 spectrum was found in a "crude" bacteriochlorophyll preparation; after 

 chromatography a green fraction was separated which gave only one 

 fluorescence band, at 687 mn. However, the main blue fraction still 

 showed, in French's experiments, the two original bands. Their relative 

 intensity depended on the wave length of the exciting light, confirming the 

 surmise that they belonged to two different compounds, in other words, 

 that the blue fraction still was a mixture rather than a pure pigment. 



French (1954) gave also a spectral curve for the fluorescence of proto- 

 chlorophyll in acetone. It showed a main peak at 630 m/i and a secondary 

 peak at 685 m^i. 



(h) Fluorescence of Phycobilins 



Bannister (1954) found that the quantum yield of fluorescence of the 

 purest phycocyanin preparations (i. e., preparations freed as much as 

 possible from adventitious proteins), excited with monochromatic ultra- 

 violet light, was constant (within 10%) from 250 to 400 m/z, including 

 the region around 275 mju, where a considerable fraction of the absorbed 

 light must be assigned to the protein moiety of the chromoprotein molecule, 

 more specifically, to tryptophane and tyrosine residues. (Crude estimates 

 indicated the protein share of the absorption in this region to be of the 

 order of 50%.) This indicates an efficient excitation energy transfer 

 from the protein to the chromophore — a type of energy transfer suggested 

 before as explanation of CO-removal from hemoproteins by light absorbed 

 in their protein moiety. In the latter case, however, an alternative to 

 transfer of electronic excitation is conceivable: the conversion of elec- 

 tronic excitation into vibrations, and accumulation of enough vibrational 

 energy in the iron-carbon monoxide bond to dissociate it; no such alterna- 

 tive explanation seems to be possible in the case of protein-sensitized 

 fluorescence of phycobilins. 



5. Chemiluminescence of Chlorophyll in vitro and in vivo 



The only evidence of chemiluminescence of chlorophyll, described in 

 Part 1 of Vol. II, was the light emitted, upon heating, by solutions of 

 chlorophyll in tetralin (p. 751). Since then, two studies have been de- 

 veloped in this field. One deals with a system in vitro, the other with 

 photosythesizing cells. 



Linschitz and co-workers (1952) found that chlorophyll (and other 

 metalloporphyrin dyes) chemiluminesce when reacting with organic per- 



