SOT.VKNT EFFECT 037 



(21.4a) ^"soi. - hv = AS + 8 



the red shift thus being decreased by the amount 8. 



Probably no other compound has been so often studied from the point 

 of view of Kundt's rule as chlorophyll. The origin of this interest was the 

 fact, first noticed by Hagenbach in 1870, that the maximum of the red band 

 of chlorophyll in living plants is displaced by about 20 mn toward tbe red 

 end of the spectmm. compai-ed to its position in solution, (lerland (1871) 

 found that a similar displacement occurs in the case of the absorption bands 

 of chlorophyll in the yellow and green. It was early suggested that this 

 position of the bands indicates a peculiar state of chlorophyll in the living 

 cell, and numerous attempts have been made to reproduce this state in 

 vitro. We will see, however, in the following review of experimental data, 

 that the "red shift" is not a specific effect, and could be caused by various 

 types of aggregation or complexing. 



We will first deal with chlorophyll solutions in different organic sol- 

 vents, and then with colloidal solutions, complexes and adsorbates, in which 

 chlorophyll is associated with proteins, lipides or other carrier;-. 



1. Solvent Effect in the Spectra of Chlorophyll and Bactericchlorcphyll 



Chlorophyll was one of the dyestuffs whose stutiy caused Kundt (1878) 

 to postulate a relation between the refractive index of the solvent and the 

 position of the absorption bands, which became known as "Kundt's rule." 

 Since then, numerous observations have been made of the spectrum of 

 chlorophyll in different solvents, e. g., by Baas-Becking and Koning (1934), 

 Hubert (1935), Wakkie (1935), Katz and Wassink (1939), Bicrmacher 

 (1939), Egle (1939) and Harris and Zscheile (1943). The agreement be- 

 tween the different authors is not very satisfactory— for example, Hubert 

 found 662.5 mju for the position of the absorption peak of chlorophyll a in 

 methanol, and 604 m/x for its position in ether, while Katz and Wassink 

 obtained, for the same solvents, 604 and 661 m^, Harris and Zscheile 664 

 and 660 mfi, and Bass-Becking and Koning 656 and 666 m/x, respectively. 



Many discrepancies probably have been caused by the use of poor 

 spectrophotometric equipment; Mackinney (1938) stressed, for example, 

 the errors inherent in the identification of the band maximum with the so- 

 called band "axis" (cf. above, page 607, and chapter 23, page 744). Other, 

 and perhaps more important, differences may have been caused by the 

 preparations used — often leaf extracts containing chlorophylls a and b 

 in unknown proportions. It is difficult enough to obtain spectroscopic 

 reproducibility even with purified preparations of a single chlorophyll com- 

 ponent! Small solvent impurities, too, may strongly change the spectrum 

 (c/. p. 647). 



