COLLOIDAL AND ADSORBED CHLOROPHYLL 651 



leaves. Wakkie (1935) emulsified a chlorophyll solution in ether in a satu- 

 rated water-ether mixture, bubbled air through it and watched the changes 

 of the absorption spectrum as the ether evaporated and the chlorophyll in 

 the drops grew more and more concentrated. At a certain concentration 

 (not estimated in the paper) the absorption band began to shift to the red, 

 from 666 to 676 m^. This in(Hcates that a shift similar to that caused by 

 the accumulation of chlorophyll in colloidal particles can be produced also 

 by an increase of its concentration in true molecular solution. When the 

 ether was completely evaporated, the remaining dry chlorophyll had an 

 absorption maximum at 679 m^u. This agrees approximately with the 

 measurements of Hubert (1935), who gave 680.5 m/x for the absorption 

 maximum of solid chlorophyll (thin film of dried chlorophyll on glass). 



The possibility of energy exchange between excited and normal chloro- 

 phyll molecules and the spectroscopic effects of this exchange — which must 

 increase with increasing concentration of the pigment — will be discussed in 

 chapter 32, in connection with the concept of the "photosynthetic unit" 

 and similar hypotheses. 



A similarity between the absorption spectra of solid chlorophyll in suspension and 

 of chlorophyll in the living cell was first claimed by Ivanovski (1907, 1913). 



It thus appears that a shift of the red chlorophyll band toward the 

 longer wave lengths (approaching its position in the leaf spectrum) can be 

 achieved not only by interaction with a solvent of high polarity or polariz- 

 ability, but also by interaction with other chlorophyll molecules. This of- 

 fers several alternatives for the interpretation of the state of chlorophyll 

 in vivo. In the case of bacienochlorophyll, Katz and Wassink (1939) 

 noted that the absorption band of evaporated pigment was shifted by not 

 more than 2.5 m^ from its position in solution, while in live bacteria (and 

 in colloidal extracts from bacteria) the same band is shifted toward longer 

 waves by as much as 80-100 mn. In this case, the position of the band in 

 the spectrum of the living cells definitely indicates interaction with other 

 cell components and not merely close mutual proximity of the pigment 

 molecules. 



A "red shift" of the absorption bands of chlorophyll probably can be ob- 

 tained also by adsoi-plion on appropriate carriers: According to Seybold 

 and Egle (1940), the red absorption band of chlorophyll adsorbates on 

 starch is situated at 662 m^i, i. e., in the same region as in solution. Figure 

 21.27A, taken from Seybold and Weissweiler (1942), shows the absorption 

 peaks of chlorophylls a and b, adsorbed on sugar, in the following positions: 

 Chlorophyll a, 670 and 450 m/x, and chlorophyll b, 662 and 488 m^— values 

 that correspond to shifts by 10 and 20 m/x for the a-component and 19 and 

 35 mn for the 6-component (compared to band positions in ether). The 



