464 



CHLOROPHYLL 



CHAP. 16 



chlorophyll-protochlorophyll appears as a possible reversible oxidation- 

 reduction system in the living cell, no proof of the reversibility of this 

 (or any other dihydrophorbin-phorbin) system has as yet been obtained 

 in vitro. 



Another reaction which must be mentioned here is that of chlorophyll 

 with, ferric chloride, described by Rabinowitch and Weiss (1937). When 

 ferric salts are added to a methanol solution of chlorophyll (or alkyl 

 chlorophyllide), the solution instantaneously changes its color from green 

 to yellow. Spectroscopic observation of the product shows (cf. Fig. 

 51a) a practically complete disappearance of the red absorption band. 



>» 

 I 



o 



6200 



6400 



5600 



6600 A 



400 



480 



560 



640 



Fig. 51. — Spectrum of "oxychlorophyll" (after Rabinowitch and Weiss 1937). 



a. Disappearance and restoration of the red band of ethyl chlorophyllide a in 

 methanol. 



• before the reaction; ▲ immediately after the reaction with ferric chloride; A 

 after restoration by ferrous chloride; O after restoration by excess sodium chloride; 

 n after standing. 



b. Disappearance of the red band of chlorophyll a in methanol by the addition 

 of increased quantities of eerie ammonium nitrate (beginning with 1 mole eerie salt per 

 mole chlorophyll in curve 1 and ending with 12 moles per mole chlorophyll in curve 5). 



The yellow solution can be changed back into the green form by the 

 addition of ferrous chloride or another reductant. If this restoration is 

 carried out immediately, the extinction curve of the restored product is 

 identical with that of the original chlorophyll, the "phase test" is 

 unimpaired, and the reaction with ferric chloride can be repeated again. 



