1776 CHEMlSTllY OF CHLOROPLAST PIGMENTS CHAP. 37B 



V III III 



llO 9 I +CH3OH I I 



(37A.2) HC— C— C= > CH3OC— O— O— C— C= + H,0 



I II +1V2O2 I II 



o o 



The difference between the fractions 2 and the (small) fraction 1 re- 

 mains to be interpreted. 



The chlorophyll reaction with ferric chloride, described by Rabino- 

 vvitch and Weiss and interpreted by them as oxidation (Vol. I, p. 464), 

 also was studied by Strain (1949). He noted that extraction of the yellow 

 product with water and petroleum ether led to regeneration of chlorophyll 

 a, and that addition of dimethylaniline prevented the formation of the yel- 

 low product. He concluded from these observations that the reaction in 

 ciuestion is not an oxidation. However, the interpretation of Rabinowitch 

 and Weiss was based on the assumption of an equilibrium between the re- 

 duced and the oxidized form — and in this form their hypothesis is not 

 contradicted by Strain's observations. 



Strain confirmed that the decoloration reaction with ferric chloride 

 occurred also in allomerized chlorophyll a, and in the above-described 

 green product of enzymatic oxidation in chopped leaves. 



Objections against the interpretation of the reaction of chlorophyll with 

 ferric salt as reversible oxidation were raised also by Ashkinazi, Glikman, 

 and Dain (1950). They noted that bleaching of the red al)Sorption band of 

 chlorophyll in methanol can be caused not only by Fe+^ salts, but also by 

 the salts of Al+^ and Sn+" (while Cu^^ and Zn+2 caused an enhancement of 

 the red band, and K+, Ca+'-, Pb+'' and Mn+2 had little or no effect). The 

 authors suggested that the bleaching effects of Al+^, Sn+- and Fe+^ are 

 caused primarily by the acidity of these salts, which leads to pheophytiniza- 

 tion of chlorophyll (and conseciuent weakening of the redbandandincreasein 

 absorption in the green). The ions Fe+^, Cu+- and Zn+- (but 7iot Sn+- 

 and Al+^) react with pheophytin, replacing hydrogen and forming metal 

 complexes; in these complexes, the red band is restored to the same (or 

 even greater) intensity it had in chlorophyll. Ashkinazi et al. suggested 

 that a similar complex, but with a much weaker red band, is formed also 

 by pheophytin with Fe+^ ions; the Rabinowitch- Weiss "reversible oxida- 

 tion" was thus reinterpreted by them as conversion of Mg-pheophytin 

 (chlorophyll) into olive-green pheophytin, followed by formation of greenish- 

 yellow ferripheophytin complex, or a bright green ferropheophytin com- 

 plex. Ashkinazi and Dain (1951) prepared a pheophytin-ferrous iron com- 

 plex by heating ferrous acetate with pheophytin (a -|- h) solution in acetic 

 acid, extracting with chloroform, evaporating to dryness, washing out the 

 iron salt and dissolving in ethanol. Exposure to air caused oxidation of the 



