OXIDATION, ALLOMERIZATION AND REDUCTION OF CHLOROPHYLL 1775 



in petroleum ether (blue-green solution) and at 667 m// in methanol (green 

 solution). 



AUomerization of chlorophyll a' in methanol yielded the same series 

 of pigments as that of chlorophyll a. 



Chlorophyll h also produced, l)y allomerization in methanol, several 

 products, with the principal one having absorption bands shifted toward 

 the shorter waves (to 631 and about 442 m/x in petroleum ether, 636 and 

 about 458 mju in methanol ) . 



Experiments with etiolated barley plants, immersed into chlorophyll 

 solution in methanol, showed that the chlorophyll entering the tissues is 

 rapidly deposited there in the form of green ''crystals," which upon re- 

 dissolving give no brown phase and therefore must be considered as oxi- 

 dation product. 



Once plants had liecome green, the assortment of chlorophyll pigments 

 in the leaves remains remarkably constant— in darkness as well as in light, 

 in air, oxygen, carbon dioxide or hydrogen. In the disappearance of 

 chlorophyll in ripening fruit or autumn leaves, no colored transformation 

 products of the natural chlorophylls could be observed. 



Holt and Jacobs (1954) also found that allomerized chlorophyll (or 

 chlorophyllide) a, formed by standing in air in methanolic solution, can be 

 separated by chromatography into several components. In addition to 

 the main fraction, with the spectrum of the tyj)e illustrated by Fig. 21. 4A 

 ("fraction 2"), there was one more readily absorbed fraction ("fraction 3") 

 with a spectrum practically identical Avith that of "native" chlorophyll a, 

 and a smaller, less readily absorbed "fraction 1," with a red peak further 

 toward the longer waves (c/. Fig. 37.C.3). All three fractions gave no 

 "brown jjhase" with alkali. All of them could be reduced in light by 

 ascorbic acid ("Krasnovsky reaction," cj. Chapter 35). All three fractions 

 could be reversibly decolorized (oxidized?) by ferric chloride ("Rabino- 

 witch- Weiss reaction," cJ. Chapter 16, section B3, and this section, further 

 below). Infrared spectroscopy (c/. Chapter 37C, section 2e) indicated 

 that fraction 3 alone contains the C=0 group in position 9. If negative 

 phase test is attributed to incapacity for enolization of this group, this 

 incapacity must be attributed, in fraction 3, to an oxidative substitution 

 of the H-atom in position 10, e. g., by a methoxy group: 



V III V III 



llO 9 I +CH3OH I I ^^ ^ 



(aJA.l) HC— C— C= > CH3OC— C— C= + HoO 



I II +'/'^' I II 



o o 



In fractions 2, allomerization must involve a more drastic change — 

 probably disruption of ring V, with the formation of a lactone (as suggested 

 by Fischer and Pfeiffer, 1944): 



