22 



PHOTOSYNTHESIS 



mixture of chlorophylls a and h is used); after a short time the 

 original green colour returns. This reaction, the 'phase test^, 

 is not shown by alcoholic solutions of chlorophyll which 

 have been stored. Willstatter referred to the alteration of 

 chlorophyll due to storing as 'allomerization', and it was 

 later shown by Conant and by Fischer that this was due to 

 oxidation of the hydrogen atom in the cyclopentane ring at 



TABLE 3.2 



NOMENCLATURE OF PIGMENTS 



Ethyl chlorophyllide . 



Phaeophytin : 

 Phaeophorhide : 

 Phaeoporphyrin : 



Chlorin: 



Porphyrin : 

 Porphin: 



Chlorophyll with magnesium but ethanol 

 replacing phytol 



Chlorophyll minus magnesium 



Chlorophyll minus magnesium and phytol 



Class of porphyrins corresponding to 

 chlorophyll: they contain two hydrogen 

 atoms less than chlorophyll but still 

 contain the extra 5C ring which is lack- 

 ing in porphyrins derived from haem 



Chlorophyll minus magnesium, phytol, 

 and methanol and produced from phaeo- 

 phytins by action of alkali: the 5C ring 

 is opened. They contain tvjo hydrogen 

 atoms more than porphyrins 



Metal free tetrapyrrolic compounds de- 

 rived from haem. Also by vigorous 

 degradation of chlorophyll derivatives 



Basic metal free tetrapyrrolic structure 

 with hydrogen attached to all carbon 

 atoms I to 8 



Cio by atmospheric oxygen. The 'phase test' is shown by 

 compounds containing an intact cyclopentane ring. Thus 

 phaeophytin and protochlorophyll (see later) also give the 

 phase test. During saponification the cyclopentane ring is 

 opened by hydrolysis, thus producing a chlorin which in the 

 absence of oxygen can be converted back again to the 

 original compound with a closed ring. In the presence of 

 oxygen the side chains undergo oxidation and give a variety 

 of chlorins. 



