440 CHLOROPHYLL CHAP. 16 



phytol is an almost saturated compound and, because of the absence of conjugated 

 double bonds, it is a colorless oil, not a pigment. The same factor deprives the phytol 

 molecule of rigidity; it can be twisted or bent without strain. 



CHa CH2 CH2 CH2 CH2 CH2 CH 



2 



CH CH2 CH CH2 CH CH2 C=CH-CH20H 



I I I I 



CH, CH, CH, CH 



3 



Formula 16.1. Phytol (C20H39OH). 



The two chlorophylls can be formulated as phytyl-methyl chloro- 

 phyllides: 



C20H39OO C20H39OO 



C,2H,oON4Mg C32H2802N4Mg. 



CH3OO CH3OO 



chlorophyll a chlorophyll b 



Willstatter found that plants contain an enzyme, chlorophyllase, which, 

 in the presence of methanol or ethanol, causes the exchange of phytol 

 for these short-chain alcohols (c/. Chapter 14, p. 377). The resulting 

 products, the methyl (or ethyl) chlorophyllides, are more easily crystalliz- 

 able than the chlorophylls, but similar to them in many other properties, 

 e. g., spectrum. (Borodin 1882 and Monteverde 1893, first described 

 them as "crystalUne chlorophyll.") 



Experiments on the degradation of chlorophyll have shown that 

 chlorophyllin contains four pyrrole nuclei: 



HC CH 



HC CH Formula 16.11. Pyrrole (C4H5N). 



\ / 

 N 

 H 



and one atom of nonionizable magnesium, probably situated in the center 

 of the molecule. The oxygen atoms unaccounted for by the two carboxyl 

 groups belong to carbonyl groups (one in chlorophyll a, two in chloro- 

 phyll 6). 



It has been mentioned that a relationship between chlorophyll and 

 hemin has been considered probable since the time of Verdeil (1851). 

 Willstatter showed that hemin, too, contains four pyrrole nuclei, arranged 

 around an iron atom. Apart from this difference in metal, the formula 

 of chlorophyllin a differs from that of hemin only by one additional 

 oxygen atom. In 1913, Willstatter and StoU rejected as improbable a 

 structural formula of hemin, suggested a year earlier by Kiister (1912). 

 which later proved to be fundamentally correct. It showed the four 

 pyrrole nuclei linked by four =CH— bridges into one large ring system. 

 Willstatter and Stoll thought that a closed ring containing twelve carbon 



