8 PHYSIOLOGY OF NUTRITION 



Almost a third of the chlorophyll molecule is composed of phytyl, the radical 

 of phytol,! an unsaturated mono-hydric primary alcohol of the aliphatic series, 

 having the composition C20H40O and the probable structure shown by the 

 following diagram: 



CH^CH— CH— CH— CH— CH— CH— C=C CH— CH2OH 



I I I I I I I I I 



CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CHa 



Phytol is readily oxidized in the presence of air. Willstatter suggests that it 

 may be obtained from isoprene in the following way: 



4C6H8 (isoprene) + H2O + 3H2 = C20H40O (phytol). 



Carotin appears also to be related to isoprene. The phytyl of chlorophyll 

 may be replaced by the ethyl group if the leaves are treated with alcohol. 

 This replacement is effected by an enzyme known as chlorophyllase.^ 



Another alcohol radical is present in both the chlorophylls, namely, methyl 

 (CH3). They thus appear to be esters of a complex, dicarboxylic acid, one of 

 the two carboxyls (COOH) being joined to phytyl and the other to methyl. 



Regarding the complex acid forming the basis of the chlorophylls there still 

 remain some uncertainties, but it appears to be related to a tricarboxyUc acid 

 that may be represented by the formula (C3iH29N4Mg) (COOH) 3, but one of the 

 carboxyls is inactive, so that a dicarboxylic acid results. A general idea of the 

 manner in which the magnesium atom is probably related to the other compo- 

 nents of the molecule may be obtained from the following structural formula 

 for eiiophyUin, to which this fundamental acid is apparently closely related. 



CH=CH 

 CH3— C— CH C— C 



. > N<; 



C2H6— C— C C— CH 



C2H5— C=C C=C— C2H5 



Nn— Mg— N<^ ! 

 CH3— C=C C=C— CH3 



CH3 CH3 



When "the phytyl group of chlorophyll a is replaced by the ethyl group 

 (CaHs), a substance is obtained (CavHsgOeNiMg) which Willstatter called 

 ethyl chlorophyllide. This forms beautiful crystals, which were earlier mistaken 

 for pure chlorophyll. Chlorophyll b reacts in a similar way. According to the 



'Willstatter. Richard, and Hocheder, Ferdinand, Ueber die Einwirkung von Sfturen und Alkalien aat 

 Chlorophyll. I^ebig s Ann. Chem. u, Pharm. 354: ;iOS-2S8. 1907. Willstatter, Richard, Mayer, Erwiu 

 W., and Hum, Ernst, Ueber Phytol. I. Ibid. 3TS: 73-152. ign. 



2 WiUstatter, Richard, and StoU, Arthur, Ueber Chlorophyllase. Liebig's Ann. Chem. u. Pharm. 

 378: 18-72. 1911. 



