356 PHOTOSYNTHESIS 



determination of the tremendously complex structure of chlorophyll 

 itself. The value of the work of the earlier investigators should, how- 

 ever, not be underestimated, for this was of the nature of pioneer work 

 and many of our present conceptions are based more or less directly upon 

 these early studies. 



Willstatter followed the method of breaking up the chlorophyll mole- 

 cule into smaller, simpler molecules. This was accomplished in two ways, 

 by the action of acids and by the action of alkalies on chlorophyll. These 

 two reagents yield very different products ; one of the most striking 

 differences in the action of the two reagents is that the products result- 

 ing from the action of alkali contain magnesium, while the products of 

 acid hydrolysis do not contain this element. Through the action of 

 alkali on chlorophyll the molecule is broken down successively into simpler 

 molecules containing a higher percentage of magnesium ; this element 

 is not separated from the rest of the molecule even by boiling with solu- 

 tions of alkaline hydroxides. By the action of alkalies on chlorophyll, 

 salts of chlorophyll-green color are formed, that is, the neutral chloro- 

 phyll has been converted into an acid which forms salts soluble in water. 

 Thus, the action of the alkali has split off through hydrolysis, a compo- 

 nent which in the original chlorophyll molecule was united to an acid 

 group. The first products resulting from the action of alkali have optical 

 properties which do not differ greatly from the original chlorophyll. 



Chlorophyll is very sensitive to the action of acids, the magnesium 

 is easily split out with oxalic acid and even with carbonic acid. Acid 

 affects a different part of the molecule from that attacked by alkali. 

 The former reagent does not produce an acid; hydrolysis therefore does 

 not take place. Thus, those groups which are split off by alkalies are not 

 affected by the action of acids and, vice versa, the products obtained by 

 the action of alkali contain those characteristic groups which are easily 

 destroyed by the action of the acid. The removal of magnesium from 

 the chlorophyll molecule by acid produces drastic changes in the optical 

 properties. The products formed by the action of acids are olive-green 

 to brown in color and there is very little fluorescence. From a study 

 of the products formed by the action of acids and alkalies Willstatter 

 was able to establish the molecular composition of the chlorophyll com- 

 ponents. For the details of these experiments reference must be made 

 to the original publications of Willstatter and his collaborators or to the 

 monograph of Willstatter and Stoll ; "Untersuchungen fiber Chlorophyll — 

 Methoden und Ergebnisse." 



When chlorophyll {a -\- h) is hydrolyzed with methyl alcoholic potas- 

 sium hydroxide, at the temperature of boiling methyl alcohol, there are 

 formed, among other products, the so-called chlorophyllins. There are 

 two series of these compounds, one arising from chlorophyllin, the other 

 from isochlorophyllin. These are acids, which form salts with disodium 

 phosphate, and the free acid can again be liberated by the action of 

 monosodium phosphate. Chlorophyllins are complex magnesium com- 



