ISOMERS AND SOLVATES OF CHLOROPHYLL 1771 



below, and considered it a side product of evolution of Mg vinyl pheo- 

 porphyriii as, as indicated in fig. 37B.4.) Granick saw in the same light 

 the role in photosynthesis of the phycobilins, which he considered another 

 survival from an early stage of evolution. 



This approach differs, in its general tendency, from the theoi-ies that 

 consider organic evolution as having been accompanied by a loss of syn- 

 thesizing abilities rather than by their gradual aquisition. Also, Granick 

 sees the role of accessory pigments in somewhat different light than the — 

 presently most plausible — hypothesis that these pigments serve as sup- 

 pliers of energy, by resonance, to the one pigment adapted for the photo- 

 catalytic function proper — chlorophyll a {cf. Chapters 30 and 32) . 



3. Isomers and Solvates of Chlorophyll 

 (Addendum to Chapter 15, section Bl) 



In \'ol. I, page 403, we mentioned that Strain and Manning (1942) 

 had observed the reversible conversion of chlorophylls a and h into slightly 

 different forms, which they called a' and b'. (It will be recalled that four 

 such forms: d, iso-f/, d' and iso-r/' were observed with chlorophyll d.) 

 Strain (1949, 1953) gave additional details on these compounds. 



When chlorophyll is extracted from leaves, hydrolytic and oxidative 

 reactions are apt to occur, leading to a multiplicity of colored bands in the 

 chromatographic column. The relative rates of these reactions depend on 

 the plant species used, and on incidental factors such as the method of 

 mincing (for example, chopping causes less oxidation than grinding or 

 crushing). Light is to be avoided during preparation and storage of the 

 minced leaf material. 



Rapid extraction of chopped mallow or barley leaves by grinding in 

 methanol or acetone, to which some petroleum ether had been added, gives, 

 according to Strain, only chlorophylls a and b. If, however, chopped leaves 

 are placed into boiling water foi- 1-2 minutes before extraction, a' and b' 

 are also found in the extract. (Plants with acid sap, such as Opuntia, 

 Pelargonium, and Bryophyllum, rapidly form pheophytin when heated in 

 air.) Chopped leaves, dried in air for 24 hours, yield small amounts of 

 a' and 6' ; heating to 100° C. in air for 15 minutes after drying increases the 

 quantity of these isomers considerably. No new pigments are produced, 

 in either mallow or barley leaves, by freezing and thawing, or by standing 

 with saturated ammonium sulfate for 20 hours and wasliing (by dialysis 

 into distilled watei') for 20 hours. 



Isomerizations similar to those occurring with chlorophylls a and b 

 can be produced also with the chlorophyllides, e. g., by heating their pro- 

 panol solutions, or permitting them to stand for several days at room tern- 



