332 



LIGHT AND LIFE 



Trurnit (35, 71). Fig. 9 shows that the so-called amorphous solid 

 layers of chlorophyll have absorption in the 6800 A region, and when 

 the chlorophyll layers are allowed to "crystallize" the absorption spec- 

 trum moves out almost to 7200 A. Intermediate spectra of chloro- 

 phyll can be obtained, depending on the nature of the monolayers, 

 in which the peaks lie between the 6600 A peak of the true chloro- 

 phyll solution and the 7200 A peak of the crystalline chlorophyll. 



400 



800 



500 600 700 

 WAVE LENGTH -mp 



Fig. 9. Absorption spectra of chlorophyll in various states (Rabinowitch). 



Phthalocyanine as a Model for Chlorophyll Eriergy Transfer 



The ordered structure of the chloroplasts, as observed in the elec- 

 tron microscope, together with the difference in the chlorophyll spec- 

 tra in solution and in the crystalline state, were some of the things 

 which induced us to think in terms of solid lattices as a possible 

 way in which the energy, which is absorbed in the chlorophyll mole- 

 cule, might be handled in the chloroplast, and in which the oxidizing 

 and reducing power might be separated. Again, we sought models 

 of various kinds so we could experimentally develop some concepts 

 for such a separation, and here we tinned to the experiments which 

 were begini in the Soviet Union in 1949 by Vartanyan (73, 74) and 

 which were extended by Eley in England (22, 23, 24) . Eley examined 

 tlie electronic properties of crystals of a very stable molecule related 

 to chlorophyll, namely, phthalocyanine, the structure of which is 

 shown in Fig. 10. One can again recognize the tetrapyrrolic structure 



