PHOTOCHEMISTRY OF BACTERIOCHLOROPHYLL 



J. C, GOEDHEER 



Biophysical Research Group, Physical histitute, 

 State University Utrecht, The Netherlands 



In the photosynthetic purple bacteria bacteriochlorophyll is the 

 primary agent which transforms the incident electromagnetic radiation 

 energy of about 1,4 ev (corresponding to a wavelength of about 880 

 mil) into sufficient electron energy to perform various chemical re- 

 actions. We therefore will look at this pigment as a possible source 

 of "high energy" electrons, 



Bacteriochlorophyll (and in green plants chlorophyll a) may act in 

 this respect in two fundamentally different ways: 



1, According to the individual model, 



2, According to the collective model. 



In the first model a chlorophyll molecule donates, as a result of 

 illumination, high energy electrons by its own chemical properties. At 

 high pigment concentration, in this model radiation energy is trans- 

 ferred by the mechanism of inductive resonance. 



In the second model the chlorophyll molecules are situated in a 

 crystalline array. Only the properties of the "crystalline" configura- 

 tion play a role in production of high energy electrons. The photo- 

 chemical properties of the individual pigment molecules are of no 

 importance. Energy is transferred by electron (or hole) migration 

 within the crystal. The second model has received much attention in 

 later years. It has the advantage of providing a mechanism for an 

 effective electron-hole separation over a distance large as compared 

 to the molecular dimensions. However, a separation between a) the high 

 energy electrons expelled from chlorophyll molecules as a result of 

 the absorption act and b) low energy electrons filling the empty space 

 in the electron configuration of the pigment molecules may also be 

 arrived at by the individual model. 



Therefore, we will consider some photochemical and chemical prop- 

 erties of bacteriochlorophyll, to investigate whether this pigment in- 

 deed is able to act as a redox system and in this way provide electrons 

 of sufficient energy content to perform photosynthesis. 



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