26 J. FRANCK 



are very crude, but I'd estimate that the total absorption in the new band iH about 

 a fourth of the red chlorophyll band. 



Strehler : One quarter. 



Linschitz : Maybe one fourth. You could certainly see it. 



Bassham : One thing this whole picture is based on is the assumption that 

 one (quantum transfer implies one electron transfer. Many people do not agree 

 with that assumption. I would be interested in some comments in favor of the 

 argument that one cannot transfer one electron by one light quantum. I person- 

 ally believe that you probably do transfer one electron per quantum. Franck's 

 theory would require, among other things, a minimum quantum requirement of 

 8, if you have to have two light quanta for each electron transfer. 



Rabinowitch: This obviously is not explained in this abstract because it im- 

 plies, as far as I understand, that you would need to know the energy of the free 

 radical. The transfer of one hydrogen atom creates a free radical. We usually don't 

 know what the energy of this free radical is. Franck says, "The excitation energy of 

 41 kcal. (first excited singlet state) permits only the transfer to a strong (not a 

 weak) oxidant." That must mean the energy we would assume is needed to trans- 

 fer one hydrogen or one electron to PGA or to TPN. 



Bassham: For example, the energy of 40 kcal. is equivalent to about 1.7 elec- 

 tron volts per electron. This is sufficient to make hydrogen peroxide from water at 

 a concentration of 10~* molar and at the same time to reduce TPN to reduced 

 TPN. 



Rabinowitch : You are using the average for the two hydrogens. 



Bassham : Well, do we know enough about the actual structure of grana to say 

 that it might not have some type of arrangement of semiconductors which makes 

 possible the separation of these charges, providing the electron is of the right 

 potential at the right place? I think this is certainly within the realm of possi- 

 bility. 



Gaffron: The gist of the entire discussion this morning indicates the singlet 

 state is not directly responsible for the chemical reaction. Thus you cannot work 

 with 41 kcal., you have to lower the available energy to about 30. 



Bassham : Even with 33 we can just barely make it. 



Rabinowitch: Well, that ignores the need of going over the radical state. 



Bassham: Presumably there is some system for getting around the radical 

 state to accomplish this. Reactions that in solution chemistry would require radi- 

 cals are often accomplished in vivo with much lower energy. 



Brugger : I should mention that Dr. Franck was certain that there was going 

 to be a discussion of electron transfer here. He definitely advocated hydrogen 

 atom transfer. He simply could not see his way clear to agree to electron transfer 

 in this case because, as has been mentioned, you don't have much time. If one 

 transfers electrons and makes hydrogen ions, he has to hydrate the hydrogen 

 ions, or otherwise there isn't enough energy. He felt that one hasn't enough time 

 to hydrate hydrogen ions and not enough light energy to transfer electrons with- 

 out hydrating the hydrogen ion. 



Bassham: I don't think it takes very long to transfer an electron. 



Brugger: You have to pay a penalty. The ionization potential for a hydrogen 

 atom is 13 volts. That is, 300 kcal. are required to make a hydrogen ion and an 



