83 



that the energy will be as efficiently used because, after all, there will be a 

 larger amount of energy dissipated thermally in a case like that. However, it 

 may very well be true that a very large fraction of the excited molecules ends 

 up this way. That is quite different from the suggestion of uniformly very high 

 energy efficiency. That is correct, isn't it, Dr. Linschitz? 



LINSCHITZ: Yes. I want to talk later about the process of energy transfer. 

 The main point I want to make at this stage is this: Here is a way in which one 

 can introduce radicals possibly in strategic places in the protein or nucleic acid 

 part of the cell without the expenditure of as much energy as is necessary to 

 form these radicals by ionization and subsequent processes. 



While I am on this point I might mention another possible way of getting 

 radicals cheaply into the cell. That involves the excitation of heavy metal com- 

 plexes which exist in the cell, again in relatively small concentration but yet 

 again possibly in vital places in the cell. Many heavy metal complexes exist 

 which have intense absorption hands comparable to those of dyes (8). In some 

 cases, these bands may even lie in the visible. Excitation of these complexes 

 certainly involves electron transfers within the complex which may again lead 

 to free radicals with relatively low energy expenditure. Thus, a typical case 

 would be (9): 



+ + + + ++ ++ ++ + + 



(Fe OH') (Fe OH) — ^Fe + OH' 



On this whole matter of the energy which is necessary to introduce radicals 

 into the system, I should like to show some evidence that this energy may real- 

 ly be very small even for molecules of not too high a degree of complexity. 

 This is based on work of G.N. Lewis and his group in which direct photo-oxida- 

 tion processes were studied. 



Lewis and Lipkin (10) were able to demonstrate the formation of known 

 semiquinones or radical-ions of certain organic molecules (aromatic amines, 

 phenols, dyes, etc.) when these substances were illuminated in glassy solvents 

 at low temperatures. Thus, they postulated that processes of the following type 

 occurred: 



RH hv > RH- + + e, 



which might be followed by 



RH- + ► R- + H + , 



since the spectra of RH' or R' were found in the glass after illumination. By 

 using suitable solvents (containing amines of low molecular weight) we have been 

 able recently to demonstrate the existence in the illuminated glass not only of 

 the absorption bands of the organic radical but of the solvated electron as well 

 (11). In the solvents we used (mixtures of iso-pentane, triethylamine and meth- 

 ylamine) the solvated electron absorption appears as a broad band starting at 

 about 7000 A and extending into the infrared at least as far as 14, 000 A. There 

 is thus no doubt that the photo-ionization (or photo-oxidation) process suggested 

 by Lewis and Lipkin does occur in organic solvents. 



When the rigid solvent is softened by warming slightly, the absorption bands 

 of organic radical and electron both disappear together, and the spectrum of the 

 original organic molecule is restored quantitatively. This recombination proc- 

 ess is frequently accompanied by light emission and we have established that 

 this luminescence is identical with the normal phosphorescence of the original 



