290 RADIATION BIOLOGY 



ultraviolet light or by the Fenton reagent. The viscosity of thymo- 

 nucleate treated by these OH radicals is diminished (Butler and Smith, 

 1950). 



On irradiation of nucleic acids with massive doses of X rays the mole- 

 cule undergoes a profound chemical change. There is ammonia forma- 

 tion (indication of ring opening in the purine or pyrimidine ring), fission 

 of glycosidic linkages with liberation of purine bases, splitting of ester 

 linkages leading to the formation of inorganic phosphate, and increase in 

 titratable acidity (Scholes et at., 1949). 



Although these studies have shown that ionizing radiations alter a 

 number of properties of the nucleic acids, the radiation dose used to pro- 

 duce these effects is far too great to explain the production of mutations 

 and the inhibition of cell division which occur with small doses of radia- 

 tion. Perhaps the nucleoproteins remain unaltered, and it is oxidation of 

 sulfhydryl groups, free and fixed groups, which is responsible for the 

 effects of small doses of radiation. 



MISCELLANEOUS EFFECTS 



When large doses of ionizing radiations are used, there occur oxidation 

 of double bonds, ruptures of rings of aromatic compounds, and reactions 

 leading to the complete destruction of the molecule. In some cases very 

 interesting polymerizations, which might be of biological importance, 

 take place. 



X-ray irradiation of benzene in aqueous solutions yields hydrogen, 

 phenol, diphenyl, traces of terphenyl, and a number of polyphenols 

 (Stein and Weiss, 1949a). Many of these reaction products are formed 

 by the action of the free radicals formed on irradiation of water. In fact, 

 hydroxyl radicals formed by Fenton's reagent (H2O2 + FeS04) are 

 capable of hydroxylating benzene at room temperature to phenol and 

 polyphenols with great ease (Cross et al., 1900). With neutrons the 

 primary ionization is the result of the action of the recoil protons formed 

 by interaction of neutrons with water molecules. Recoil protons and 

 a rays produce a much denser ionization in their tracks in the solution 

 than do X or 7 rays. The likelihood of the reactions H -|- H — > H2 and 

 OH -|- OH — » O2H2 occurring is thus greatly increased. Irradiation of 

 aqueous solutions of benzene with neutrons and a rays produces phenol, 

 diphenyl, polyphenols, and opening of the benzene ring with the forma- 

 tion of aUphatic aldehydes. The phenol must become an acceptor 

 which, when accumulated in sufficient quantities, will be attacked further 

 yielding polyphenols (Stein and Weiss, 1949b). With neutrons amounts 

 of energy much smaller than with X rays are sufficient to produce some 

 of these products. This can be attributed to the denser ionization and 



