BIOPHYSICAL EFFECTS 245 



more fully. Other species, such as NO and Co ++ also enhance radiation 

 effects. 



BIOPHYSICAL EFFECTS 



These can be considered as effects on molecular structure and type, with 

 the resulting effects on the physical properties of agglutination and trans- 

 port, and on the speeds of vital chemical processes. 



Agglutination or Coagulation 



Colloids — small particles, large molecules — are stabilized by electric 

 charges on their surface. At any particular pH, the acidic and basic chemi- 

 cal groups on the surface are in equilibrium with the electrolyte, and the sur- 

 face carries a net positive or negative charge. Repulsion between like 

 charges stabilizes the colloid. Further stabilization comes from water mole- 

 cules adsorbed on the polar groups of the surface, so that, from the outside, 

 the big colloid particle looks, to a particle in solution, just like a wall of 

 ordinary water molecules. 



Irradiation causes, first of all, chemical polymerization or cross-linking to 

 occur between particles. It causes changes in the polar groups, and hence in 

 the "water front" which the colloid presents to the solution. Finally it 

 causes rearrangement in acidic and basic groups such that the net surface 

 charge changes. The colloid then precipitates, or agglutinates, and becomes 

 semisolid. 



On the other hand, the colloid may be split within by radiant energy, and 

 the structure then rearranged to a form which is unstable, and it precipitates. 



Modification of Transport Properties 



Thermal Conductivity. This property is difficult to measure even under the 

 most advantageous of circumstances, and nothing is known yet about how it 

 is affected by radiation. Structural changes induced by radiation may turn 

 out to be of importance to the structural lipoproteins and collagen of the 

 skin, for example. 



Diffusion. As it was shown in Chapter 8, the diffusion coefficient depends 

 critically upon the molecular structure of the medium, with particular refer- 

 ence to the "jump distance" between rest sites in the medium and to the size 

 and shape of the diffusing species. Naturally, if the diffusing molecule is 

 broken up into small and free parts by the action of ionizing radiation, it 

 will diffuse faster. Conversely, if it or the medium becomes cross-polymer- 

 ized, diffusion will occur more slowly. 



It is expected that, as more is learned about the diffusion of water, ions, 

 and molecules through living membranes, the effects of irradiation on dif- 

 fusion will become more evident. In the absence of definitive work on this 



