EFFECTS OF THE DIELECTRIC CONSTANT 



805 



by Fuoss and Kraus (1933) for the dissociation of tetraisoamylammonium 

 nitrate in dioxane-water mixtures. If the logarithm of the dissociation con- 

 stant is plotted against I ID (using bulk dielectric constants), the curve 

 shown in Fig. 15-16 is obtained. It may be seen that this is linear over 

 most of the range and deviates only at very low dielectric constants (in 

 mixtures where the water is less than 2%). The slope of the linear portion 



Fig. 15-16. Effects of the dielectric constant (water-dioxane mixtures) on the dis- 

 sociation constant of tetraisoamylammonium nitrate, using bulk dielectric constants. 

 (From Fuoss and Kraus, 1933.) 



of this curve is approximately 33 and thus d^ may be calculated to be 

 6.45 A. Now this distance is smaller than that calculated on the basis of 

 the closest approach of these two ions, which would be between 9-10 A. 

 It would appear that a more reasonable value for the equilibrium distance 

 would have been obtained if microscopic dielectric constants had been 

 used. In fact, these results indicate that the effective dielectric constant is 

 approximately 70% of the bulk dielectric constant, which is actually about 

 what one would predict at a separation of 9 A. 



For most interactions of an inhibitor with an enzyme involving ionic 

 or diiDolar groups one would anticipate that the variation of the inhibitor 

 constant if, with the dielectric constant would be as described above, but 



