234 



6. INTERACTIONS OF INHIBITORS WITH ENZYMES 



interaction distances in solution would be somewhat greater. Lastly, in 

 interactions of molecules with proteins, it is likely that all of the groups 

 are not able to come into close contact, due to other types of forces or 

 steric factors; parts of the molecule would thus be at greater distances 

 from the protein groups than predicted on the basis of equilibrium dis- 

 tances and would contribute less than expected to the interaction energy. 

 The van der Waals' radii should probably be taken as the values for the 

 closest approach of atoms assuming the attractive forces here considered. 

 Approximate van der Waals' radii for some important groups are given in 

 Table 6-9. It is evident that these radii are not spherically symmetrical and 

 that the radius used must depend on the assumed configuration of the 

 interacting molecules (Fig. 6-7). 



Table 6-9 



Van der Waals' Radii of Groups and Molecules "^ 



" These radii are estimated from the atomic van der Waals' radii in Table 6-8 and 

 the group configurations shown in Fig. 6-7. They should be considered as minimal val- 

 ues and the interaction distances calculated from them must be taken as the measure 

 of closest approach, the actual interaction distances, for various reasons, often being 

 greater. The designation " head-on " refers to a direction directly opposite to that of 

 the bond between the group and the rest of the molecule; " side-on " refers to 

 the distance of closest approach from the side of the group; " along X-Y " refers to 

 the direction of the bond indicated. 



