228 6. INTERACTIONS OF INHIBITORS WITH ENZYMES 



if it is assumed that {Jn\)i = {Jn\)2, which from Table 6-6 is seen to be 

 not unreasonable as an approximation, leads to: 



B,, =\/ B,,B,, (6-48) 



As an approximation, therefore, it is possible to evaluate By^^ and hence 

 9? from the interaction constants for the individual molecules. 



The expression for the energy, (p — — Bjd^, is the first term and the 

 most important one in a series: 



B B' B" 



Values for B, B', and B" are calculated by Margenau (1939) for various 

 molecules and, although they are probably too low, they provide an esti- 

 mate of the contribution of these higher terms. For most molecules, B' 

 is about 10% of B and B" is less than 1% of B, with respect to the contri- 

 buted energy. Thus for greater accuracy, the energy may be considered to 

 be at least 10% greater than calculated on the basis of the first — Bjd^ only. 

 It is frequently stated that these dispersion forces are nonspecific, 

 and they are in the sense that they operate between all molecules, but it 

 should be recognized that some specificity can be manifested. Since dis- 

 persion forces result from the interaction of fluctuating dipoles, the spatial 

 orientation and fundamental oscillatory frequencies of these dipoles in the 

 molecules will determine the attraction to some extent. It is likely that 

 identical macromolecules interact more strongly than unlike macromole- 

 cules (Yos et cd., 1957). Some directional dependence also may occur due 

 to the anisotropy of the polarizability. 



Multipoles 



When the distribution of charged regions in a molecule shows a higher 

 symmetry than is the case with dipoles and yet is not spherically symmetri- 

 cal, an electrical field is induced around the molecule; this field is said to 

 arise from quadrupoles, octupoles, or higher multipoles. One simple and 

 probably common situation occurs when two dipoles are opposed: 



-f - - + 



and another when the dipoles are oppositely aligned within the molecule: 



+ 



