244 



6. INTERACTIONS OF INHIBITORS WITH ENZYMES 



ticularly become relatively unimportant at distances greater than 5 A, 

 when other forces are operative and the surfaces of interaction are not 

 extensive. At the usual distances of separation at equilibrium, dispersion 

 forces generally contribute significantly. It is also instructive to compare 

 the magnitudes of the total potential energy for the four different interac- 

 tions and the way in which they each vary with distance. However, it 

 should be noted that these relations are changed somewhat when interaction 

 in a dielectric occurs (see page 248). 



In dipole-dipole interactions, the relative contributions of induction and 

 dispersion forces will depend on the magnitude of the dipole moment and 

 the polarizability. Table 6-16 gives the estimated contributions for several 



Table 6-16 

 Interaction Energy Contributions for Dipolar Molecules " 



" Calculated from Margenau (1939) and Syrkin and Dyatkina (1950, p. 266). 



types of molecule. The contribution from alignment of dipoles increases 

 with the dipole moment, as does the induction effect, but the dispersion 

 contribution becomes relatively less although it may be in absolute magni- 

 tude somewhat greater. For nonpolar molecules the dispersion energy may 

 be small but it is always the sole contribution to the total potential energy. 

 The greater dispersion contribution in ethanol compared with methanol 

 is due, of course, to the greater i^olarizability of the former, i.e., the in- 

 crease in the nonpolar part of the molecule. 



A great deal of theoretical and experimental material ap])licable to 

 enzyme interactions may be found in the literature of colloid chemistry 

 and heterogeneous catalysis. One of the clearest and most comprehensive 

 reviews of intermolecular forces is that of de Boer (1950). He considers 

 particularly interactions of molecules with ionic or higly polarizable sur- 

 faces and estimates the contibutions of the various forces involved. Enzyme 

 surfaces may be occasionally rather diffuse ionic surfaces because of the 



