The results obtained in the study of these
antagonists show that the assumptions of Barlow, Scott
and Stephenson (1963), that affinity is made up of components which are additive, is far too simple. An
extreme example is the effect of replacing esters
(—CO—0—) by ethylene (-CH₂CH₂-); in the monophenyl
series this increases affinity whereas in the diphenyl
series it decreases affinity. On the other hand, there
is no obvious relationship between the effects of substituents on affinity and the affinity itself. It
appears, rather, that effects of changes in structure on
affinity are related to the chemical nature of the compounds and within series, for example, within the "lower
analogues" or within the "higher analogues", the effects
do follow a regular pattern, indicating that the binding
is made up of components which are additive. The
differences between the series, however, indicate that
different types of molecule bind in different ways and
even within series it appears that there are slight
differences in the ways in which the individual compounds
become bound
