Abstract

An antibody prepared against albumin-azophenoxycholine binds tetramethylammonium and other simple aliphatic cations. In choline and acetylcholine, about half the binding is due to ion-ion interaction, and the rest to dispersion interaction. The ionic contribution is reduced in benzilylcholine and probably in the larger alkylammonium ions.

In the alkyltrimethylammonium series, binding energy increases with chain length. Similar binding energy is found with aromatic or alicyclic side chains with equivalent numbers of carbon atoms. The results are compatible with a cation-binding site lying in a pit or groove in the antibody, with the side chain associating with a superficial area.