The relation between structure and distribution of quaternary ammonium ions in mice and rats. Simple tetraalkylammonium and a series of m-substituted trimethylphenylammonium ions.

In order to determine the relationship between structure and distribution in mono-quaternary ammonium ions, the distribution of a series of 14C-labeled tetraalkylammonium and substituted trimethylanilinium ions in mice were comparatively studied by means of whole-body autoradiography and radioassay. The partition coefficient in n-octanol/water were also determined. With tetraalkylammonium, the concentration in blood and tissues decreased in the order of tetramethyl, tetraethyl and tetrapropylammonium, which was opposite to expectation based on their partition coefficient values, but was in the order of increasing steric hindrance at the cationic head. With substituted trimethylanilinium, the concentrations in the blood, skeletal and cardiac muscles, diaphragm and salivary gland after i.v. injection to mice increased in the order: m-NO2 less than Cl less than OCH3 less than H less than CH3. This did not coincide with the order of increasing the partition coefficients, but coincided with the decrease of the Hammett sigma-constants of the substituent. These results were interpreted on the basis of the assumption that the ion-pair formation of the cationic head with an anionic site of the tissue macromolecules played an important role in determining distribution. It was pointed out that although the lipophilic character of the molecule has been often cited as the most important factor determining the distribution of the drugs, the ionic character of the molecule or of the functional group can participate as a more important factor in determining tissue distribution.