Colloidal association and biological activity of some related quaternary ammonium salts

Abstract

Two series of cationic surface-active agents, benzyldimethylalkylammonium chlorides and 4-nitrobenzyldimethylalkylammonium chlorides, where the alkyl group varies from a 6-carbon-atom straight chain to an 18-carbon-atom straight chain, have been prepared. The critical concentration for the formation of micelles has been measured by the dye method for each member of each series. As has been discovered in other cases of long-chain compounds (9, 10), here too there exists a linear relation between the number of carbon atoms in the alkyl group and the logarithm of the critical micelle concentration. A third series of cationic surface-active agents has been prepared, similar to the series above save that the variation in structure is obtained by varying the nature or position of the substituent in the benzyl group, while the alkyl group is lauryl throughout. The critical micelle concentration of each member of the series has been measured by the dye method. The critical micelle concentration thus obtained varies with the polarity of the benzyl portion of the molecule. Measures of this polarity are provided by the boiling points, melting points, dielectric constants, or dipole moments of the toluene compounds that correspond to the benzyl portions of the quaternary ammonium salts. It is found that the critical micelle concentrations of the quaternary ammonium salts are proportional to the square of the dipole moment of these corresponding substituted toluenes. Correlations with microbiological activities of these quaternary salts have been attempted.