The mode of action of N-(n-Dodecyl)diethanolamine with particular reference to the effect of protonation on uptake by Escherichia coli.

In a homologous series of N-(n-alkyl)diethanolamines antimicrobial activity was related to surface activity and increasing octanol-water partition coefficient. Maximum activity was exhibited by the dodecyl-, tetradecyl- and hexadecyl-derivatives. Dodecyldiethanolamine (DDE) displayed a broad spectrum of activity. Towards Escherichia coli NCIB8277, its bacteriostatic and bactericidal activity increased as the degree of protonation lessened, and may have been influenced by the formation of micelles. Uptake of DDE by washed suspensions of E. coli was more rapid and more extensive at pH 7.0 than pH 4.0. Within this pH range, bacterial uptake, the octanol-water partition coefficient (lipid solubility) and the proportion of unprotonated DDE all increased. Uptake isotherms at pH values in the range 4.0 to 8.0 are interpreted as signifying different uptake mechanisms for the protonated and unprotonated forms.