Cationic surfactants from lysine: synthesis, micellization and biological evaluation

Abstract

Biocompatible cationic surfactants from the amino acid lysine (hydrochloride salts of N(epsilon)-lauroyl lysine methyl ester, N(epsilon)-myristoyl lysine methyl ester and N(epsilon)-palmitoyl lysine methyl ester) have been prepared in high yields by lysine acylation in epsilon position with three natural saturated fatty acids. The micellization process of these surfactants has been studied using the PGSE-NMR technique. The compounds were tested as antimicrobial agents against Gram-positive and Gram-negative bacteria. The surfactants show moderate antimicrobial activity against the Gram-positive bacteria but Gram-negative bacteria are resistant to these surfactants in the concentration range tested. The haemolytic activity is considerably lower than those reported for other cationic N(alpha)-acyl amino acid analogues. The acute toxicity against Daphnia magna and biodegradability was studied. The toxicity is clearly lower than that reported for conventional cationic surfactants from quaternary ammonium and the three surfactants from lysine can be classified as ready biodegradable surfactants.