Lysine-based cationic surfactants: synthesis and study of the effect of the polar group on their biological properties

Abstract

Surfactants are surface active compounds that can adversely affect the environment. At present the main driving force behind the development of novel surfactants and emulsifiers is the search for environmentally friendly products. Due that, preparation of surfactants which mimic the structure of natural compounds such as lipoaminoacids is currently increasing because of their unique physicochemical and biological properties. We report on the synthesis, biological and physico-chemical properties of six different novel lysine-based surfactants. All of them have dodecyl fatty chains, two have a monocatenary structure and four have a gemini structure. The compounds also differ in the positive charge type, two have the positive charge in the ¿-amino group of the lysine, three in the ¿-amino group of the lysine and one have a quaternized amino group. The synthesis is a classical amino-acid condensation. The surfactant behavior has been characterized by measuring the critical micelar concentration (CMC). CMC values of monocatenary surfactants are similar to those of commercial cationic surfactants. Concerning gemini surfactants CMCs are two orders of magnitude smaller than those of monocatenaries surfactants. We have studied a number of biological properties. The hemolytic activity of monocatenary compounds is smaller than that of their gemini counterparts. Both monocatenary and gemini compounds are active against Gram-positive bacteria but not noticeable activity has been observed when bacteria are Gram-negative. After 28 days, the compounds biodegradation ratio amounts to 60% thus they fall within the category of readily biodegradable surfactants.