Lysine-based surfactants

53 Lysine-Based Surfactants 53,1 Structure and Synthetic Aspects 

Amino acid-based surfactants constitute an important class of natural surface-active biomolecules of great interest to organic and physical chemists as well as to biologists 

The structure of these nonionic amphiphilic compounds is based on A ,A -diacyl lysine and contains no active hydrogen in the ethylene oxide (EO) hydrophilic head (they possess a methoxy capped EO chain), with the result that they are more chemically 

Biocompatible cationic surfactants from the amino acid lysine (hydrochloride salts of A -lauroyl-lysine methyl ester, IV -miristoyl-lysine methyl ester and A -palmitoyl-lysine methyl ester) show moderate antimicrobial activity against the Gram-positive bacteria. The haemolytic activity of these compounds is considerably lower than those reported for other cationic Ai -acyl amino acid analogues [64]. Taking into account the high biodegradation level and the low haemolytic activity, these compounds could be considered safe surfactants in relation to the cell of the human body. These properties make them suitable candidates for biological and medical applications [65]. 

Gemini surfactants show greatly enhanced surfactant properties relative to the corresponding monovalent compounds, which makes them of special interest for biomedical applications. In the last 10 years different gemini cationic surfactants with amino acids 

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Most of the lysine-based surfactants are A -acyl lysine (Figure 5.3, 1) or A -acyl lysine (Figure 5.3, 2) salt or ester derivatives. 

Figure 5.2 Schematic structure of lysine-based surfactants.

In this chapter, the development and usefulness of many amino acid- and protein-based surfactants has been discussed. The cost of amino acids and proteins and complicated manufacturing processes were the prohibiting factors for the broad utilization of this class of surfactants. Large-scale production and market consumption of certain amino acids, such as glutamic acid and lysine, have helped to alleviate this limiting factor. 

Very recently, the self-assembly of poly(y-benzyl-i,-glulamalc)-fo-poly(i,-lysine) rod-coil copolypeptide via ionic complexation was reported by Ikkala, Hadjichristidis and coworkers [65]. Complexation between the anionic surfactants dodecyl benzenesulfonic acid and the cationic poly(L-lysine) chains occurs via proton transfer from the acid group to the base, resulting in electrostatically bonded comb-like structures, and fluid-like liquid crystalline structures at room temperature due to efficient plasticization of dodecyl benzenesulfonic acid. 

FIG. 8 Structures of amino acid-based gemini surfactants as exemplified by lysine. 

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