Masahiro Takehara

Properties and applications of amino acid based surfactants

Abstract Amino acid based surfactants, which have an amino acid residue as a hydrophilic moiety, are reviewed with respect to their properties and applications. Salts of N α -acyl amino acids have an amino acid side chain radical in the hydrophilic moiety, an amide linkage and a chiral carbon atom, and show different characteristics when compared with fatty acid salts. Salts of N -acyl-L-glutamic acid, N α -cocoyl-L-arginine ethyl ester, N ϵ -lauroyl-L-lysine, and N -lauroyl-L-glutamic acid α,γ-dibutylamide are detailed.

Surface active N-acylglutamate: I. Preparation of long chain N-acylglutamic acid

Long chain N-acylglutamic acid was prepared in a high yield by a reaction of glutamic acid with fatty acid chloride in a mixed solvent of water and a water miscible organic solvent such as acetone, methyl ethyl ketone, dioxane, tetrahydrofuran,t-butyl alcohol or cyclohexanone. In this reaction the composition of the mixed solvent influenced the yield of N-acylated glutamic acid and the best yield was obtained when the reaction was carried out in the mixed solvent comprising 30–60% v/v of the organic solvent. Long chain N-acylaspartic acid was also obtained in a high yield by the same method. As the other method to obtain N-lauroyl-D L-glutamic acid, it was examined that N-acyl-α-aminoglutarodinitrile which was obtained by a reaction of α-aminoglutarodinitrile with fatty acid chloride was hydrolyzed with an aqueous alkaline solution. The salts of long chain N-acylglutamic acid are known as the surface active agents that react mildly on the human skin.

Surface active N-acylglutamate: II. Physicochemical properties of long chain N-acylglutamic acids and their sodium salts

The physicochemical properties of long chain N-acylglutamic acids (AGA) and their sodium salts (AGSn) are described. The solubility, Krafft point, pH value, critical micelle concentration, surface tension and foaming power were measured. The properties of the optically active AGA or AGSn differed from those of the corresponding racemates, especially in solubility. The monosodium salts generally had high Krafft points, but monosodium N-oleoylglutamate had a low Krafft point. The monosodium salts hydrolyzed in the diluted aqueous solution to liberate the AGA. The aqueous solutions of the monosodium salts had low surface tensions and good foaming properties. The disodium salts were highly soluble in water, while surface tensions and foaming properties were inferior to those of the corresponding monosodium salts.

New amphoteric surfactants derived from lysine. I. Preparation and properties of Nε-acyllysine derivatives-acyllysine derivatives

New amphoteric surfactants were prepared from Nε-acyllysine which was obtained by the thermal dehydration of a higher fatty acid salt of lysine and was not soluble in water. Nα,Nα-dimethyl-Nε-acyllysine was prepared by the catalytic reductive condensation of Nε-acyllysine ester with formaldehyde in good yield. Nα,Nα,Nα-trimethyl-Nε-acyllysine was obtained from the reaction of Nα,Nα-dimethyl-Nε-acyllysine ester with methyl iodide. Confirmation of the structure of these derivatives was obtained by spectrometric and spectroscopic analyses.The solubility of Nε-acyllysine was improved significantly by the introduction of Nα-methyl groups. Physicochemical and surface active properties of the derivatives were investigated in terms of isoelectric points, dissolution temperatures, surface tensions, critical micelle concentrations (cmc), foaming properties and wetting powers. Nα,Nα,Nα-trimethyl-Nε-acyllysine had lower dissolution temperatures than Nα,Nα-dimethyl-Nε-acyllysine. The latter showed lower surface tensions than the former at cmc. Nα,Nα-dimethyl-Nε-lauroyllysine was best in wetting power and foaming property.

Surface-Active N-Acylglutamate. IV. Physicochemical Properties of Triethanolamine long chain N-acylglutamates

The physicochemical properties of triethanolamine long chain N-acylglutamates are described. The monotriethanolamine salts were less soluble in water and superior in surface activity, compared with the corresponding ditriethanolamine salts. The monotriethanolamine salt showed weak acidity in an aqueous solution. There were some differences between optically active and racemic N-acylglutamates, especially in the values of critical micelle concentration.

Surface active N-acylglutamate: III. Physicochemical properties of sodium long chain N-acylglutamates

The physicochemical properties of sodium long chain N-acylglutamate (AGSn) are described. The wetting power, emulsifying power, dispersing power and calcium ion stability were measured. Monosodium N-lauroyl-l-glutamate (l-LGS) had good wetting and emulsifying properties, but disodium N-acylglutamate (AGS2) was inferior tol-LGS in those properties. In the dispersing power using carbon black as powder,l-LGS was inferior but AGS2, having a palmitoyl or stearoyl radical, was excellent. The AGSn with a few exceptions had good calcium ion stabilities.