Abstract
An attempt was made to synthesize dipeptide-type surfactants analogs from glutamic acid and aspartic acid, which are naturally occurring and renewable amino acids. N-Lauroylglutamic anhydride was used as a raw material for the synthesis. In this study N-lauroylglutamyl aspartic acid (LGA) and N-lauroylglutamyl glutamic acid (LGG) were prepared. Physicochemical properties such as the solubility, the lowering surface tensions, the foaming ability, the emulsification potential, and the higher order structure of the surfactant aggregates were discussed with changing the neutralization of the tri-basic carboxylic acid in the surfactants. These surfactants showed an outstanding surface tension lowering ability. Surface tension and cmc of the aqueous solution of LGA increased as the neutralization of three carboxylic acids increased. On the other hand, those of LGG didn’t show the similar behavior. This difference would result from the inequality in the hydrophobicity produced by one more methylene groups between LGA and LGG. It should bring about some changes such as electrostatic repulsion between two negatively charged carboxylate anions, the inter- and intrahydrophobic interactions and the hydrogen bonds. It was confirmed that these surfactants possessed an excellent biodegradability, a high stability for the hydrolysis, high calcium ion stability. Introduction of the peptide linkage that bonds the two amino acids did not affect the hydrolysis stability of the surfactant. Neither LGG nor LGA were hydrolyzed in basic (pH=10) aqueous solution for one month. At the same time, they showed a high moisturizing effect in addition to a low protein denaturation potential.
