Σύνθεση - χαρακτηρισμός - επιφανειοδραστικές ιδιότητες - εφαρμογές νέων τασενεργών ενώσεων παραγώγων της γλυκερίνης με αμινοξέα

Abstract

Three homologous series with alkyl chains of 10-16 carbon atoms as hydrophobic part conjugated via an ether bond to the glycerol skeleton and the amino acids phenylalanine, histidine and tyrosine conjugated also to the glycerol via an NH bond were synthesized and characterized. The hydrophilic moiety is the carboxylic group of the aromatic amino acid, classifying consequently the whole family to the soap- type amphiphiles. The new surfactants are white clystalline solids prepared in a two steps procedure with very good yields. The availability of the applied simple synthetic procedure with aromatic amino acids in contrast to aliphatic amino acids that failed to give analogous derivatives was attributed to the complexation of the amino acid aromatic moiety with alkali ions stabilizing favorable conformations for substitution reaction. Their characterization was assigned by IR, 1H NMR, 13C NMR, and elemental analysis. The surface properties, as are the critical micelle concentration (CMC) and the surface tension corresponding to this concentration (γCMC ) were measured by Wilhelmy plate technique and from these data the log of surfactant concentration required to reduce the surface tension of the solvent by 20mN/m (pC20) and the minimum interfacial area occupied by the surfactant molecules (Amin) were calculated and compared to the conventional soaps as well as to the members of the homologous series between them. The differences that observed are attributed to the length of hydrophobic alkyl chain in combination to the amino acid. Thus, all members of the three homologous series possess significantly lower critical micelle concentrations and surface tensions corresponding to these values compared to the typical soaps, as well as to conventional anionic surfactants. A very interesting result was taken also from the significantly lower area per molecule of surfactants with the amino acid tryptophan (literature) in contrast to all the rest with the amino acids phenylalanine, tyrosine, histidine. A suggestion was made that the more condensed packing of tryptophan derivatives at the water air surface is due to a different orientation of these molecules where the indole works as a polar headgroup with the NH directing toward the water face in agreement with the known peculiar role of tryptophan residues in stabilizing membrane proteins. The new amphiphiles are supposed to be ecological because they possess the glycerol skeleton and an aromatic amino acid, both existing in natural products and consequently available from renewable sources. They also have a biodegradable linear alkyl chain. Given their biocompatibility and their solubility in vegetable oils, they are promising candidates as emulsifiers for several food, cosmetic and pharmaceutical applications. Given also their solubility in alkaline water, they are proper as wetting and cleansing agents. So, they were tried as cosurfactants in O/W emulsions (10/90 v/v) using as oil phase corn oil and as emulsifier glycerol monostearate (GMS). The new cosurfactants enhanced…