Diarmed (adamantyl/alkyl) surfactants from nitrilotriacetic acid

tThe compounds presented here constitute a clear example of molecular biomimetics as their designis inspired on the structure and properties of natural phospholipids. Thus novel double-armedsurfactants have been obtained in which nitrilotriacetic acid plays the role of glycerol in phospho-lipids. The hydrophobic arms are linked to the head group through amide bonds (which is also thecase of sphingomyelin): (R1NHCOCH2)(R2NHCOCH2) NCH2CO2H (R1being CH3(CH2)11, CH3(CH2)17,CH3(CH2)7CH CH(CH2)8, and adamantyl, and R2= adamantyl). The dependence of the surface tensionwith concentration shows the typical profile of surfactants since a breaking point, which corresponds tothe critical aggregation concentration (cac), is observed in all cases. The cac of these diarmed derivativesare about 1–3 orders of magnitude lower than those of classical monoalkyl derivatives used as referencecompounds. In contrast to conventional surfactants, reversed trends in cac values and molecular areasat the solution–

tThe compounds presented here constitute a clear example of molecular biomimetics as their designis inspired on the structure and properties of natural phospholipids. Thus novel double-armedsurfactants have been obtained in which nitrilotriacetic acid plays the role of glycerol in phospho-lipids. The hydrophobic arms are linked to the head group through amide bonds (which is also thecase of sphingomyelin): (R1NHCOCH2)(R2NHCOCH2) NCH2CO2H (R1being CH3(CH2)11, CH3(CH2)17,CH3(CH2)7CH CH(CH2)8, and adamantyl, and R2= adamantyl). The dependence of the surface tensionwith concentration shows the typical profile of surfactants since a breaking point, which corresponds tothe critical aggregation concentration (cac), is observed in all cases. The cac of these diarmed derivativesare about 1–3 orders of magnitude lower than those of classical monoalkyl derivatives used as referencecompounds. In contrast to conventional surfactants, reversed trends in cac values and molecular areasat the solution–air interface have been observed. This anomalous behavior is tied to the structure of thesurfactants and suggests that long and flexible alkyl chains should self-coil previous to the aggregation oradsorption phenomena. Above cac all compounds form large aggregates, globular in shape, which tendto associate forming giant aggregates.