Preparation, surface activities, and aggregation behaviors of N-acyl oligopeptide surfactants based on glycylglycine and glycylglycylglycine

With the growing concern about safety and environmental issues, amino acid-based surfactants have great potential as sustainable and eco-friendly substances. In the present study, six N-acyl oligopeptide surfactants were synthesized using fatty acid methyl esters (i.e., methyl caprate, methyl laurate, and methyl myristate) and glycyl oligopeptides (i.e., glycylglycine and glycylglycylglycine). Surface active properties and aggregation behaviors of these surfactants were investigated using surface tension, fluorescence probe, dynamic light scattering, and microscopy measurements. The adsorption at the air-water interface and aggregation in the aqueous solution depend on the structure of both hydrophilic head-groups and hydrophobic tails. Spherical vesicles were observed in the aqueous solutions of glycylglycine derivatives, whereas short tubular aggregates were found in that of corresponding glycylglycylglycine products. Intermolecular hydrogen-bonding interaction between the amide head-groups might be responsible for the different self-assembly behavior and microstructure of N-acyl oligopeptide surfactants in the aqueous solution.