Synthesis and surface activity properties of hydrophobic/hydrophilic peptides

In order to explore the ability of amphiphilic peptides to behave as surface-active agents with emulsifying properties, several short peptides of leucine and glutamine were synthesized with different periodicity, length and hydrophobic characteristics. The stepwise liquid-phase procedure using the N-hydroxysuccinimide ester was deployed in all chain-lengthening steps, and the same procedure was also used subsequently to modify some of the products by introducing a lipophilic moiety such as a palmitoyl residue. The surface-active properties of these products were evaluated by measuring the variation of surface (gamma s) and interfacial (gamma i) tensions and the formation of micelles as a function of concentration in aqueous solution. The alternating sequence (Leu-Gln)n showed good surface activity behaviour, similar to those of recognized surfactants, albeit with no emulsifying function. More hydrophobic compounds, such as lipopeptides, lowered the surface tension of water at concentrations markedly below those usually observed for classical surfactants, and emulsifying properties were observed in all the peptides substituted with lipophilic moieties.