Interfacial rheological properties of cholesteryl-oligopeptide surfactants: Effects of hydrophilic group structure

Abstract

Surfactants derived from natural compounds have a wide variety of molecular structures and exhibit various functions. In the present work, 5 surfactants were synthesized by linking a cholesteryl group to different amino acid/oligopeptides. The enhanced intermolecular van der Waals interactions between the cholesteryl group provided a strong driving force for the ordered assembly of surfactants at interface. The interfacial properties of these surfactants were also influenced significantly by the number and type of amino acids in the oligopeptides. As the number of amino acids in the oligopeptides increased, the number of hydrogen bonding sites increased, which in turn enhanced the interfacial activity as well as the intermolecular interactions between the derived surfactants. Meanwhile, because of the synergy of multiple hydrogen bonds and strong van der Waals forces between kalium cholesteryl triglycine (Chol-GGG-K) molecules, the interfacial relaxation processes were greatly inhibited and the interfacial film was less viscoelastic. The functional groups in kalium cholesteryl glycyl-L-valine (Chol-GT-K) and kalium cholesteryl glycyl-L-tyrosine (Chol-GV-K) hindered hydrogen bond formation between the oligopeptides and also slowed the relaxation processes at the interface, which decreased the interfacial viscoelasticity of the Chol-GT-K and Chol-GV-K films. The obtained results provide new insights into the relationships between the molecular structure and interfacial behaviors of cholesteryl-oligopeptide surfactants and provide a framework for surfactant design and further application in the food, pharmaceutical, cosmetic, and material industries.