Surface active properties of amphiphilic sequential isopeptides: Comparison between α-helical and β-sheet conformations

Poly(Leu–Lys–Lys–Leu) and poly(Leu–Lys) are sequential amphiphilic peptide isomers that adopt respectively an α-helical conformation and a β-sheet structure in saline solutions and at the air/water interface. The surface active properties of LKKL and LK sequential isopeptides containing 16, 20, and n residues have been compared in order to evaluate the contributions of the α-helical and β-sheet conformations. Both have a natural tendency to spread at the surface of a saline solution and the values of the equilibrium spreading pressure πe lie in the same range. When dissolved in a saline solution, α-helical peptides diffuse faster and adsorb faster at the interface than the β-sheet isomers. From the compression isotherms of LKKL and LK peptide monolayers it is possible to extract parameters that characterize the behavior of α-helical and β-sheet conformations: β-sheet peptide monolayers are more stable and less compressible than the monolayers formed with the α-helical isomers. The LK peptides differ also by their high degree of self-association at the air/water interface. © 1999 John Wiley & Sons, Inc. Biopoly 49: 415–423, 1999