Surface active properties of amphiphilic sequential isopeptides: Comparison between alpha-helical and beta-sheet conformations

Poly(Leu-Lys-Lys-Leu) and poly(Leu-Lys) are sequential amphiphilic peptide isomers that adopt respectively an alpha-helical conformation and a beta-sh eet structure in saline solutions and at rite air/water interface. The surf ace active properties of LKKL and LK sequential isopeptides containing 16, 20, and n residues have been compared in order to evaluate the contribution s of the alpha-helical and beta-sheet conformations. Both have a natural te ndency to spread at the surface of a saline solution and the values of the equilibrium spreading pressure pi(e) lie in the same range. When dissolved in a saline solution, alpha-helical peptides diffuse faster and adsorb fast er at the interface than the beta-sheet isomers. From the compression isoth erms of LKKL and LK peptide monolayers it is possible to extract parameters that characterize the behavior of alpha-helical and beta-sheet conformatio ns: beta-sheet peptide monolayers are more stable and less compressible tha n the monolayers formed with the alpha-helical isomers. The LK peptides dif fer also by their high degree of self-association at the air/water interfac e. (C) 1999 John Wiley & Sons, Inc.