Chemistry, structural insight and applications of β-sheet forming lipopeptides

Abstract

The research described in this thesis aimed to synthesize and investigate the physical properties of a new series of amphiphilic lipopeptides, ALPs. These molecules were composed of an amphiphilic oligopeptide domain, (Leu-Glu)n , interlinked by a succinyl moiety to the phospholipid 1,2-Dioleoyl-sn-Glycero-3-Phosphoethanolamine (DOPE). The ALPs were designed to form supramolecular assemblies composed of β-sheet arrays decorated by hydrophobic lipid tails. First the ALPs were investigated for the ability to form well-ordered monolayers at the air-water interface. The sequential order of hydrophobic and hydrophilic amino acids was chosen to induce the generation of a β-sheet secondary structure at the air-water interface. The peptide backbones in the β-sheet conformation were expected to lay with their long molecular axes parallel to the interface so that the hydrophobic side groups pointed towards the air and the hydrophilic side chains were distributed regularly on the water interface. Because of the hybrid nature of the ALPs, the possibility that the phospholipid tails would interfere with the β-sheet organization was considered. The proper length of the peptide domain, necessary to generate the β-sheet organization, was therefore investigated and three ALPs were prepared, each exhibiting a different length of the peptide part, (Leu-Glu)2-,(Leu-Glu)3- and (Leu-Glu)4, termed tetra-, hexa- and octa-ALP, respectively. Subsequently, the application of the ALP monolayers for the nucleation of calcium carbonate was shown. Next, the self-assembly properties of the ALPs upon dispersion in aqueous solutions were investigated. The preparation of lipid vesicles decorated by β-sheet peptides was rather difficult. Therefore a new synthetic approach was investigated to functionalize pre-formed liposome surfaces by peptides based on copper(I)-mediated [3+2] azide-alkyne cycloaddition (“click” chemistry).​​​​​​​