Self-Assembly of Homo Phenylalanine Oligopeptides: Role of Oligopeptide Chain Length

The self-assembly of phenylalanine (F)-based peptides is a critical area of research with potential implications for the development of advanced biomaterials and technologies. Previous studies indicate that homo-oligopeptides with F-X residues (X = 1 to 6) can self-assemble into diverse nano-microstructures, but the role of oligopeptide chain length on this process remains unclear. This review investigates the role of F-X chain length on self-assembly processes and morphologies, considering the effect of incubation conditions and the capping group at the N and/or C terminals. Morphologies, such as fibrils or tubes, are typical structures that result from the self-assembly of F-X oligopeptides, especially, with an even number of residues. When one or two termini of the F-X oligopeptide are capped, the tendency to form such structures is altered. Highly aromatic F-X oligopeptides display a wide range of morphologies due to hydrophobic cores created by stacked aromatic groups leading to slow formation of poor aggregates without well-defined morphologies. The terminal charges and capping groups on the oligopeptide backbone affect the atomic-level structure of self-assembled F-Xs (X > 1) by driving parallel or antiparallel β-strand associations between F-X monomers. We conclude that oligopeptide chain length plays a critical role in the self-assembly process of F-based peptides and that shorter chains may lead to the formation of more stable and ordered structures. Besides chain length, several other factors influence the structures, including solvent type, cosolvent properties (polarity and volatility), oligopeptide concentrations, and temperature. A significant challenge in investigating self-assembly processes is the lack of a solvent that promotes self-assembly under identical incubation conditions due to solubility variations among F-X oligopeptides. Consequently, additional experimental and mathematical studies are required to examine the self-assembly of F-X oligopeptides under the same incubation conditions (solvent type, cosolvent, peptide concentration, pH, and temperature) to produce viable F-based materials with potential applications in advanced biomaterials and technologies.