Self-assembly of l-phenylalanine amino acid: Electrostatic induced hindrance of fibril formation

Abstract

Nanostructure morphology originating from the self-assembly of molecules has attracted substantial attention due to its role in toxic amyloid fibril formation and immense potential in the design and fabrication of novel biomaterials. This study presents the role of intermolecular electrostatic interaction on the self-assembly process of l-phenylalanine (L-Phe) amino acid. We have employed attenuated total reflection Fourier transform infrared spectroscopy to probe the existence of different ionization states of the amino acid in various pH aqueous solutions. The self-assembly process of L-Phe in the aqueous phase is explored by using circular dichroism absorption and nuclear magnetic resonance spectroscopic tools. The observed spectral features have shown the signature of higher order structures and possible perturbation in the π-π stacking aromatic interactions for the cationic and anionic states of the amino acid. Scanning electron microscopy is used to probe the self-assembled morphology of the L-Phe amino acid dried samples prepared from the same pH aqueous solutions. We find that for the case of zwitterionic states the self-assembly nanostructures are dominated by the presence of fibrillar morphology, however interestingly for cationic and anionic states the morphology is dominated by the presence of flakes. Our finding demonstrates the potential influence of intermolecular electrostatic interaction over the aromatic π-π stacking interaction in hindering the fibril formation.