Spontaneous Alignment of Self-Assembled Cationic and Amphiphilic β-Sheet Peptides

Aligned peptide assemblies are of interest for both fundamental understanding of biological systems as well as development of novel biomaterials. Herein, Pro-Lys-(Phe-Lys)₅-Pro (PFK), a cationic and amphiphilic β-sheet synthetic peptide that self-assembles into fibrils, capable of undergoing spontaneous isotropic to nematic phase transition, that intrinsically aligns in solution, is presented. Upon dissolution PFK forms isotropically dispersed fibrils due to delicate balance between attractive H bonds and hydrophobic interactions to electrostatic repulsive forces. The transition from isotropic to nematic phase alignment occurring over a period of several days is monitored in situ by both small-angle X-ray scattering and cryogenic transmission electron microscopy. The degree of alignment and the time required to achieve a complete isotropic–nematic phase transition of PFK fibrils in aqueous solution is found to be concentration dependent as predicted by Onsager's excluded volume theory. Remarkably, PFK nematic phases remain aligned over the course of several months without the application of any external stimuli. Aligned PFK gels can be formed by mild shearing through a salty medium. This system provides a novel route for producing nanoscale aligned materials for potential biomedical applications.