Encapsulation of pyrene within self-assembled peptide amphiphile nanofibers

Certain peptide amphiphiles (PAs) in aqueous media are known to form high-aspect-ratio cylindrical nanofibers with hydrophobic cores. Using cholesterol or palmitic acid as the hydrophobe and the biological adhesion epitope RGDS as the hydrophilic segment, we studied the encapsulation of pyrene, a small hydrophobic molecule, within the cores of the self-assembling PA nanofibers. Circular dichroism (CD), transmission electron microscopy (TEM) and fluorescence were used to characterize formation of the supramolecular structures. Pyrene excimer formation observed by fluorescence demonstrated the encapsulation and aggregation of pyrene within the hydrophobic cores. In addition, peptide amphiphiles covalently functionalized with pyrene linked to the hydrophobic portion of the molecule exhibited excimer formation upon self-assembly into nanofibers. Interestingly excimer formation was not observed in similar molecules that formed spherical aggregates rather than cylindrical nanofibers.