Sonication-induced instant fibrillation and fluorescent labeling of tripeptide fibers

Abstract

The peptide Boc-Phe-Acp-Phe-OMe 1 (Acp = ε-aminocaproic acid), containing a core of conformationally flexible achiral amino acids and two termini of L-phenylalanine residues, behaves differently on ultrasound exposure. The ultrasound provides the energy to reset the normal self-assembly pattern and modify the morphology of the peptides from polydisperse nanospheres to an entangled fiber network. The sonication induces instant fibril formation, organogelation in toluene, xylene and 1,2-dichlorobenzene, and crystallization in cyclohexane. X-ray crystallography reveals that the peptide 1 adopts a kink-like conformation and self-associates to form a parallel sheet-like structure through multiple intermolecular hydrogen bonds, where the phenyl groups are on the surface of the sheet like hot spots. Field emission scanning electron microscopy (FE-SEM) of the peptide xerogel reveals the sonication-induced nanofibrillar morphology. Further, the sonication-induced fibril formation technique has been used for supramolecular fluorescent labeling of the peptide nanofibers with organic dyes, such as 2,3,6,7-tetrabromonaphthalene diimide and coumarin, and the capture and slow-release of the drug carbamazepine.