Hybrid peptide-PNA monomers as building blocks for the fabrication of supramolecular aggregates

Advantages like biocompatibility, biodegradability and tunability allowed the exploitation of peptides and peptidomimetics as versatile therapeutic or diagnostic agents. Because of their selectivity towards transmembrane receptors or cell membranes, peptides have also been identified as suitable molecules able to deliver in vivo macromolecules, proteins or nucleic acids. However, after the identification of the homodimer diphenylalanine (FF) as an aggregative motif inside the Aβ_1–42 polypeptide, short and ultrashort peptides have been studied as building blocks for the fabrication of supramolecular, ordered nanostructures for applications in biotechnological, biomedical and industrial fields. In this perspective, many hybrid molecules that combine FF with other chemical entities have been synthesized and characterized. Two novel hybrid derivatives (tFaF and cFgF), in which the FF homodimer is alternated with the peptide-nucleic acid (PNA) heterodimer “g-c” (guanine-cytosine) or “a-t” (adenine-thymine) and their dimeric forms (tFaF)₂ and (cFgF)₂ were synthesized. The structural characterization performed by circular dichroism (CD), Fourier transform infrared (FTIR) and fluorescence spectroscopies highlighted the capability of all the FF-PNA derivatives to self-assemble into β-sheet structures. As a consequence of this supramolecular organization, the resulting aggregates also exhibit optoelectronic properties already reported for other similar nanostructures. This photoemissive behavior is promising for their potential applications in bioimaging.