Halogen bonding as a key interaction in the self-assembly of iodinated diphenylalanine peptides

The diphenylalanine peptide FF (H2N-Phe-Phe-COOH) is a simple building-block that has been extensively studied for multiple purposes. Among the many possible mutations finalized to tailor specific functions and properties of FF-based materials, halogenation was marginally considered despite the huge changes it confers to molecular self-assembly. Here, we report a detailed study on the role of halogenation, specifically iodination, in the aggregation behavior of iodine-modified FF dipeptides. Single-crystal X-ray structures of mono-iodinated-F(I)F-and bis-iodinated-F(I)F(I)-diphenylalanine reveal that halogen atoms exert a key role in the packing features of these compounds. Specifically, halogen bonding provides additional stability to the dry interfaces formed by the aromatic rings, providing a contribution in the solid-state packing of these dipeptides. The structural evidence of halogen bonding as crucial noncovalent interaction confirms the great potential of halogenation as supramolecular tool for peptide-based systems.