Two-Dimensional\nCoordination Networks from Cyclic Dipeptides

Abstract

Peptide-based biomimetic nanostructures\nand metal–organic coordination networks on surfaces are two\npromising classes of hybrid materials which have been explored recently.\nHowever, despite the great versatility and structural variability\nof natural and synthetic peptides, the two directions have so far\nnot been merged in fabrication of metal–organic coordination\nnetworks using peptides as building blocks. Here we demonstrate that\ncyclic peptides can be used as ligands to form highly ordered, two-dimensional,\npeptide-based metal–organic coordination networks. The networks\nare formed on a Au(111) surface through coadsorption of cyclic dialanine\nwith Cu-adatoms under Ultra-High Vacuum (UHV) conditions. Scanning\nTunneling Microscopy (STM) in combination with X-ray Photoelectron\nspectroscopy (XPS) has been utilized to characterize the network structures\nat submolecular resolution and expound the chemical changes involved\nin network coordination. The networks involve a motif of three cyclic\ndialanine molecules coordinating to a central Cu-adatom. Interestingly\nthe networks expose pores functionalized by the side chain of the\ncyclic peptide, suggesting a general method to form functionalized\nporous metal–organic networks on surfaces.