Two-Dimensional Coordination Networks from Cyclic Dipeptides.

Peptide-based biomimetic nanostructures and metal-organic coordination networks on surfaces are two promising classes of hybrid materials which have been explored recently. However, despite the great versatility and structural variability of natural and synthetic peptides, the two directions have so far not been merged in fabrication of metal-organic coordination networks using peptides as building blocks. Here we demonstrate that cyclic peptides can be used as ligands to form highly ordered, two-dimensional, peptide-based metal-organic coordination networks. The networks are formed on a Au(111) surface through coadsorption of cyclic dialanine with Cu-adatoms under Ultra-High Vacuum (UHV) conditions. Scanning Tunneling Microscopy (STM) in combination with X-ray Photoelectron spectroscopy (XPS) has been utilized to characterize the network structures at submolecular resolution and expound the chemical changes involved in network coordination. The networks involve a motif of three cyclic dialanine molecules coordinating to a central Cu-adatom. Interestingly the networks expose pores functionalized by the side chain of the cyclic peptide, suggesting a general method to form functionalized porous metal-organic networks on surfaces.