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.

Synthesis of homochiral tris-indanyl molecular rods.

Homochiral tris-indanyl molecular rods designed for supramolecular surface self-assembly were synthesized. The chiral indanol moiety was constructed via a Ti-mediated alkyne trimerization. Further manipulations resulted in a homochiral indanol monomer. This was employed as the precursor for successive Sonogashira and Ohira-Bestman reactions towards the homochiral tris-indanyl molecular rods. The molecular rods will be applied for scanning tunnelling microscopy studies of their surface self-assembly and chirality.