Supramolecular Chemistry of Hybrid Cyclophane-Cyclopeptide Receptors

Hybrid cyclophane-cyclopeptide receptors contain an alternating sequence of natural and non-natural aromatic amino acids. They were first described in 1995 by Ishida et al. as receptors for oxoanions in DMSO. Work in my group showed that by structurally varying the subunits along the ring, which in turn allowed controlling the preferred cyclopeptide conformation, cyclopeptide-based receptors could also be obtained for quaternary ammonium ions, ion pairs, amino acids, and carbohydrates. Of particular interest in this context was a cyclic hexapeptide containing proline and 6-aminopicolinic acid subunits, which has the, for a neutral compound, unusual ability to bind anions such as sulfate and halides with high affinity in competing aqueous solvent mixtures and in water. This cyclopeptide therefore allowed investigating important principles of molecular recognition processes in water. In addition, it inspired the development of a family of 1,2,3-triazole-containing cyclic pseudopeptides, one of which exhibited pronounced phosphate affinity, albeit in DMSO. Immobilization of the anion-binding cyclopeptide on the surface of gold nanoparticles finally gave rise to optical probes for sulfate anions in water. In my talk, I will give an overview of the supramolecular chemistry of these cyclopeptides and cyclopseudopeptides, with an emphasis on recent developments.