Artificial Oligopeptide Scaffolds for Stoichiometric Metal Binding

Two artificial peptides with pendant pyridine or bipyridine ligands have been synthesized and incorporated into oligomeric strands that are analogous to peptide nucleic acid. Spectrophotometric titrations with Cu2+ and Fe2+ show that the oligomers bind stoichiometric quantities of transition metals based on the number of pendant ligands. The identities of the titration products are confirmed by high resolution mass spectrometry. In the case of the bipyridine tripeptides, the titration stoichiometry and mass spectra indicate that the metal ions form interstrand cross-links between two oligopeptides, creating duplex structures linked exclusively by metal ions. Calculated molecular structures of the metalated oligopeptides and duplexes indicate that the peptide backbone acts as a scaffold for the directed assembly of metal ions. Electron paramagnetic resonance spectroscopy of the Cu-containing molecules have varying degrees of electronic interaction based on their charge and supramolecular structure. Cyclic voltammetry of the Fe2+- and Cu2+- linked bpy oligopeptide duplexes shows that they possess unique electrochemical signatures based on the redox reactivity of the metal complex.