Cu^II cross-linked antiparallel dipeptide duplexes using heterofunctional ligand-substituted aminoethylglycine

Two artificial dipeptides containing both a pendant monodentate (pyridine (py)) and tridentate (terpyridine (tpy) or phenyl terpyridine (tpy)) ligand on an aminoethylglycine (aeg) backbone have been synthesized. These oligopeptides are fully characterized by one and two-dimensional NMR spectroscopy, mass spectrometry, and elemental analysis. The ligands were chosen because they coordinate Cu²⁺ to form [Cu(py)(tpy)]²⁺ complexes; when bound to the dipeptide scaffold, Cu²⁺ chelation cross-links the strands to form double-stranded duplex structures with an antiparallel arrangement. Using spectrophotometric titrations, we observe coordination of one Cu²⁺ metal per dipeptide strand. Mass spectrometry, NMR spectroscopy, vapor pressure osmometry, and HPLC confirm that the resulting structures are the dipeptide duplex cross-linked by two metal centers.