Redox behavior of phenyl-terpyridine-substituted artificial oligopeptides cross-linked by Co and Fe

This work presents the synthesis and characterization of metalated oligopeptide duplex assemblies composed of artificial oligopeptides bearing tethered phenyl terpyridine ligands that are coordinated to Co(II) and Fe(II) ions. The metals cross-link the oligopeptide strands, forming duplex structures. UV-vis spectrophotometric titrations that monitor the absorbance of the metal complexes' characteristic MLCT bands demonstrate stoichiometric metal chelation. Anodic peaks in the cyclic voltammograms of these molecules are consistent with one-electron oxidative reactions without strong coupling between the metal complexes. In separate chronocoulometry measurements, the diffusion coefficients of the metal complexes decrease with increasing oligopeptide length, suggesting the primary products are metal-linked oligopeptide duplex assemblies. Larger metalated oligopeptides adsorb to electrode surfaces during cyclic voltammetry and yield irreversibly adsorbed electroactive films with thicknesses that depend on the number of voltage cycles. Electrochemical and spectroelectrochemical investigations of the films on Pt and ITO electrodes show that the electron transfers in the adsorbed films are chemically reversible but are kinetically quasi-reversible.