Electrochemical and Surface Study of Ferrocenoyl Oligopeptides

The syntheses and characterizations of several symmetric ferrocenoyl (Fc)−peptide cystamines ([Fc-Gly-CSA]2, [Fc-Ala-CSA]2, [Fc-Ala-Ala,CSA]2, [Fc-Ala-Phe-CSA]2, together with an unsymmetric Fc-Ala-Ala-CSA-Ala-Fc) is reported. All systems show intermolecular hydrogen bonding in solution. In the solid-state, [Fc-Gly-CSA]2 and [Fc-Ala-CSA]2 exhibit strong intermolecular H-bonding, as expected from solution studies, forming a network of β-helical supramolecular structures. Monolayers of the Fc−peptide cystamines produced structures that show a uniform thickness of 7(2) Å but are not well ordered, leaving about 10−15% of the Au surface exposed as determined by Cu underpotential deposition. E0‘ values of all the monolayers are in the range of 460−510 mV. Monolayer dilution with hexanethiol caused an anodic redox shift of approximately 20 mV and a slight increase in the electron-transfer kinetics.