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 beta-helical supramolecular structures. Monolayers of the Fc-peptide cystamines produced structures that show a uniform thickness of 7(2) Angstrom but are not well ordered, leaving about 10-15% of the Au surface exposed as determined by Cu underpotential deposition. E-0' 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.