Electric-field-enhanced oriented cobalt coordinated peptide monolayer and its electrochemical properties.

The monolayer composed of cobalt coordinated peptides having lipoic acid at the amino terminals was fabricated on gold substrate by a self-assembly method under the electric field. For comparison, the self-assembled peptide monolayer was also prepared without applying a voltage. A leucine-rich hexadecapeptide, Leu(2)HisLeu(6)HisLeu(6), was chosen as the cobalt coordinated peptide. Histidines, His, were introduced as metal ligands for cobalt to the sequential peptide. The complexation between the cobalt and imidazole groups of His residues formed a stable α-helical peptide bundle, which oriented perpendicularly to the substrate surface. In the case of the self-assembled peptide monolayer (SAM), which was fabricated under the electric field, the peptide macro-dipole moments aligned unidirectionally along to the direction of the electric field, and the cobalt complexes were fixed in the monolayer to form the ordered arrangement. On the other hand, the SAM prepared without applying the voltage formed the mixture of parallel and antiparallel packing owing to the dipole-dipole interaction. As the result, the efficient non-linear electron flow through the SAM, which was fabricated under the electric field, was achieved by the regular alignment of the peptide macro-dipole moment and the cobalt complexes. This result implied that the self-assembly under the electric field is an efficient method to obtain stable oriented α-helical peptide monolayers. This method may be useful for the fabrication of the nano-devices capable of transferring information.