Fabrication of oriented helical polypeptide brushes on gold

An α-helical poly(γ-benzyl-L-glutamate) labeled at its N-terminus with disulfide moieties, PBLG-SS, was synthesized to examine the self-assembling property of helical rods onto a gold surface. Adsorption processes and resultant helical PBLG-SS monolayers on gold were characterized by quartz crystal microbalance measurements and barrier capability toward [Fe(CN)₆]^3-/4- in aqueous solution. When PBLG-SS was dissolved in CHCl₃, a densely packed monolayer was formed on the gold surface and the helical rods aligned in antiparallel manner based on the helix-macrodipole interaction. In contrast, when PBLG-SS was dissolved in DMSO, a loosely packed monolayer was formed and the helix-macrodipole was directed in the same sense. The electric field at the electrode/electrolyte interface was used to affect helix orientation. As a result, predominant chemisorption of PBLG-SS molecule was present on the negative gold electrode. This is suggestive of parallel alignment of helix-macrodipole on the basis of electric field effects.