Fabrication of a switchable nano-surface composed of acidic and basic block-polypeptides

We describe herein the fabrication of stimuli-responsive switchable nano-surfaces by using acidic and basic block-polypeptides. Two types of diblock-polypeptides, poly(γ-benzyl-l-glutamate)-block-poly(Nɛ-benzyloxycarbonyl(Z)-l-lysine) (PBLG-block-PZLL) and PZLL-block-PBLG, were first prepared by stepwise polymerization of N-carboxy anhydrides (NCAs) of γ-benzyl-l-glutamate and Nɛ-benzyloxycarbonyl-l-lysine from amino groups immobilized on gold surface. Fourier transfer infrared and X-ray photoelectron spectroscopies analyses showed that the peptide layers obtained after polymerization of the first monomer, namely Au/PBLG or Au/PZLL, were rich in α-helix, and the average tilt angles of the helices from the surface normal were evaluated to be ca. 70° in both cases. In addition, the block polymerization on gold surface was found to cause a partial conversion of the peptide segments into β-sheet structure as well as an increase in film thickness. Subsequently, ionic diblock-peptides composed of poly(l-glutamic acid) and poly(l-lysine) were successfully prepared by removal of side chain protecting groups on gold surface. The surface properties such as wettability and charge distribution of these diblock-peptide nanofilms were found to be regulated by the conformation and ionized state of the outer peptide layer. These results should provide useful information to construct novel peptide-based nano-surfaces.