Structural control of peptide-coated gold nanoparticle assemblies by the conformational transition of surface peptides

Abstract

Gold nanoparticles having peptide chains on the surfaces have been prepared yb ring-opening polymerization of γ-methyl l-glutamate N-carboxyanhydride with fixed amino groups on the nanoparticle surface as an initiator. The number of peptide chains on the surface was adjusted to ca. 2 molecules per gold nanoparticle by controlling the number of fixed amino groups on the surface. The peptide chains on the surface were partially saponified to obtain poly( γ-methyl l-glutamate- co- l-glutamic acid) with 28 mol% of glutamic acid residues. The number-average molecular weight of the peptide was 73,000. We described structural control of the peptide-coated gold nanoparticle assembly by conformational transition of the surface peptides. In deionized water, the peptide chains on the nanoparticle took a random coil conformation, and the individual nanoparticles existed in dispersed globular species. On the other hand, the peptide chains on the nanoparticle took an α-helical conformation in trifluoroethanol. Under this condition, the α-helical peptide chains on distinct gold nanoparticles connected the nanoparticles to form a fibril assembly owing to the dipole–dipole interaction between the surface peptide chains. The morphology of the peptide-coated gold nanoparticle assembly could be controlled by the conformational transition of surface peptides, which was attended by solution composition changes.