Preparation and characterization of polypeptide-stabilized gold nanoparticles.

Helical polypeptides have a highly rigid conformation. In order to control self-assembling structure in nanoscale, the rigidity of the stabilizing molecules, which is working as scaffolds, is highly important. Furthermore, the molecular lengths of polypeptides can be readily controlled by using their unique polymerization methods. In this study, we have used helical polypeptides as the stabilizing reagent of metal nanoparticles. As for rigid helical polypeptides, poly(gamma-benzyl-L-glutamate) (PBLG) was selected, and was synthesized by N-carboxylic acid anhydride (NCA) polymerization. Preparation of helical polypeptide-stabilized gold nanoparticles using a two-phase reduction process from the corresponding metal salts with NaBH4 is therefore introduced. PBLG itself did not have good stabilizing ability for metal nanoparticles and a terminal attaching ligand was indispensable for nanoparticle stabilization and, for this purpose, lipoic acid was selected. It is estimated that lipoic acid functionalized polypeptide molecules were attached perpendicularly to the particle surface by lipoic acid group. The size and structure, as well as assembling will be discussed in this manuscript.