Preparation of Hierarchically Assembled Silver Nanostructures based on the Morphologies of Crystalline Peptide-Silver(I) Complexes.

The preparation of a hierarchically assembled Ag nanostructures based on a nanocrystalline assembly was demonstrated using an Ag(I) complex of a dipeptide (AspDap). By heating under N2 gas, a spherical assembly of a nanocrystalline dipeptide-Ag(I) complex (diameter 4-5 µm), which has a morphology similar to the assembled structure of the dipeptide, was transformed to an assembly of Ag nanostructures, where the micrometre-order crystalline morphology was maintained. In addition, detailed scanning electron microscopy studies revealed that Ag nanoparticles (diameter ca. 10 nm) were formed on the surface of the Ag nanostructure. When the Ag(I) ions were reduced to Ag(0), this phenomenon exhibited surface dependence due to the anisotropic two-dimensional Ag(I) arrangement in the crystals. Thermogravimetric measurements and X-ray photoelectron spectroscopy revealed that the reduction proceeds in a stepwise manner around 200-250 °C, together with the removal of primary and secondary carboxylic groups in the dipeptide. Comparison with the heating process of the crystalline Ag(I) complex of ß-alanine indicated that stepwise reduction is key for maintaining the original micrometre-order morphology.

Construction of hybrid films of silver nanoparticles and polypyridine ruthenium complexes on substrates.

Hybrid films of functional molecules and metal nanoparticles have been considered to be novel photo-functional devices. Here we have successfully constructed hybrid films of silver nanoparticles and ruthenium polypyridine derivatives on substrates. In order to hybridise them on a surface, a self-assembled monolayer method via chemical bond formation and electro-reductive polymerisation (thick layers) via physical attachment have been employed. These methods have the advantage of convenient and reproducible fabrication of complicated hybrid films. Furthermore, it has been clarified that these hybrid films show unique photo-functional behaviours, such as enhanced photocurrent generation.