Peptide-Induced Formation of Crystalline Sn6O4(OH)4 Nanoparticles under Ambient Conditions

The short peptides that specifically bind to SnO2 nanoparticles (NPs) were selected by using a phage display method. After the fourth round selection, ten kinds of amino acid sequences were identified, and it was revealed that affinities of the obtained phages for SnO2 NPs were relatively higher than that of the unselected library phages. The identified peptide sequences showed that amino acids having a hydroxy group and hydrophobic amino acids were enriched in the selection process. Binding constants (K-a) of the chemically synthesized heptapeptides having the identified sequences were quantitatively estimated. The pTO-7 peptide (Ser-Ser-Ile-Leu-Arg-Phe-Pro) showed the greatest K-a value (5.80 x 10(5) M-1 at 25 degrees C) among the investigated peptides, and also showed binding specificity to SnO2. The SnO2-recognizing peptides functioned as nanostructure stabilizer during pH-dependent preparation of water-insoluble tin-based compound (Sn6O4(OH)(4)) at room temperature. These effects as stabilizers to disperse nanostructures in water phase were greater than that of a general purpose stabilizer poly(vinylpyrrolidone). Dynamic light scattering and transmission electron microscope analyses revealed that the formed structures in the presence of the pTO-7 peptide were squarish NPs with an approximately 60 nm diameter, and wide-angle powder X-ray diffraction analyses suggested that its crystallinity was increased by existence of the peptide.