In Situ Synthesis of Shape-Selective Gold Nanocrystals Using Oligopeptide Template: Effect of Various Reaction Parameters

An oligopeptide with a free amino group at the N-terminus and a redox active tryptophan residue at the C-terminus was used to synthesize gold nanocrystals of different shapes. The concentration ratio of peptide to HAuCl₄ has a significant effect on the shape of the formed nanocrystals and the polyhedral gold nanocrystals are mainly formed at higher such ratio. The effect of medium pH and reaction temperature on the shape of the formed gold nanocrystals has also been investigated. However, an oligopeptide with blocked amino group with tert-butyloxycarbonyl group resulted only spherical gold nanocrystals along with some aggregated structures. A probable mechanism for the formation of polyhedral gold nanocrystals has been described, which indicate the presence of multiple anchoring sites in the peptide molecules is mainly responsible for this type of crystal growth. The formed nanocrystals were well characterized by various experimental techniques like, UV-visible spectroscopy, transmission electron microscopy, and X-ray diffraction.