Peptide-mediated synthesis of gold nanoparticles: effects of peptide sequence and nature of binding on physicochemical properties

Biomimetic nanotechnologies that use peptides to guide the growth and assembly of nanostructures offer new avenues for the creation of functional nanomaterials and manipulation of their physicochemical properties. However, the impacts of peptide sequence and binding motif upon the surface characteristics and physicochemical properties of nanoparticles remain poorly understood. The configurations of the biomolecules are expected to be extremely important for directing the synthesis and achieving desired material functionality, and these binding motifs will vary with the peptide sequence. Here, we have prepared a series of Au nanoparticles capped with a variety of materials-directing peptides with known affinity for metal surfaces. These nanomaterials were characterized by UV-vis and circular dichroism spectroscopies, transmission electron microscopy, and ζ-potential measurement. Then their catalytic activity for 4-nitrophenol reduction was analyzed. The results indicate that substantially different Au-peptide interfaces are generated using different peptide sequences, even when these sequences have similar binding affinity. This is consistent with recent work showing that Au-peptide binding affinity can have varying entropic and enthalpic contributions, with enthalpically- and entropically-driven binders exhibiting quite different ensembles of configurations on the Au surface. The catalytic activity, as reflected by the measured activation energy, did not correlate with the particle size or with the binding affinity of the peptides, suggesting that the reactivity of these materials is governed by the more subtle details of the conformation of the bound peptide and on the nanoparticle surface reconstruction as dictated by the peptide structure. Such variations in both nanoparticle surface reconstruction and peptide configuration could potentially be used to program specific functionality into the peptide-capped nanomaterials.