|Ph.D Student||Tigger Hagar|
|Subject||Self-Assembly and Metal NPs Mediated by|
|Department||Department of Chemistry||Supervisor||Professor Galia Maayan|
|Full Thesis text|
Assemblies of metal nanoparticles (NPs) have been broadly used for the construction of materials with distinct spectroscopic properties towards sensing applications. On the other hand, well-dispersed NPs are exploit for applications in catalysis and medicine. Biopolymers or biomimetic oligomers can serve both as efficient stabilizers of NPs and as useful aggregation mediators that can lead to assemblies with unique properties. Controlling aggregation processes, however, is still challenging and often relies on trial and error rather than on defined thumb rules.
Herein we developed specific guidelines for the controlled aggregation of Ag(0) NPs, which was not explores widely before, due to the unstable character of Ag(0) NPs. All our experiments were done at room temperature, in water, near neutral pH and without any additives. We used short peptide mimics, N-substituted glycine oligomers called peptoids, as aggregation mediators, and investigate the influence of sequences variations on the NPs assembly. Spectroscopic and electron microscopy data revealed that both the length of the peptoids and their sequences effect the NPs aggregation. Thus, we demonstrate that we can control both the degree of aggregation and the aggregates sizes by tuning these properties. Specifically we show that longer peptoid sequences as well as sequences consisting of aromatic side chains are required for the formation of uniform quasi-spherical NPs assemblies in an average size of 70 nm, while a short hydrophilic sequence could stabilize well-dispersed Ag(0) NPs. Moreover, we showed that by controlling the degree of Ag(0) NPs aggregation, we can also achieve control over the catalytic activity of Ag(0) NPs in the reduction of 4-nitrophenol to 4-aminophenol.
In addition, we demonstrated that we could control the morphology of the aggregates by tuning the length, monomer identity and capping ligand of the peptoid. Specifically, we show that a peptoid heptamer containing the capping ligand 1,10-phenanatrolin, which is directly bound in its N-terminus, and has aromatic side chains in the other positions, is required for the formation of uniform spherical NP-assemblies. In contrast, the same heptamer peptoid, bearing the capping ligand 2,2'-bipyridine, which is attached via a flexible linker at its N-terminus, promoted the formation of nanochain-like NP assemblies. The utilization of 1,4-butanedithiol or pyridine derivatives as capping ligands resulted in partial aggregation and/or heterogeneous morphology.
These results open up various opportunists for exploring new morphologies of NP-assemblies simply by tuning the capping ligands incorporated within peptidomimetic oligomers, and for constructing unique biomimetic functional materials based on controllable assembly of Ag(0) NPs.