Biomimetic Control of Sequence-Defined Peptoids Over Ag Nanocrystal Formation and Anisotropic Self-Assembly

Controlling the stability and assembly of plasmonic nanoparticles through biomimetic strategies has significant potential for both advancing the fundamental science of biomimetic synthesis and developing functional applications. However, achieving such control remains a great challenge due to a lack of readily programable ligands and limited mechanistic understanding. Here we demonstrate that sequence-defined peptoids, which serve as capping and structure-directing agents, can drive cooperative formation and self-assembly of ~ 2-3 nm Ag nanocrystals (NCs) into nanoribbons in a template-free manner through a two-step process comprised of i) formation of Ag NCs with a ~1.8 nm thick surface-adsorbed peptoid layer, followed by ii) peptoid-driven anisotropic assembly of the Ag NCs. By examining the effects of peptoid side chain chemistry and varying reaction conditions, and comparing the results to computational simulations, we conclude that: 1) the stability of Ag NCs is attributable to the stronger interactions with peptoids than peptoid-peptoid interactions, and 2) self-assembly is initiated by the reorganization of the hydrophobic tails of peptoid ligands to achieve the typical pi-pi stacking seen in 2D sheets formed from similar peptoids in the absence of Ag NCs. The self-assembly behavior of peptoid-stabilized NCs can be rationalized based on the simulation results, which predict that attractive hydrophobic inter-peptoid interactions drive the approach of neighboring Ag NCs and the subsequent reorganization of the peptoids ligands. This work provides insight into how peptoids can be programmed to control both inorganic nanomaterials formation and self-assembly into hierarchical nanostructures, offering a new strategy for the design and synthesis of functional materials.