Compact Peptoid Molecular Brushes for Nanoparticle Stabilization

Abstract

Controlling the interfaces and interactions of colloidal nanoparticles (NPs) via tethered molecular moieties is crucial for NP applications in engineered nanomaterials, optics, catalysis, and nanomedicine. Despite a broad range of molecular types explored, there is a need for a flexible approach to rationally vary the chemistry and structure of these interfacial molecules for controlling NP stability in diverse environments, while maintaining a small size of the NP molecular shell. Here, we demonstrate that low-molecular-weight, bifunctional comb-shaped, and sequence-defined peptoids can effectively stabilize gold NPs (AuNPs). The generality of this robust functionalization strategy was also demonstrated by coating of silver, platinum, and iron oxide NPs with designed peptoids. Each peptoid (PE) is designed with varied arrangements of a multivalent AuNP-binding domain and a solvation domain consisting of oligo-ethylene glycol (EG) branches. Among designs, a peptoid (PE5) with a diblock structure is demonstrated to provide a superior nanocolloidal stability in diverse aqueous solutions while forming a compact shell (∼1.5 nm) on the AuNP surface. We demonstrate by experiments and molecular dynamics simulations that PE5-coated AuNPs (PE5/AuNPs) are stable in select organic solvents owing to the strong PE5 (amine)–Au binding and solubility of the oligo-EG motifs. At the vapor–aqueous interface, we show that PE5/AuNPs remain stable and can self-assemble into ordered 2D lattices. The NP films exhibit strong near-field plasmonic coupling when transferred to solid substrates.

A Field Guide to Optimizing Peptoid Synthesis

“…Designing peptoids for various biomaterials applications requires synthetic versatility, which has remained a challenge in solution-phase peptoid synthesis. Increasing the variety of accessible side chains provides opportunities to explore the influence of functional groups on different application-relevant properties such as self-assembly, biological activity, and biorecognition. − Most solution-phase peptoid research has focused on linear alkyl side chains because the polymerization rate has been shown to be affected by side chain length and bulkiness. Density functional theory (DFT) calculations have shown that steric hindrance of beta-branched alkyl side chains contributes to reduced rates of polymerization and van der Waals interactions lead to aggregation for linear and gamma-branched side chains .…”

Interfacial Microstructure of Neutral and Charged Polymer Brushes: A Density Functional Theory Study

“…In the presence of an external potential, the free energy of the system brush is expressed as (5) where P and C are the self-consistent parameters determined by the physical constraints of the grafted polymer chain and counterions, respectively.…”

“…Polymer brushes (PBs) are assembled by anchoring polymeric chains onto a surface, triggering an increasing interest due to the unique chemical and structural characteristics of polymeric chains. 1-2 So far, PBs have made significant contributions to a broad range of traditional and emerging applications such as biological lubrication 3 , thermal and electrical stimuli-responsive surface 4 , colloidal stabilization and surface protection 5 , novel substrate modification, 6-7 biosensing and nanomaterial synthesis, etc. 8 These applications are highly dependent on the interfacial microstructure of PBs and straightforwardly benefited from its precise tuning.…”

Photo-Cross-Linked Polymeric Dispersants of Comb-Shaped Benzophenone-Containing Poly(ether amine)

“…Significant efforts have been dedicated to surface functionalization of NPs in order to prevent their aggregation, which can be achieved through two main approaches: (1) chemical modification, − which includes both “graft to” and “graft from” methods, and (2) physical adsorption of dispersants. − These studies have provided both theoretical and experimental foundations for modifying effectively surface structure of NPs to prepare stable dispersion systems. In the case of pigments, introducing reactive groups on the surface and utilizing sequence condensation reactive has led to stronger stability of pigment suspensions .…”