Structure–Rheology Relationship in Nanosheet-Forming Peptoid Monolayers

Abstract

Peptoid nanosheets are novel protein-mimetic materials that form from the supramolecular assembly of sequence-defined peptoid polymers. The component polymer chains organize themselves via a unique mechanism at the air-water interface, in which the collapse of a compressed peptoid monolayer results in free-floating, bilayer nanosheets. To impart functionality into these bilayer materials, structural engineering of the nanosheet-forming peptoid strand is necessary. We previously synthesized a series of peptoid analogues with modifications to the hydrophobic core in order to probe the nanosheet tolerance to different packing interactions. Although many substitutions were well-tolerated, routine surface pressure measurements and monolayer collapse isotherms were insufficient to explain which molecular processes contributed to the ability or inability of these peptoid analogues to form nanosheets. Here, we show that surface dilational rheology measurements of assembled peptoid monolayers at the air-water interface provide great insight into their nanosheet-forming ability. We find that a key property required for nanosheet formation is the ability to assemble into a solidlike monolayer in which the residence time of the peptoid within the monolayer is very long and does not exchange rapidly with the subphase. These collapse-competent monolayers typically have a characteristic time of diffusion-exchange values, τ, of >5000 s. Thus, rheological measurements provide an efficient method for assessing the nanosheet-forming ability of peptoid analogues. Results from these studies can be used to guide the rational design of peptoids for assembly into functional nanosheets.

Design and preparation of organic nanomaterials using self‐assembled peptoids

“…Further modifications of the standard B28 chemical structure were adopted to optimize the conditions of the nanosheet formation, using shorter peptoid strands or different apolar residues, keeping the block polar domains (composed of Nae and Nce residues) constant . Twelve monomer long peptoids were able to successfully form nanosheets, only increasing the hydrophobicity of the apolar domains, by alternating Nbpe and Npe or Nfpe ( N ‐2‐(4‐[trifluoromethyl]‐ phenylethyl)glycine) and Npe residues.…”

Peptoids as tools and sensors

“…Full details of peptoid nanosheet formation, functionalisation and some applications have already been presented . Furthermore, peptoid nanosheets as antibody mimetics has been thoroughly reviewed by Robertson et al …”

Polypeptoid polymers: Synthesis, characterization, and properties

“…As a result of these structural attributes, polypeptoids tend to self-associate or aggregate in solution or at interfaces. [88,119,120] Understanding their supramolecular assemblies in solution or at the interface will be of fundamental importance and will have implications for practical uses of these polymers in solution-based applications. With advances in synthesis, understanding of how molecular interactions encoded in the N-substituent structures and monomer sequences impact the nanoscale and mesoscale assemblies of polypeptoids will be of significant interest in the rational design of polypeptoid polymers for targeted applications.…”