Assembly of Multiblock Peptoids into Highly Crystalline Nanosheets

Two-dimensional (2D) nanomaterial provides a promising structural platform for precisely arranging functional molecular or supramolecular motifs and integrating them into functional materials for applications such as biomedicine, energy storage, and catalysis.^{1, 2} In nature, sequence-defined biomolecules can incorporate various functional motifs and assemble into hierarchical structures, including 2D protein assemblies.³ Inspired by these natural systems, various de novo proteins and peptides have been designed and exploited as building blocks for the bio-inspired synthesis of 2D nanomaterials.^{1, 4, 5} However, due to the complex folding of protein and peptide backbones, programmable control over the synthesis and function of such high-information content 2D nanomaterials remains a long-standing challenge.

Peptoid (N-substituted glycine) is one of the well-developed peptidomimetics that exhibits peptide- and protein-like high side-chain diversity while lacking hydrogen bond donors, which enables the tuning of peptoid-peptoid interactions through side-chain chemistry. By taking such structural advantages, a variety of amphiphilic peptoids have been designed and assembled into crystalline nanomaterials, including ultrathin 2D nanomaterials.^6-8 In this work, we designed and synthesized a series of tetra-, hexa- and octablock amphiphilic peptoids with the intention of exploiting the intramolecular folding of peptoid backbones to assemble crystalline nanomaterials. We demonstrated the assembly of these multiblock sequences into highly crystalline 2D nanomaterials, including Janus nanosheets assembled from a tetrablock sequence with two different polar domains. Structural characterizations of these nanosheets revealed that they exhibited a highly ordered molecular packing similar to our previously reported crystalline nanomaterials.^{6, 7} A combination of XRD, AFM and TEM results suggest the intramolecular folding of the peptoid backbone drives the formation of crystalline nanosheets with a high flexibility in tuning surface chemistry. By tuning the surface chemistry of these nanosheets, we further demonstrated their application in surface-templated nanocrystal formation and their covalent attachment of two different nanoparticles (e.g., gold and silica nanoparticles). Given that various side chain groups could be introduced in these multiblock assembling sequences, we expect nanosheets assembled from these multiblock peptoids would provide a new platform for developing functional materials.

References:
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