Self-Assembly\nof an α‑Helical Peptide into a Crystalline Two-Dimensional\nNanoporous Framework

Abstract

Sequence-specific peptides have been\ndemonstrated to self-assemble into structurally defined nanoscale\nobjects including nanofibers, nanotubes, and nanosheets. The latter\nstructures display significant promise for the construction of hybrid\nmaterials for functional devices due to their extended planar geometry.\nRealization of this objective necessitates the ability to control\nthe structural features of the resultant assemblies through the peptide\nsequence. The design of a amphiphilic peptide, <b>3FD-IL</b>, is described that comprises two repeats of a canonical 18 amino\nacid sequence associated with straight α-helical structures.\nPeptide <b>3FD-IL</b> displays 3-fold screw symmetry in a helical\nconformation and self-assembles into nanosheets based on hexagonal\npacking of helices. Biophysical evidence from TEM, cryo-TEM, SAXS,\nAFM, and STEM measurements on the <b>3FD-IL</b> nanosheets support\na structural model based on a honeycomb lattice, in which the length\nof the peptide determines the thickness of the nanosheet and the packing\nof helices defines the presence of nanoscale channels that permeate\nthe sheet. The honeycomb structure can be rationalized on the basis\nof geometrical packing frustration in which the channels occupy defect\nsites that define a periodic superlattice. The resultant 2D materials\nmay have potential as materials for nanoscale transport and controlled\nrelease applications.