Crystalline Peptoid Nanofibers with a Single-Unit Cell Cross Section

Ultranarrow crystalline one-dimensional nanostructures
formed from
soft materials facilitate precise structural control in nanomaterial
design, which is essential for biomedicine and nanotechnology applications.
Systematic control of their hierarchical structure is challenging
due to the complexities of simultaneously manipulating multiple noncovalent
interactions at such small scales. We employed a polypeptoid crystal
motif as a supramolecular synthon to engineer ultranarrow crystalline
nanofibers constrained to a single lattice axis by incorporating a
single ionizable side chain into the hydrophobic core of a nanosheet-forming
peptoid. Cryogenic transmission electron microscopy of the nanofibers
revealed detailed molecular arrangements of a unit-cell cross-section
and the presence of distinct pH-dependent lattice isoforms that resulted
in morphological transformations. Molecular dynamics simulations demonstrated
that the ionizable side chain plays a critical role in changing the
local conformation of the unit cell, which further impacts the dimensionality
of hierarchical structures. Moreover, these fibers were readily functionalized
with biological ligands to afford one-dimensional (1D) protein arrays.
This approach for the high-precision bottom-up assembly of ultranarrow
1D nanostructures offers significant potential for developing novel
biomimetic nanostructures.