Three-Dimensional Crystals Assembled by Linear Oligopeptoids

The rational construction of three-dimensional (3D) crystalline
lattices from synthetic short-chain polymers remains a significant
challenge due to the lack of inherent driving forces to enable crystal
growth in all three dimensions. Here, we report the design of 3D peptoid
crystals from linear peptoid hexamers, derived from amphiphilic diblock
sequences that typically form crystalline two-dimensional (2D) nanosheets.
By removing the amorphous domains and tuning the chain termini, crystalline
lamellae up to 500 nm thick were achieved, far exceeding the thickness
of typical nanosheets (on the order of a few nanometers). These 3D
crystals form via the stacking of unit cells with lattice parameters
similar to those in 2D nanosheets, where terminal groups, particularly
compact C-terminal moieties, facilitate vertical growth and enhance
crystallinity. This study highlights the importance of atomic precision
in terminus chemistry for achieving long-range ordering and isotropic
crystal growth in the design of macroscale crystals from oligomeric
peptoids.