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.