National Taiwan University: NTU Research Team Builds the Largest Supramolecular Cuboctahedron

S-layers are commonly seen in prokaryotic organisms and play an important role in cell protection and surface interactions. These layers are composed of identical proteinaceous subunits that can self-assemble into ordered porous 2D arrays of 5-15 nm thickness and unit cell sizes in the range of 3-30 nm. To explore how protein motifs can be tiled into 2D crystalline materials, a research team led by Professor Yi-Tsu Chan of NTU’s Department of Chemistry researched porous layers assembled from artificially synthesized molecules of similar dimensions to explore the construction of giant well-defined building units.

Inspired by Buckminster Fuller’s concept of tensegrity (tensional integrity), the team developed a precise coordination-driven self-assembly methodology for the rational construction of a molecular cuboctahedron with a circumscribed sphere diameter of over 10 nm. The result not only marks a significant breakthrough in the area of chemical mimicry of S-layer self-assembly but is also the largest synthetic cuboctahedron reported to date.

The cuboctahedron is assembled from 76 subcomponents and has a double-layered structure, resembling a tensegrity architectural structure. It is worth mentioning that the high stability of the cuboctahedral complex enables small-angle X-ray scattering (SAXS) measurements under dilute conditions, providing crucial structural evidence. Moreover, the team collaborated with the Academia Sinica Cryo-EM Center (ASCEM) to conduct cryo-EM experiments on the S-layer-like square arrays of the giant cuboctahedra in vitrified acetonitrile solution with a lattice constant of 7.9 nm. Through this experiment, such local packing defects as dislocations and grain boundaries in the 2D arrays were analyzed and elucidated.

The general self-assembly methodology and the serendipitous observation of S-layer-like square arrays presented in this study not only exemplify scientific discovery but also lay the foundation for developing bottom-up techniques for the construction of 2D porous supramolecular materials.