Supramolecular Double Helices from Small C₃-Symmetrical Molecules Aggregated in Water

Area of Science:

• Supramolecular chemistry
• Materials science
• Nanotechnology

Background:

• Supramolecular fibers are key nanostructures for biomedical uses, formed by self-assembling amphiphilic molecules.
• Recent studies suggest helical structures in racemic form, though not fully understood.
• Benzene-1,3,5-tricarboxamides (BTAs) are water-soluble molecules used in supramolecular polymer research.

Purpose of the Study:

• To investigate the self-assembly of water-soluble BTAs into supramolecular polymers.
• To characterize the structure of these polymers, specifically addressing the formation of helical structures.
• To explore the tunability of structural parameters, such as helical pitch, through copolymer composition.

Main Methods:

• Synthesis of supramolecular (co)polymers based on benzene-1,3,5-tricarboxamides (BTAs).
• Cryogenic transmission electron microscopy (cryo-TEM) for high-resolution imaging.
• Three-dimensional volume reconstructions to analyze helical structures and repeats.

Main Results:

• BTAs self-assemble into double helical supramolecular fibers in water, not simple 1D stacks.
• Helical repeats were observed with pitches ranging from 15 to 30 nm.
• The helical pitch is tunable by adjusting the ratio of different BTA monomers in copolymers.
• Dimer formation is proposed as a mechanism for hydrophobic shielding, promoting double helix formation.

Conclusions:

• Supramolecular BTA polymers form thermodynamically stable double helical structures in water.
• The findings challenge the long-held view of 1D molecular stacking in such fibers.
• Detailed structural analysis is crucial for understanding the precise molecular arrangement in 1D supramolecular fibers.