Amplification of Molecular Asymmetry during the Hierarchical Self-Assembly of Foldable Azobenzene Dyads into Nanotoroids and Nanotubes

Abstract

The amplification of molecular asymmetry through self-assembly is a phenomenon that not only comprehends the origin of homochirality in nature but also produces chiroptically active functional materials from molecules with minimal enantiomeric purity. Understanding how molecular asymmetry can be transferred and amplified into higher-order structures in a hierarchical selfassembly system is important but still unexplored. Herein, we present an intriguing example of the amplification of molecular asymmetry in hierarchically self-assembled nanotubes that feature discrete and isolatable toroidal intermediates. The hierarchical self-assembly is initiated via asymmetric intramolecular folding of scissor-shaped azobenzene dyads furnished with chiral side chains. When scalemic mixtures of the enantiomers are dissolved in a non-polar solvent and cooled to 20 °C, single-handed nanotoroids are formed, as confirmed using atomic force microscopy and circular dichroism analyses. A strong majority-rules effect at the nanotoroid level is observed and can be explained by a low mismatch penalty and a high helix-reversal penalty. The single-handed nanotoroids stack upon cooling to 0 °C to exclusively afford their respective single-handed nanotubes. Thus, the same degree of amplification of molecular asymmetry is realized at the nanotube level. The internal packing efficiency of molecules within nanotubes prepared from the pure enantiomers or their scalemic mixtures is likely different, as suggested by the absence of higher-order structure (supercoil) formation in the latter. Xray diffraction analysis of the anisotropically oriented nanotube films revealed looser molecular packing within the scalemic nanotubes, which clearly reflects the lower enantiomeric purity of their internal chiral side chains.

Materials Nanoarchitectonics: Collaboration between Chem, Nano and Mat

“…tube structure and further hierarchical structures (Figure 20). [62] In hierarchically self-assembled nanotubes, molecular asymmetry is amplified. In this system, a scissors-shaped azobenzene molecule with chiral side chains is used as a building block.…”

“…Yagai and co‐workers examined whether the chiral purity of the constituent molecules is reflected in the assembled nanotube structure and further hierarchical structures (Figure 20). [62] In hierarchically self‐assembled nanotubes, molecular asymmetry is amplified. In this system, a scissors‐shaped azobenzene molecule with chiral side chains is used as a building block.…”

Fine-tuning of the size of supramolecular nanotoroids suppresses the subsequent catenation of nano-[2]catenane

“…As such, nanoscale toroidal assemblies of uniform diameter can be obtained in good yield. [10][11][12][13][14] These discrete toroidal assemblies (nanotoroids) can be hierarchically organized one-dimensionally by stacking into tubular assemblies [14][15][16][17][18][19] or two-dimensionally on a substrate by densely packing into porous networks. 3,20,21 In contrast, we have recently reported an unprecedented topological organization of toroidal assemblies by mechanically interlocking into selfassembled nanocatenanes.…”

Chiral Supramolecular Multiblock Copolymerization Accompanying Chirality Transfer in Heterostructures via Living Chain Growth

“…In particular, supramolecular chirality can be generated by chirality transfer, chirality amplification, and symmetry breaking of either chiral or achiral molecules in single or multicomponent systems [24–29] . The control of chirality in complex multicomponent systems offers advantages in biomimetics and helps to better understand chirality in natural systems [30–41] . Therefore, understanding the principle of chirality transfer and chiral inversion at the supramolecular level is essential for biological and medical applications, such as drug delivery, gene delivery, tissue engineering, imaging, and sensing.…”

“…[24][25][26][27][28][29] The control of chirality in complex multicomponent systems offers advantages in biomimetics and helps to better understand chirality in natural systems. [30][31][32][33][34][35][36][37][38][39][40][41] Therefore, understanding the principle of chirality transfer and chiral inversion at the supramolecular level is essential for biological and medical applications, such as drug delivery, gene delivery, tissue engineering, imaging, and sensing.…”