Toroidal nanostructures are symmetrical ring-shaped structures with a central internal pore. Interestingly, in nature, many transmembrane proteins such as β-barrels and α-helical bundles have toroidal shapes. Because of this similarity, toroidal nanostructures can provide a template for the development of transmembrane channels. However, because of the lack of guiding principles for the construction of toroids, researchers have not widely studied the self-assembly of toroidal nanostructures as compared with the work on other supramolecular architectures. In this Account, we describe our recent efforts to construct toroidal nanostructures through the self-assembly of rationally designed building blocks. In one strategy for building these structures, we induce interfacial curvatures within the building blocks. When we laterally graft a bulky hydrophilic segment onto a p-oligophenyl rod or β-sheet peptides, the backbones of the self-assembled structures can bend in response to the steric effect of these large side groups, driving the p-oligophenyl rod or β-sheet peptides to form nanosized toriods. In another strategy, we can build toroids from bent-shaped building blocks by stacking the macrocycles. Aromatic segments with an internal angle of 120° can associate with each other in aqueous solution to form a hexameric macrocycle. Then these macrocycles can stack on top of each other via hydrophobic and π-π interactions and form highly uniform toroidal nanostructures. We provide many examples that illustrate these guiding principles for constructing toroidal nanostructures in aqueous solution. Efforts to create toroidal nanostructures through the self-assembly of elaborately designed molecular modules provide a fundamental approach toward the development of artificial transmembrane channels. Among the various toroids that we developed, a few nanostructures can insert into lipid membranes and allow limited transport in vesicles.

Protein pores are highly specific in binding to chiral substrates and in catalysing stereospecific reactions, because their active pockets are asymmetric and stereoselective. Chiral binding materials from molecular-level pores with high specificity have not been achieved because of problems with pore deformation and blocking . A promising solution is the self-assembly of single sheets where all pores are exposed to the environment, for example as metal-organic frameworks , polymers or non-covalent aromatic networks, but, typically, the pores are distant from the internal cavities with chirality. Here, we report the synthesis of homochiral porous nanosheets achieved by the 2D self-assembly of non-chiral macrocycles, with open/closed pore switching. Pore chirality is spontaneously induced by a twisted stack of dimeric macrocycles. The porous 2D structures can serve as enantiomer sieving membranes that exclusively capture a single enantiomer in a racemic mixture solution, with uptake capacity greater than 96%. Moreover, the entrapped guests inside the pores can be pumped out by pore closing triggered by external stimuli. This strategy could provide new opportunities for controlled molecule release, as well as for artificial cells.

Here we report the spontaneous formation of switchable sheets in aqueous solution, which is based on bent-shaped aromatic amphiphiles containing m-pyridine units at the terminals and a hydrophilic dendron at the apex. The aromatic segments self-assemble into flat sheets consisting of a zigzag conformation through π-π stacking interactions. Notably, the sheets reversibly transform into helical tubules at higher concentration and into discrete dimeric macrocycles at a lower concentration in response to Ag(I) ions through reversible coordination interactions between the pyridine units of the aromatic segments and the Ag(I) ions. While maintaining the coordination bonding interactions, the helical tubules reversibly transform into the dimeric macrocycles in response to the variation in concentration.

Chiral materials are widely applied in various fields such as enantiomeric separation, asymmetric catalysis, and chiroptical effects, providing stereospecific conditions and environments. Supramolecular concepts to create the chiral materials can provide an insight for emerging chiro-optical properties due to their well-defined scaffolds and the precise functionalization of the surfaces or skeletons. Among the various supramolecular chiral structures, 2D chiral sheet structures are particularly interesting materials because of their extremely high surface area coupled with many unique chemical and physical properties, thereby offering potential for the next generation of functional materials for optically active systems and optoelectronic devices. Nevertheless, relatively limited examples for 2D chiral materials exhibiting specific functionality have been reported because incorporation of molecular chirality into 2D architectures is difficult at the present stage. Here, a brief overview of the recent advances is provided on the construction of chiral supramolecular 2D materials and their functions. The design principles toward 2D chirality and their potential applications are also discussed.

Hierarchical assemblies of biomolecular subunits can carry out versatile tasks at the cellular level with remarkable spatial and temporal precision. As an example, the collective motion and mutual cooperation between complex protein machines mediate essential functions for life, such as replication, synthesis, degradation, repair and transport. Nucleic acid molecules are far less dynamic than proteins and need to bind to specific proteins to form hierarchical structures. The simplest example of these nucleic acid-based structures is provided by a rod-shaped tobacco mosaic virus, which consists of genetic material surrounded by coat proteins. Inspired by the complexity and hierarchical assembly of viruses, a great deal of effort has been devoted to design similarly constructed artificial viruses. However, such a wrapping approach makes nucleic acid dynamics insensitive to environmental changes. This limitation generally restricts, for example, the amplification of the conformational dynamics between the right-handed B form to the left-handed Z form of double-stranded deoxyribonucleic acid (DNA). Here we report a virus-like hierarchical assembly in which the native DNA and a synthetic coat undergo repeated collective helicity switching triggered by pH change under physiological conditions. We also show that this collective helicity inversion occurs during translocation of the DNA-coat assembly into intracellular compartments. Translating DNA conformational dynamics into a higher level of hierarchical dynamics may provide an approach to create DNA-based nanomachines.