Assembly of supramolecular nanotubes from molecular triangles and 1,2-dihalohydrocarbons

Hydrogen-Bonded Fibrous Nanotubes Assembled from Trigonal Prismatic Building Blocks

In reticular chemistry, molecular building blocks are designed to create crystalline open frameworks. A key principle of reticular chemistry is that the most symmetrical networks are the likely outcomes of reactions, particularly when highly symmetrical building blocks are involved. The strategy of synthesizing low-dimensional networks aims to reduce explicitly the symmetry of the molecular building blocks. Here we report the spontaneous formation of hydrogen-bonded fibrous structures from trigonal prismatic building blocks, which were designed to form three-dimensional crystalline networks on account of their highly symmetrical structures. Utilizing different microscopic and spectroscopic techniques, we identify the structures at the early stages of the assembly process in order to and understand the growth mechanism. The symmetrical molecular building blocks are incorporated preferentially in the longitudinal direction, giving rise to anisotropic hydrogen-bonded porous organic nanotubes. Entropy-driven anisotropic growth provides micrometer-scale unidirectional nanotubes with high porosity. By combining experimental evidence and theoretical modeling, we have obtained a deep understanding of the nucleation and growth processes. Our findings offer fundamental insight into the molecular design of tubular structures. The nanotubes evolve further in the transverse directions to provide extended higher-order fibrous structures [nano- and microfibers], ultimately leading to large-scale interconnected hydrogen-bonded fiber-like structures with twists and turns. Our work provides fundamental understanding and paves the way for innovative molecular designs in low-dimensional networks.

Leveraging Halogen Interactions for a Supramolecular Nanotube

We demonstrate the formation of supramolecular nanotubes from molecular triangles in a single crystal by balancing the hydrogen bonds and halogen interactions between individual macrocycles. Thereby, we template the supramolecular nanotube growth by intermolecular interactions encoded directly in the macrocycles instead of those provided by the crystallization solvent. Ultimately, we show that replacing bromines for iodines in the macrocycle is necessary to achieve this supramolecular organization by enhancing the strength of the halogen interactions and concomitant reduction of the detrimental hydrogen bonds. We investigated the nature and the interplay of the individual intermolecular interactions by analysis of the experimental single crystal data and quantum chemical calculations. This work enriches the available toolbox of supramolecular interactions and will aid and abet the development of rationally-designed materials with a long-range 1D tubular organization.

Two-ring chirality generated by the alignment of two achiral phenylacetylene macrocycles

When two achiral rings are bound mechanically, a chiral source is generated in the assembly. The chiroptical properties could be modulated according to the relative occupation of each ring in the assembly. In fact, we have found that two isomeric assemblies (1 and 2) show unique properties in each assembly with two achiral rings of phenylacetylene macrocycle (PAM). When considering the difference in the chiroptical properties of these two isomeric assemblies (6PAM × 2), no comparison was available based on no activity of the achiral component element itself (6PAM). In this work, we synthesized a two-ring chiral analog (4) by the ring-fusion of two 6PAMs to an 11PAM, and examined the chiroptical properties of 4, since the single helix was imparted as a chiral source. By comparison of the chiroptical properties (molar circular dichroism and molar optical rotation) of 1 and 2 to those of 4, we demonstrated that the disparity was related to the alignment of the two achiral rings.

Assembling of Perylene, Naphthalene, and Pyromellitic Diimide-Based Materials and Their Third-Order Nonlinear Optical Properties

π-conjugated aromatic diimides with chemical stability, heat resistance, and redox activity have attracted more attention due to their excellent fluorescence quantum yield in solution. The planar perylene diimide (PDI) derivatives generally have aggregation-induced emission quenching in the solid state, while the cyclic trimers based on pyromellitic diimides (PMDIs), naphthalene diimides (NDIs), and PDIs can increase the fluorescence quantum yield in the solid state and have large two-photon absorption cross section, which can be used as excellent nonlinear optical (NLO) materials. Therefore, this paper will study the effects of multiple assembly modes of the three monomers on the NLO responses of materials. It was found that the assembly modes of 2PMDI-1NDI and 2NDI-1PDI exhibit larger third-order NLO response (γ) values, which was due to the larger conjugate surface of PDI effectively reducing the energy gap between the HOMO and LUMO. Compared with other assembly methods, 2PMDI-1NDI and 2NDI-1PDI were conducive to causing redshifts (150 nm) in the absorption spectrum. Therefore, the larger conjugate surface of PDI and the assembly mode of the isosceles triangle were more favorable for intramolecular charge transfer, thus improving its NLO properties.

Recent Advances in the Synthesis and Applications of Nitrogen-Containing Macrocycles

Macrocyclic nitrogen-containing compounds are versatile molecules. Supramolecular, noncovalent interactions of these macrocycles with guest molecules enables them to act as catalysts, fluorescent sensors, chiral or nonchiral selectors, or receptors of small molecules. In the solid state, they often display a propensity to form inclusion compounds. All of these properties are usually closely connected with the presence of nitrogen atoms in the macrocyclic ring. As most of the reviews published so far on macrocycles were written from the viewpoint of functional groups, synthetic methods, or the structure, search methods for literature reports in terms of the physicochemical properties of these compounds may be unobvious. In this minireview, the emphasis was put on the synthesis and applications of nitrogen-containing macrocyclic compounds, as they differ from their acyclic analogs, and at the same time are the driving force for further research.

Structure analysis of inclusion crystals of diimide-based macrocycles with halocarbons

Inclusion crystals containing several halocarbons were formed by three types of diimide-based macrocycles. Iodomethane was encapsulated within the cavity of the macrocycle through halogen-related interactions.

Size-encoded hierarchical self-assembly of nanoparticles into chains and tubules

Hierarchical structures with sophisticated patterns allow the emergence of challenging properties. However, the highly cooperative and specific interactions needed for assembly spanning different length scales are typically lacking in inorganic nanoparticles (NPs). Here we show that size can be a common structural driving force for controlling hierarchical assembly of inorganic NPs into anisotropic superstructures. It involves first the self-limiting assembly of small CdS NPs into large supraparticles and their subsequent spontaneous organization into chains and tubules hundreds of nanometers long. Our quantitative calculations based on DLVO theory reveals an intrinsic size effect relating to the dimension change of assembly units in accordance with a negative cooperativity. It is shown that the size increase in building blocks creates an effective kinetic barrier contrast at different attachment sites due to the increase of interparticle electrostatic repulsion, switching the assembly from thermodynamically preferred 3D to kinetically favored 1D pathway. The size-encoded hierarchical assembly is accompanied by the ligand-controlled Oswald ripening process, which is responsible for the variation of hierarchical patterns from chains to tubules. The general principle in governing multistage inorganic NP ordering represents an important guideline toward the complex mesoscale structures that may surpass traditional materials in both design and functionality.

Bamboo-like π-Nanotubes with Tunable Helicity and Circularly Polarized Luminescence

We report the fabrication of an exotic bamboo-like π-nanotube via the hierarchical self-assembly of a dipeptide-substituted naphthalenediimide gelator with tunable helicity and circularly polarized luminescence (CPL). It was found that in the presence of trifluoroacetic acid (TFA) the gelator molecules self-assembled into a bamboo-like π-nanotube, which is composed of truncated nanocones and CPL active. When defining the diameter ratio of the lower to upper edge of each nanocone as a parameter to express the helicity of different nanotubes, it was found that both the helicity and CPL of these nanotubes can be adjusted by the amount of TFA. Moreover, the helicity of the nanotube can be conveyed to the achiral quantum dots (QDs) and produce a hybrid nanotube/QDs CPL active materials with adjustable dissymmetry factor. This work finds a new type self-assembled bamboo-like π-nanotube and unveils their helicity and CPL control.

Molecular Triangles: A New Class of Macrocycles

ConspectusMacrocycles have had a profound influence on the establishment of supramolecular chemistry because of their abundant molecular recognition and self-assembly characteristics. The design of new macrocyclic receptors that can be tailored by synthesis to display new and exotic properties is an important research objective for chemists and materials scientists. Rigid macrocycles with π-conjugated aromatic units, in contrast with flexible ones, tend to possess large interior and exterior π-surfaces in addition to persistent shapes. These features not only endow these macrocycles with a wide range of host-guest properties but also render them ideal building blocks for constructing a diverse variety of supramolecular architectures. The incorporation of π-conjugated units into macrocycles also imbues them with a wealth of optical, electronic, and magnetic properties, resulting in their broad application in materials science and molecular nanotechnology.Recently, we have designed and synthesized a new class of macrocycles, namely, molecular triangles, which have rigid structures with triangular geometries. They consist of three chiral trans-1,2-cyclohexano apexes and three aromatic tetracarboxylic diimide linkers, such as pyromellitic diimide, naphthalene diimide, and perylene diimide. Benefiting from the availability of facile synthetic protocols, the geometries and properties of these rigid molecular triangles can be altered at will. By combining these tetracarboxylic diimide linkers, we have been able to synthesize both molecular equilateral and isosceles triangles. During the past few years, we have conducted research in a systematic manner on the structural features and self-assembly characteristics of these molecular triangles. The following points are worthy of note regarding these molecular triangles: (i) They possess shape-persistent inner cavities of a highly electron-deficient nature. These features endow them with the ability to complex with anions and electron-rich molecules, forming supramolecular nanotubes and two-dimensional tilings. (ii) Those with intrinsic chirality are able to self-assemble into solid-state nonhelical or single-handed helical superstructures, inducing selective chirality transfer from the macrocycles to their crystalline supramolecular assemblies. (iii) The triangular arrangement of aromatic tetracarboxylic diimide linkers contributes to through-space electron delocalization encompassing the entire macrocycle, conferring exotic electronic and spin properties. To date, the family of molecular triangles has exhibited a range of physicochemical properties, such as anion recognition, chiral assembly, supramolecular gelation, energy storage, solid-state luminescence, and nonlinear optical response.In this Account, we summarize our recent progress in research into these molecular triangles. We present an overview of their design and synthesis, as well as a general summary of their structural features. Thereafter, we discuss state-of-the-art developments in relation to their molecular recognition properties and their assembly characteristics. In addition, we highlight the potential applications of these molecular triangles and their complexes with a range of solvents and electron-rich molecules. Finally, we speculate on further structural modifications and application-oriented explorations based on this class of molecular triangles.

Self-Assembly of Metallo-Supramolecules with Dissymmetrical Ligands and Characterization by Scanning Tunneling Microscopy

Asymmetrical and dissymmetrical structures are widespread and play a critical role in nature and life systems. In the field of metallo-supramolecular assemblies, it is still in its infancy for constructing artificial architectures using dissymmetrical building blocks. Herein, we report the self-assembly of supramolecular systems based on two dissymmetrical double-layered ligands. With the aid of ultra-high-vacuum, low-temperature scanning tunneling microscopy (UHV-LT-STM), we were able to investigate four isomeric structures corresponding to four types of binding modes of ligand LA with two major conformations complexes A. The distribution of isomers measured by STM and total binding energy of each isomer obtained by density functional theory (DFT) calculations suggested that the most abundant isomer could be the most stable one with highest total binding energy. Finally, through shortening the linker between inner and outer layers and the length of arms, the arrangement of dissymmetrical ligand LB could be controlled within one binding mode corresponding to the single conformation for complexes B.

A water-soluble naphthalenediimide-containing hexacationic cage

A water-soluble cage containing three naphthalenediimide (NDI) units was synthesized in a one-pot manner without chromatographic purification, during which six irreversible C-N bonds formed simultaneously via an SN2 reaction. The cage was observed to be capable of accommodating a variety π-electron rich guests in a peripheral manner in water. However, for linear guests including I3- and I2, the cage is able to form an inclusion complex. Besides, in the solid state, the cage can absorb vapor of I2.

3D supramolecular chiral crystal structures of radical anion salts of (−)-NDI-Δ and possible magnetic phase diagrams

Supramolecular chiral crystals of radical anion salts of a triangular chiral electron acceptor, (−)-naphthalene diimide (NDI)-Δ, were electrochemically grown in propylene carbonate electrolyte solutions in the presence of cyclic multidentate ligands.

Two-photon excited deep-red and near-infrared emissive organic co-crystals

Two-photon excited near-infrared fluorescence materials have garnered considerable attention because of their superior optical penetration, higher spatial resolution, and lower optical scattering compared with other optical materials. Herein, a convenient and efficient supramolecular approach is used to synthesize a two-photon excited near-infrared emissive co-crystalline material. A naphthalenediimide-based triangular macrocycle and coronene form selectively two co-crystals. The triangle-shaped co-crystal emits deep-red fluorescence, while the quadrangle-shaped co-crystal displays deep-red and near-infrared emission centered on 668 nm, which represents a 162 nm red-shift compared with its precursors. Benefiting from intermolecular charge transfer interactions, the two co-crystals possess higher calculated two-photon absorption cross-sections than those of their individual constituents. Their two-photon absorption bands reach into the NIR-II region of the electromagnetic spectrum. The quadrangle-shaped co-crystal constitutes a unique material that exhibits two-photon absorption and near-infrared emission simultaneously. This co-crystallization strategy holds considerable promise for the future design and synthesis of more advanced optical materials.

Two Orthogonal Halogen-Bonding Interactions Directed 2D Crystalline Supramolecular J-Dimer Lamellae

Dye assemblies exhibit fascinating properties and performances, both of which depend critically on the mutual packing arrangement of dyes and on the supramolecular architecture. Herein, we engineered, for the first time, an intriguing chlorosome-mimetic 2D crystalline J-dimer lamellar structure based on halogenated dyes in aqueous media by employing two distinct orthogonal halogen-bonding (XB) interactions. As the only building motif, antiparallel J-dimer was formed and stabilized by single π-stacking and dual halogen⋅⋅⋅π interactions. With two substituted halogen atoms acting as XB donors and the other two acting as acceptors, the constituent J-dimer units were linked by quadruple highly-directional halogen⋅⋅⋅halogen interactions in a staggered manner, resulting in unique 2D lamellar dye assemblies. This work champions and advances halogen-bonding as a remarkably potent tool for engineering dye aggregates with a controlled molecular packing arrangement and supramolecular architecture.

Site-selective [2 + 2 + n] cycloadditions for rapid, scalable access to alkynylated polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are attractive synthetic building blocks for more complex conjugated nanocarbons, but their use for this purpose requires appreciable quantities of a PAH with reactive functional groups. Despite tremendous recent advances, most synthetic methods cannot satisfy these demands. Here we present a general and scalable [2 + 2 + n] (n = 1 or 2) cycloaddition strategy to access PAHs that are decorated with synthetically versatile alkynyl groups and its application to seven structurally diverse PAH ring systems (thirteen new alkynylated PAHs in total). The critical discovery is the site-selectivity of an Ir-catalyzed [2 + 2 + 2] cycloaddition, which preferentially cyclizes tethered diyne units with preservation of other (peripheral) alkynyl groups. The potential for generalization of the site-selectivity to other [2 + 2 + n] reactions is demonstrated by identification of a Cp₂Zr-mediated [2 + 2 + 1]/metallacycle transfer sequence for synthesis of an alkynylated, selenophene-annulated PAH. The new PAHs are excellent synthons for macrocyclic conjugated nanocarbons. As a proof of concept, four were subjected to alkyne metathesis catalysis to afford large, PAH-containing arylene ethylene macrocycles, which possess a range of cavity sizes reaching well into the nanometer regime. Notably, these high-yielding macrocyclizations establish that synthetically convenient pentynyl groups can be effective for metathesis since the 4-octyne byproduct is sequestered by 5 Å MS. Most importantly, this work is a demonstration of how site-selective reactions can be harnessed to rapidly build up structural complexity in a practical, scalable fashion.

An orthogonal [2 + 2 + n] cycloaddition/alkyne metathesis reaction sequence enables streamlined access to conjugated macrocyclic nanocarbons.

Charge transfer co-crystals based on donor–acceptor interactions for near-infrared photothermal conversion

The charge transfer from the donor to the acceptor units results in a CT complex with excellent near-infrared photothermal conversion efficiency, which acted as an excellent photothermal material in seawater desalination application.

Multifunctional supramolecular self-assembly system for colorimetric detection of Hg2+, Fe3+, Cu2+ and continuous sensing of volatile acids and organic amine gases

A novel multifunctional gelator (1) based on an azobenzene derivative was designed and characterized. This compound could gelate some solvents including hexane, petroleum ether, DMSO, acetonitrile and ethanol through a heating-cooling procedure. The self-assembly process in different solvents was studied by means of UV-vis absorption and Fourier transform infrared (FTIR) spectra, field emission scanning electron microscopy (FESEM), rheological measurements, X-ray powder diffraction and water contact angle experiments. Interestingly, compound 1 had a high-contrast colorimetric detection ability towards Hg2+, Cu2+, Fe3+ and volatile acids and further organic amine gases in solution through its color change. At the same time, organogel 1 in acetonitrile also exhibited detection performance through a color or gel state change. In the response process, the self-assembly structures were changed from a nanofiber into a microsphere under induction by analytes. More significantly, film 1 could continuously detect volatile acids and organic amine gases. The number of cycles of film 1 for the detection of volatile acids and organic amine gases was at least seven times. The limit of detection (LOD) of film 1 towards TFA was calculated to be 0.0848 ppb. The sensing mechanisms were studied using 1HNMR, FESEM, UV-vis absorption spectra and HRMS. The intramolecular cyclization occurred on molecule 1 and a H2S molecule was lost during the detection process of Hg2+. It was proposed that the -N[double bond, length as m-dash]N- bonding could be coordinated by Fe3+ and Cu2+ and this further induced the absorption spectra and color change. For a volatile acid, it was possible that the volatile acid was combined with the N,N-dimethyl amine group of molecule 1. This research opens up a novel pathway to the fabrication of supramolecular self-assembly gels to detect polymetallic ions and trace volatile acids in the environment.

Self-Assembly of C3 Symmetric Rigid Macrolactams into Very Polar and Porous Trigonal Crystals

Cyclohexane and cyclotri-β-alanyl have been used as scaffolds for the design of new C₃ -symmetric rings incorporating conjugated alkenes and dienes. All three C₃ -symmetric lactams share the same triangular shape and their crystal system is trigonal. They all belong to the R3 space group, R3m, R3 and R3c, for the increasingly large 12-, 18- and 24-membered rigid rings, respectively. All lactams stack on top of each other, through H-bonds and van der Waals noncovalent interactions, leading to endless supramolecular cylinders and tubes. The largest member of the family leads to tubes, the central pores of which is wide enough to let water in. A common feature of all the lactams is their very large dipole, of around 9 D, according to DFT calculations. Surprisingly, all the resulting cylinders and tubes pack side by side in the crystals, with all the dipoles pointing to the same direction. As a result, all three crystals are anisotropic and appear to be the first members of a new kind of highly polar crystals.

Discrete Dimers of Redox-Active and Fluorescent Perylene Diimide-Based Rigid Isosceles Triangles in the Solid State

The development of rigid covalent chiroptical organic materials, with multiple, readily available redox states, which exhibit high photoluminescence, is of particular importance in relation to both organic electronics and photonics. The chemically stable, thermally robust, and redox-active perylene diimide (PDI) fluorophores have received ever-increasing attention owing to their excellent fluorescence quantum yields in solution. Planar PDI derivatives, however, generally suffer from aggregation-caused emission quenching in the solid state. Herein, we report on the design and synthesis of two chiral isosceles triangles, wherein one PDI fluorophore and two pyromellitic diimide (PMDI) or naphthalene diimide (NDI) units are arranged in a rigid cyclic triangular geometry. The optical, electronic, and magnetic properties of the rigid isosceles triangles are fully characterized by a combination of optical spectroscopies, X-ray diffraction (XRD), cyclic voltammetry, and computational modeling techniques. Single-crystal XRD analysis shows that both isosceles triangles form discrete, nearly cofacial PDI-PDI π-dimers in the solid state. While the triangles exhibit fluorescence quantum yields of almost unity in solution, the dimers in the solid state exhibit very weak-yet at least an order of magnitude higher-excimer fluorescence yield in comparison with the almost completely quenched fluorescence of a reference PDI. The triangle containing both NDI and PDI subunits shows superior intramolecular energy transfer from the lowest excited singlet state of the NDI to that of the PDI subunit. Cyclic voltammetry suggests that both isosceles triangles exhibit multiple, easily accessible, and reversible redox states. Applications beckon in arenas related to molecular optoelectronic devices.

Structure and luminescence properties of supramolecular polymers of amphiphilic aromatic thioether–peptide conjugates in water

We present the preparation of luminophore–peptide conjugates that self-assemble into phosphorescent supramolecular polymers in neutral buffer.

Supramolecular nanochannels self-assembled by helical pyridine–pyridazine oligomers

We present a novel helix-based supramolecular nanochannel, wherein alkali ions could be easily collected, transported and even controllably released.

Air–water interfacial assembly of all-aromatic-substituted double-decker phthalocyanine forms aligned nanoparticles

In this manuscript, unexpected supramolecular assembly of [Formula: see text]-conjugated molecules containing complex aromatic substituents was investigated. The air–water interfacial assembly of double-decker phthalocyanines containing sixteen phenol substituents (Ce(Pc2)[Formula: see text] and Y(Pc2)[Formula: see text] form aligned nanoparticles. Depending on the different surface pressure, the Ce(Pc2)[Formula: see text] self-assembled nanostructures can be regulated thoroughly. Although Ce(Pc2)[Formula: see text] and Y(Pc2)[Formula: see text] have only aromatic substituent groups, no H- or J-aggregation of [Formula: see text]-conjugated systems can be detected from the UV-vis spectra of the assemblies of these double-decker phthalocyanines. When the nanostructures of these assemblies were changed greatly, no corresponding changes of UV-vis spectra and FT-IR spectra could be detected. These unusual results can be understood from the balance between the hydrophilicity of aromatic substituents and the ether linkages of double-decker phthalocyanines and the surface pressure, and open new. approaches for supramolecular assembly of complex [Formula: see text]-conjugated systems.

The Cucurbit[7]Uril-Based Supramolecular Chemistry for Reversible B/Z-DNA Transition

As a left-handed helical structure, Z-DNA is biologically active and it may be correlated with transcription and genome stability. Until recently, it remained a significant challenge to control the B/Z-DNA transition under physiological conditions. The current study represents the first to reversibly control B/Z-DNA transition using cucurbit[7]uril-based supramolecular approach. It is demonstrated that cucurbit[7]uril can encapsulate the central butanediamine moiety [HN(CH2)4NH] and reverses Z-DNA caused by spermine back to B-DNA. The subsequent treatment with 1-adamantanamine disassembles the cucurbit[7]uril/spermine complex and readily induces reconversion of B- into Z-DNA. The DNA conformational change is unequivocally demonstrated using different independent methods. Direct evidence for supramolecular interactions involved in DNA conformational changes is further provided. These findings can therefore open a new route to control DNA helical structure in a reversible way.

Controlled Self-Assembly of Photofunctional Supramolecular Nanotubes

Designing supramolecular nanotubes (SNTs) with distinct dimensions and properties is highly desirable, yet challenging, since structural control strategies are lacking. Furthermore, relatively complex building blocks are often employed in SNT self-assembly. Here, we demonstrate that symmetric bolaamphiphiles having a hydrophobic core comprised of two perylene diimide moieties connected via a bipyridine linker and bearing polyethylene glycol (PEG) side chains can self-assemble into diverse molecular nanotubes. The structure of the nanotubes can be controlled by assembly conditions (solvent composition and temperature) and a PEG chain length. The resulting nanotubes differ both in diameter and cross section geometry, having widths of 3 nm (triangular-like cross-section), 4 nm (rectangular), and 5 nm (hexagonal). Molecular dynamics simulations provide insights into the stability of the tubular superstructures and their initial stages of self-assembly, revealing a key role of oligomerization via side-by-side aromatic interactions between bis-aromatic cores. Probing electronic and photonic properties of the nanotubes revealed extended electron delocalization and photoinduced charge separation that proceeds via symmetry breaking, a photofunction distinctly different from that of the fibers assembled from the same molecules. A high degree of structural control and insights into SNT self-assembly advance design approaches toward functional organic nanomaterials.

Quantified structural speciation in self-sorted CoII6L4 cage systems

The molecular components of biological systems self-sort in different ways to function cooperatively and to avoid interfering with each other. Understanding the driving forces behind these different sorting modes enables progressively more complex self-assembling synthetic systems to be designed. Here we show that subtle ligand differences engender distinct M₆L₄ cage geometries - an S₄-symmetric scalenohedron, or pseudo-octahedra having T point symmetry. When two different ligands were simultaneously employed during self-assembly, a mixture of homo- and heteroleptic cages was generated. Each set of product structures represents a unique sorting regime: biases toward specific geometries, preferential incorporation of one ligand over another, and the amplification of homoleptic products were all observed. The ligands' geometries, electronic properties, and flexibility were found to influence the sorting regime adopted, together with templation effects. A new method of using mass spectrometry to quantitatively analyse mixtures of self-sorted assemblies was developed to assess individual outcomes. Product distributions in complex, dynamic mixtures were thus quantified by non-chromatographic methods.

Cucurbit[7]uril-Driven Host-Guest Chemistry for Reversible Intervention of 5-Formylcytosine-Targeted Biochemical Reactions

5-Formylcytosine (5fC) is identified as one of the key players in active DNA demethylation and also as an epigenetic mark in mammals, thus representing a novel attractive target to chemical intervention. The current study represents an attempt to develop a reversible 5fC-targeted intervention tool. A supramolecular aldehyde reactive probe was therefore introduced for selective conversion of the 5fC to 5fC-AD nucleotide. Using various methods, we demonstrate that cucurbit[7]uril (CB7) selectively targets the 5fC-AD nucleotide in DNA, however, the binding of CB7 to 5fC-AD does not affect the hydrogen bonding properties of natural nucleobases in duplex DNA. Importantly, CB7-driven host-guest chemistry has been applied for reversible intervention of a variety of 5fC-targeted biochemical reactions, including restriction endonuclease digestion, DNA polymerase elongation, and polymerase chain reaction. On the basis of the current study, the macrocyclic CB7 creates obstructions that, through steric hindrance, prevent the enzyme from binding to the substrate, whereas the CB7/5fC-AD host-guest interactions can be reversed by treatment with adamantanamine. Moreover, fragment- and site-specific identification of 5fC modification in DNA has been accomplished without sequence restrictions. These findings thus show promising potential of host-guest chemistry for DNA/RNA epigenetics.

Reversible manipulation of the G-quadruplex structures and enzymatic reactions through supramolecular host-guest interactions

Supramolecular chemistry addresses intermolecular forces and consequently promises great flexibility and precision. Biological systems are often the inspirations for supramolecular research. The G-quadruplex (G4) belongs to one of the most important secondary structures in nucleic acids. Until recently, the supramolecular manipulation of the G4 has not been reported. The present study is the first to disclose a supramolecular switch for the reversible control of human telomere G4s. Moreover, this supramolecular switch has been successfully used to manipulate an enzymatic reaction. Using various methods, we show that cucurbit[7]uril preferably locks and encapsulates the positively charged piperidines of Razo through supramolecular interactions. They can switch the conformations of the DNA inhibitor between a flexible state and the rigid G4 and are therefore responsible for the reversible control of the thrombin activity. Thus, our findings open a promising route and exhibit potential applications in future studies of chemical biology.

Chiral Nanotubes

Organic nanotubes, as assembled nanospaces, in which to carry out host-guest chemistry, reversible binding of smaller species for transport, sensing, storage or chemical transformation purposes, are currently attracting substantial interest, both as biological ion channel mimics, or for addressing tailored material properties. Nature's materials and machinery are universally asymmetric, and, for chemical entities, controlled asymmetry comes from chirality. Together with carbon nanotubes, conformationally stable molecular building blocks and macrocycles have been used for the realization of organic nanotubes, by means of their assembly in the third dimension. In both cases, chiral properties have started to be fully exploited to date. In this paper, we review recent exciting developments in the synthesis and assembly of chiral nanotubes, and of their functional properties. This review will include examples of either molecule-based or macrocycle-based systems, and will try and rationalize the supramolecular interactions at play for the three-dimensional (3D) assembly of the nanoscale architectures.

A dual response organogel system based on an iridium complex and a Eu(iii) hybrid for volatile acid and organic amine vapors

A thiophene-based hybrid organogel system consisting of complex iridium (Ir) and EuCl₃·6H₂O was designed and synthesized to realize dual responses to volatile acids and organic amine vapors. The photophysical properties and self-assembly of compound 1 and the hybrid organogel were also studied. Compound 1 could gelate some organic solvents and self-assemble into 3D nanofibers in the gels. The stable hybrid organogel 1-Ir-Eu could be obtained after addition of complex Ir and EuCl₃·6H₂O. FTIR spectral results showed that the hydrogen bond still remained even upon addition of complex Ir, EuCl₃·6H₂O, NaOH and CF₃COOH to organogel 1. Interestingly, the emission properties of the hybrid organogel 1-Ir-Eu could undergo interconversion between cyan light and red light via addition of NaOH and CF₃COOH. The emission properties of xerogel film 1-Ir-Eu obtained in the presence of NaOH could also undergo fast and reversible transition in response to volatile acids such as CF₃COOH, formic acid, acetic acid, propionic acid and organic amine vapors such as ammonium hydroxide, Et₃N, tripropylamine, and ethylenediamine. The emission spectral change of Ir-Eu in the organogel or xerogel in the presence of base and acid demonstrated the formation of a new complex between complex Ir and EuCl₃·6H₂O. This dual-response process could be repeated many times. Contact angle experiment results further showed the morphology and internal components of the xerogel film surface in the process of response to gaseous CF₃COOH and Et₃N. This work provides a method for producing multifunctional supramolecular materials for sensing volatile acids and organic amine vapors.

Towards stable porous crystalline phases of molecular belts

A chemical modification of a molecular belt (M1) renders the molecule (M2) into a stable supramolecular nanotube porous crystal.

Donor–acceptor single cocrystal of coronene and perylene diimide: molecular self-assembly and charge-transfer photoluminescence

Organic semiconductor molecules, coronene and perylene diimide, form an alternate stacked cocrystal due to the strong donor–acceptor charge transfer interaction.

Surveying macrocyclic chemistry: from flexible crown ethers to rigid cyclophanes

This review features the progress made in the development of macrocycles since Pedersen's ground-breaking discovery of the crown ethers in 1967.

Recent advances in controlling the internal and external properties of self-assembling cyclic peptide nanotubes and dimers

Tuning the internal and external properties of self-assembling cyclic peptide nanotubes.