The aqueous supramolecular chemistry of cucurbit[n]urils, pillar[n]arenes and deep-cavity cavitands

Facile synthesis of a new chiral polyimine macrocycle and its application for enantioseparation in high-performance liquid chromatography

Macrocyclic compounds such as crown ethers and cyclodextrins play an important role in the field of chromatography and show excellent separation performance. The design of simple and convenient methods for the efficient synthesis of novel chiral macrocycles for chromatographic separation is of great significance. In this work, a novel chiral polyimine macrocycle (PIMC) was designed and synthesized by the simply one-step reaction of 2,6-diformyl-4-tert-butylphenol with (S)-(-)-1,2-propanediamine. Then, it was bonded onto silica by the thiol-ene click reaction to construct a new chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC). The chiral separation performance of the proposed CSP was examined by separating various racemates in the normal-phase (NP) and reversed-phase (RP) HPLC. In total, twelve and nine racemates, including ethers, esters, amines, alcohols, organic acids, ketones, and epoxides, were separated to varying degrees via NP-HPLC and RP-HPLC, respectively, Moreover, the CSP offered good chiral separation complementarity to Chiralcel OD-H and Chiralpak AD-H columns for resolution of these test racemates, and it can separate several racemic compounds that either cannot be separated or cannot be separated well be separated by the two commercially available columns. After the column was used for hundreds of injections, the relative standard deviations of the retention time and resolution were below 0.56 % and 0.45 %, respectively, showing the good reproducibility and stability of the CSP. This study provides a simple and convenient approach to synthesize a novel chiral macrocycle and CSP and also indicates the broad application prospects of such chiral PIMCs in HPLC chiral separation.

Cucurbit[8]uril-Mediated Supramolecular Heterodimerisation and Photoinduced [2+2] Heterocycloaddition to Generate Unexpected [2]Rotaxanes

In contrast to the self-assembly of homosupramolecules, the self-assembly of heterosupramolecules is more challenging and significant in various fields. Herein, we design and investigate a cucurbit[8]uril-mediated heterodimerisation based on an arene-fluoroarene strategy. Furthermore, the heteroternary complex is found to be able to undergo a photoinduced [2+2] heterocycloaddition, resulting in the formation of an unexpected [2]rotaxane. This work demonstrates a novel supramolecular heterodimerisation system that not only contributes to the development of photoisomerisation systems, but also enriches synthetic methods for mechanically interlocked molecules.

Preparation and evaluation of a 1,1'-bi-2-naphthol-based chiral macrocycle bonded silica chiral stationary phase for high performance liquid chromatography

Macrocycles play vital roles in supramolecular chemistry and chromatography. 1,1'-Bi-2-naphthol (BINOL)-based chiral polyimine macrocycles are an emerging class of chiral macrocycles that can be constructed by one-step aldehyde-amine condensation of BINOL derivatives with other building blocks. These macrocycles exhibit good characteristics, such as facile preparation, rigid cyclic structures, multiple chiral centers, and defined molecular cavities, that make them good candidates as new chiral recognition materials for chromatographic enantioseparations. In this study, a BINOL-based [2+2] chiral polyimine macrocycle was synthesized by one-step condensation of enantiopure (S)-2,2'-dihydroxy-[1,1'-binaphthalene]-3,3'-dicarboxaldehyde with (1R,2R)-1,2-diaminocyclohexane. The product was modified with 5-bromo-1-pentene and then attached to thiolated silica using click chemistry to construct a new chiral stationary phase (CSP). The enantioselectivity of the new CSP was explored by separating various racemates under normal phase (NP) and reversed phase (RP) high performance liquid chromatography (HPLC). Thirteen racemates and eight racemates were enantioseparated under the two separation modes, respectively, including chiral alcohols, phenols, esters, ketones, amines, and organic acids. Among them, nine racemates achieved baseline separation under NP-HPLC and seven racemates achieved baseline separation under RP-HPLC. High resolution separation was observed with benzoin (Rs = 5.10), epinephrine (Rs = 4.98), 3-benzyloxy-1,2-propanediol (Rs = 4.42), and 4,4'-dimethylbenzoin (Rs = 4.52) in NP-HPLC, and with 4-methylbenzhydrol (Rs = 4.72), benzoin ethyl ether (Rs = 3.79), 1-phenyl-1-pentanol (Rs = 3.68), and 1-(3-bromophenyl)ethanol (Rs = 3.60) in RP-HPLC. Interestingly, the CSP complemented Chiralcel OD-H, Chiralpak AD-H, and CYCLOBOND I 2000 RSP columns for resolution of these test racemates, separating several racemic compounds that could not be well separated by the three commercially available columns. The influences of injected sample amount on separation were also evaluated. It was found that the column exhibited excellent stability and reproducibility after hundreds of injections, and the relative standard deviations (n = 5) of the retention time and resolution were less than 0.49% and 0.69%, respectively. This study indicates that the BINOL-based chiral macrocycle has great potential for HPLC enantioseparation.

A Supramolecular Biosensor for Rapid and High-Throughput Quantification of a Disease-Associated Niacin Metabolite

Metabolic abnormalities play a pivotal role in various pathological conditions, necessitating the quantification of specific metabolites for diagnosis. While mass spectrometry remains the primary method for metabolite measurement, its limited throughput underscores the need for biosensors capable of rapid detection. Previously, we reported that pillar[6]arene with 12 carboxylate groups (P6AC) forms host-guest complexes with 1-methylnicotinamide (1-MNA), which is produced in vivo by nicotinamide N-methyltransferase (NNMT). P6AC acts as a biosensor by measuring the fluorescence quenching caused by photoinduced electron transfer upon 1-MNA binding. However, the low sensitivity of P6AC makes it impractical for detecting 1-MNA in unpurified biological samples. In this study, we found that P6A with 12 sulfonate groups (P6AS) is a specific and potent supramolecular host for 1-MNA interactions even in biological samples. The 1-MNA binding affinity of P6AS in water was found to be (5.68 ± 1.02) × 106 M-1, which is approximately 700-fold higher than that of P6AC. Moreover, the 1-MNA detection limit of P6AS was determined to be 2.84 × 10-7 M, which is substantially lower than that of P6AC. Direct addition of P6AS to culture medium was sufficient to quantify 1-MNA produced by cancer cells. Furthermore, this sensor was able to specifically detect 1-MNA even in unpurified human urine. P6AS therefore enables rapid and high-throughput quantification of 1-MNA, and further improvement of our strategy will contribute to the establishment of high-throughput screening of NNMT inhibitors, diagnosis of liver diseases, and imaging of human cancer cells in vivo.

Hollow spherical nano-traps using pillararene-based polymer for efficient uranium extraction from seawater

Herein, a hollow spherical pillar[5]arene-based polymer (P5-AO) adsorbent was synthesized. The P5-AO adsorbent was capable of effectively capturing uranium from simulated seawater (139.5 mg g-1) and real seawater (8.1 mg g-1). We also elucidated the uranium adsorption mechanism of P5-AOvia extended X-ray absorption fine structure (EXAFS). This study provides a novel direction for the development of uranium capture adsorbents.

Structural Deformations in Cucurbit[n]urils: Analysis, Host-Guest Dependence, and Automated Ellipticity Measurements Using ElliptiCB[n]

Cucurbit[n]urils (CB[n]s) are cyclic macrocycles with rich host-guest chemistry. In many cases, guest binding in CB[n]s results in host structural deformations. Unfortunately, measuring such deformations remains a major challenge, with only a handful of manual estimations reported in the literature. To address this challenge, we have developed the public program ElliptiCB[n], which is available on GitHub, that provides a robust and automated method for measuring the elliptical deformations in CB[n] hosts. We outline the development and validation of this approach, apply ElliptiCB[n] to measure the ellipticity of the 1113 available CB[n] structures from the Cambridge Structural Database (CSD), and directly investigate the structural deformations of CB[5], CB[6], CB[7], CB[8], and CB[10] hosts. We also report the general landscape of accessible CB[n] elliptical deformations and compare ellipticity distributions across CB[n] hosts and host-guest complexes. We found that in almost all cases guest binding significantly impacts the distribution of host ellipticity distributions and that these distributions are dissimilar across host-guest complexes of differently sized CB[n]s. We anticipate that this work will provide a useful approach for understanding of the flexibility of CB[n] hosts and will also enable future measurement and standardization of ellipticity measurements of CB[n]s.

Triphenylamine[3]arenes: Streamlining Synthesis of a Versatile Macrocyclic Platform for Supramolecular Architectures and Functionalities

Triphenylamine[3]arenes (TPA[3]s), featuring [16]paracyclophane backbone with alternating carbon and nitrogen bridging atoms, were synthesized through a BF3 ⋅ Et2O-catalyzed cyclization reaction using triphenylamine derivatized monomers and paraformaldehyde. This molecular design yielded a series of TPA[3] macrocycles with high efficiency, with their facile derivatizations also successfully demonstrated. On account of the strong electron-donating properties of the TPA moieties, these TPA[3]s exhibit remarkable delayed fluorescence, and possess a significant affinity for iodine. Furthermore, their inherent three-fold symmetry rendered TPA[3]s as novel building blocks for the construction of extended frameworks and molecular cages. This advancement expands the versatility of discrete macrocycles into complex architectures, enhancing their applicability across a broad spectrum of applications.

Supramolecular delivery of dinuclear ruthenium and osmium MCU inhibitors

The transmembrane protein known as the mitochondrial calcium uniporter (MCU) mediates the influx of calcium ions (Ca2+) into the mitochondrial matrix. An overload of mitochondrial Ca2+ ( m Ca2+) is directly linked to damaging effects in pathological conditions. Therefore, inhibitors of the MCU are important chemical biology tools and therapeutic agents. Here, two new analogues of previously reported Ru- and Os-based MCU inhibitors Ru265 and Os245, of the general formula [(C10H15CO2)M(NH3)4(μ-N)M(NH3)4(O2CC10H15)](CF3SO3)3, where M = Ru (1) or Os (2), are reported. These analogues bear adamantane functional groups, which were installed to act as guests for the host molecule cucurbit-[7]-uril (CB[7]). These complexes were characterized and analyzed for their efficiency as guests for CB[7]. As shown through a variety of spectroscopic techniques, each adamantane ligand is encapsulated into one CB[7], affording a supramolecular complex of 1 : 2 stoichiometry. The biological effects of these compounds in the presence and absence of two equiv. CB[7] were assessed. Both complexes 1 and 2 exhibit enhanced cellular uptake compared to the parent compounds Ru265 and Os245, and their uptake is increased further in the presence of CB[7]. Compared to Ru265 and Os245, 1 and 2 are less potent as m Ca2+ uptake inhibitors in permeabilized cell models. However, in intact cell systems, 1 and 2 inhibit the MCU at concentrations as low as 1 μM, marking an advantage over Ru265 and Os245 which require an order of magnitude higher doses for similar biological effects. The presence of CB[7] did not affect the inhibitory properties of 1 and 2. Experiments in primary cortical neurons showed that 1 and 2 can elicit protective effects against oxygen-glucose deprivation at lower doses than those required for Ru265 or Os245. At low concentrations, the protective effects of 1 were modulated by CB[7], suggesting that supramolecular complex formation can play a role in these biological conditions. The in vivo biocompatibility of 1 was investigated in mice. The intraperitoneal administration of these compounds and their CB[7] complexes led to time-dependent induction of seizures with no protective effects elicited by CB[7]. This work demonstrates the potential for supramolecular interactions in the development of MCU inhibitors.

Host-Guest Chemistry in Binary and Ternary Complexes Utilizing π-Conjugated Carbon Nanorings

The carbon nanorings, possessing a radial π system, have garnered significant attention primarily due to their size-dependent photophysical properties and the presence of a unique curved π-conjugated cavity. This is evidenced by the rapid proliferation of publications. Furthermore, the integration of building blocks into CPP skeletons can confer [n]CPPs with novel and exceptional photophysical and electronic characteristics, as well as chiral properties and host-guest interactions, thereby augmenting the diversity of [n]CPPs. Notably, the curved π surface structures and concave cavity of carbon nanorings enable them to host aromatic or non-aromatic guests with a complementarily curved surface, resulting in interesting binary or ternary complexes. This review provides a comprehensive treatment of literature reports on binary and ternary complexes, focusing on both their host-guest interactions and properties. It is important to note that the scope of this review is limited to host-guest chemistry in binary and ternary complexes based on π-conjugated carbon nanorings.

Self-Inclusion Complexation of Electron-Accepting Guest into Electron-Donating Cyclic Host by Photoexcitation

Self-inclusion complexes consisting of host-guest conjugates are one of the unique supramolecular structures because they form in-state and out-state depending on the external stimuli. Despite many reports of the stimuli-responsive self-inclusion complex formation, study of the structural relaxation from out-state to in-state by photoexcitation has been unexplored. Herein, we report that an electron-donating host and an electron-accepting guest conjugate exhibits the structural relaxation from out-state to in-state by photoexcitation. Formation of the in-state in the excited state resulted in exciplex emission along with the locally excited emission from the out-state. Moreover, this structural relaxation by photoexcitation was suppressed not only by temperature, but also by the presence of guest molecules, resulting in changes in the ratio of the dual emission intensities.

Umbrella-Shaped Amphiphiles: Internal Alkylation of an Aromatic Micelle and Its Impact on Cavity Features

To develop new hybrid micelles with alkyl/polyaromatic core-shell structures, we synthesized umbrella-shaped amphiphiles bearing a bent anthracene dimer with a linear alkyl chain (i.e., octyl and hexadecyl groups). The amphiphiles quantitatively assemble into spherical micelles (~2-3 nm in core diameter), possessing an alkylated cavity surrounded by a polyaromatic framework, in water. The alkylation significantly enhances the stability of the micellar structures against dilution (up to 9 μM) and heat (up to >120 °C). The highly condensed hexadecyl core of the hybrid micelle, as indicated by solvatochromic guest probes, displays increased uptake ability toward large alkylated metallodyes. Interestingly, efficient uptake of aromatic macrocycles (i.e., [n]cycloparaphenylenes) by the present micelle provides pseudorotaxane-shaped host-guest composites with high emissivity (ΦF=up to 35 %). Internal multi-alkylation of an aromatic micelle can thus successfully enhance its assembly stability/guest uptake functions.

Host-Guest Stimuli-Responsive Click Chemistry

Click chemistry has reached its maturity as the weapon of choice for the irreversible ligation of molecular fragments, with over 20 years of research resulting in the development or improvement of highly efficient kinetically controlled conjugation reactions. Nevertheless, traditional click reactions can be disadvantageous not only in terms of efficiency (side products, slow kinetics, air/water tolerance, etc.), but also because they completely avoid the possibility to reversibly produce and control bound/unbound states. Recently, non-covalent click chemistry has appeared as a more efficient alternative, in particular by using host-guest self-assembled systems of high thermodynamic stability and kinetic lability. This review discusses the implementation of molecular switches in the development of such non-covalent ligation processes, resulting in what we have termed stimuli-responsive click chemistry, in which the bound/unbound constitutional states of the system can be favored by external stimulation, in particular using host-guest complexes. As we exemplify with handpicked selected examples, these supramolecular systems are well suited for the development of human-controlled molecular conjugation, by coupling thermodynamically regulated processes with appropriate temporally resolved extrinsic control mechanisms, thus mimicking nature and advancing our efforts to develop a more function-oriented chemical synthesis.

Synthesis and Inclusion Properties of a β-Cyclodextrin Heptaphosphoramidate

In this study, we report a novel per-6-substituted β-cyclodextrin (4) featuring seven phosphoramidate moieties as an innovative host for inclusion. This structurally well-defined host has remarkable water solubility and was isolated in pure form. Analytical techniques such as NMR and ITC were used to probe the molecular interactions with different drug molecules. Our investigations revealed that host 4 can form 2:1 inclusion complexes with various drugs. Further studies showed that the inclusions of drugs by β-CD host (4) are mostly enthalpy driven, highlighting the potential roles played by the phosphoramidate functionalities of the host. Comparatively, a per-O2, O3-acetylated analog (6) of compound 4 was also obtained, which also shows unusual water solubility but diminished inclusion capability.

Dual catalytic activity of a cucurbit[7]uril-functionalized metal alloy nanocomposite for sustained hydrogen generation: hydrolysis of ammonia borane and electrocatalysts for the hydrogen evolution reaction

H2 is one of the most attractive fuel alternatives to the existing fossil fuels that cause detrimental environmental issues. Thus, there has been an upsurge in the research on the production of green hydrogen. In this view, cucurbit[7]uril (CB7)-functionalized Co:Ni alloy nanocomposites with different compositions, reported here for the first time, were synthesized to synergise the catalytic activities of a nanoalloy and CB7 and screened for hydrogen generation via hydrolysis of ammonia borane (AB). The (Co85:Ni15)50:(CB7)50 nanocomposite exhibited enhanced catalytic performance for AB hydrolysis even at room temperature as compared to the nanoalloy without CB7. Efficient release of ammonia-free green H2 is ensured by the retention of NH3 by the surface functionalized CB7 macrocycles. For sustained release, a novel and cost-effective procedure was used to regenerate AB from the by-product, and the H2 release activity was verified to be on par with commercial AB. The used nanocomposite magnetically separated from the by-product solution was shown to be an efficient electrochemical catalyst for the hydrogen evolution reaction (HER). The cucurbit[7]uril-functionalized Co:Ni nanocomposite demonstrates remarkable dual catalytic performance to generate clean hydrogen from both the hydrolysis of AB at room temperature and the electrochemical HER, thus opening new avenues in supramolecular chemistry for developing noble metal-free catalysts with high activity and long-term stability.

Pillararenes: a new frontier in antimicrobial therapy

Pillararenes have gained great interest among researchers in many fields due to their symmetric structure and facile functionalization. In this review, we summarize recent progress for pillararenes as antimicrobial agents, ranging from cationic pillararenes and peptide-modified pillararenes to sugar-functionalized pillararenes. Moreover, their structure-activity relationships are presented, and their mechanisms of action are discussed. As a state-of-the-art technology, their opportunities and outlook are also outlined in this emerging field. Overall, their potent inhibitory activity and high biocompatibility give them potential for the development of novel antimicrobial agents.

Making the Complicated Simple: A Minimizing Carrier Strategy on Innovative Nanopesticides

The flourishing progress in nanotechnology offers boundless opportunities for agriculture, particularly in the realm of nanopesticides research and development. However, concerns have been raised regarding the human and environmental safety issues stemming from the unrestrained use of non-therapeutic nanomaterials in nanopesticides. It is also important to consider whether the current development strategy of nanopesticides based on nanocarriers can strike a balance between investment and return, and if the complex material composition genuinely improves the efficiency, safety, and circularity of nanopesticides. Herein, we introduced the concept of nanopesticides with minimizing carriers (NMC) prepared through prodrug design and molecular self-assembly emerging as practical tools to address the current limitations, and compared it with nanopesticides employing non-therapeutic nanomaterials as carriers (NNC). We further summarized the current development strategy of NMC and examined potential challenges in its preparation, performance, and production. Overall, we asserted that the development of NMC systems can serve as the innovative driving force catalyzing a green and efficient revolution in nanopesticides, offering a way out of the current predicament.

Intramolecular Cation-π Interactions Organize Bowl-Shaped, Luminescent Molecular Containers

Molecules with nonplanar architectures are highly desirable due to their unique topological structures and functions. We report here the synthesis of two molecular containers (1 ⋅ 3Br- and 1 ⋅ 3Cl-), which utilize intramolecular cation-π interactions to enforce macrocylic arrangements and exhibit high binding affinity and luminescent properties. Remarkably, the geometry of the cation-π interaction can be flexibly tailored to achieve a precise ring arrangement, irrespective of the angle of the noncovalent bonds. Additionally, the C-H⋅⋅⋅Br- hydrogen bonds within the container are also conducive to stabilizing the bowl-shaped conformation. These bowl-shaped conformations were confirmed both in solution through NMR spectroscopy and in the solid state by X-ray studies. 1 ⋅ 3Br- shows high binding affinity and selectivity: F->Cl-, through C-H⋅⋅⋅X- (X=F, Cl) hydrogen bonds. Additionally, these containers exhibited blue fluorescence in solution and yellow room-temperature phosphorescence (RTP) in the solid state. Our findings illustrate the utility of cation-π interactions in designing functional molecules.

Charge-transfer inclusion complex formation of the tropylium cation with prism[6]arenes

Herein, we report that prism[6]arenes (PrS[6]R) can form charge-transfer (CT) inclusion complexes with tropylium tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate (G) in chloroform solution with an obvious CT band at 560 nm. Moreover, the CT complex PrS[6]Et⊃G showed Cl-/Ag+ responsiveness which can be easily monitored by the naked eye.

Bioactive peptide relieves glucocorticoid-induced osteoporosis by giant macrocyclic encapsulation

Bioactive peptides play a crucial role in the field of regenerative medicine and tissue engineering. However, their application in vivo and clinic is hindered by their poor stability, short half-life, and low retention rate. Herein, we propose a novel strategy for encapsulating bioactive peptides using giant macrocycles. Platelet-derived growth factor (PDGF) bioactive mimicking peptide Nap-FFGVRKKP (P) was selected as the representative of a bioactive peptide. Quaterphen[4]arene (4) exhibited extensive host-guest complexation with P, and the binding constant was (1.16 ± 0.10) × 107 M-1. In vitro cell experiments confirmed that P + 4 could promote the proliferation of BMSCs by 2.27 times. Even with the addition of the inhibitor dexamethasone (Dex), P + 4 was still able to save 76.94% of the cells in the control group. Compared to the Dex group, the bone mass of the mice with osteoporosis in the P + 4 group was significantly increased. The mean trabecular thickness (Tb.Th) increased by 17.03%, and the trabecular bone volume fraction (BV/TV) values increased by 40.55%. This supramolecular bioactive peptide delivery strategy provides a general approach for delivering bioactive peptides and opens up new opportunities for the development of peptide-based drugs.

Adamantylglycine as a high-affinity peptide label for membrane transport monitoring and regulation

The non-canonical amino acid adamantylglycine (Ada) is introduced into peptides to allow high-affinity binding to cucurbit[7]uril (CB7). Introduction of Ada into a cell-penetrating peptide (CPP) sequence had minimal influence on the membrane transport, yet enabled up- and down-regulation of the membrane transport activity.

Multi-step FRET systems based on discrete supramolecular assemblies

Fluorescence resonance energy transfer (FRET) from the excited state of the donor to the ground state of the acceptor is one of the most important fluorescence mechanisms and has wide applications in light-harvesting systems, light-mediated therapy, bioimaging, optoelectronic devices, and information security fields. The phenomenon of sequential energy transfer in natural photosynthetic systems provides great inspiration for scientists to make full use of light energy. In recent years, discrete supramolecular assemblies (DSAs) have been successively constructed to incorporate donor and multiple acceptors, and to achieve multi-step FRET between them. This perspective describes recent advances in the fabrication and application of DSAs with multi-step FRET. These DSAs are categorized based on the non-covalent scaffolds, such as amphiphilic nanoparticles, host-guest assemblies, metal-coordination scaffolds, and biomolecular scaffolds. This perspective will also outline opportunities and future challenges in this research area.

Tunable Fluorescence, Morphology, and Antibacterial Behaviors of Conjugated Oligomers via Host-Guest Supramolecular Self-Assembly

Host-guest supramolecular self-assembly has become one facile but efficient way to regulate the optical properties of conjugated oligomers and construct promising photofunctional materials. Herein, we design two linear conjugated oligomers terminated with two or four pyridinium moieties, which show different 1:1 'head-to-tail' binding patterns with cucurbit[8]uril (CB[8]) to form host-guest supramolecules. After being encapsulated in the hydrophobic cavity of the CB[8] host, the fluorescence emission of the conjugated oligomers undergoes significant changes, resulting in tunable fluorescence color with enhanced quantum yields. Triggered by the aggregation of supramolecules, the regular or rigid binding modes lead to the formation of cuboids and spheroids in nanoscale, respectively. Due to the macrocyclic-confinement effect, the light-driven reactive oxygen species (ROS) production of the host-guest complex is increased significantly, thereby improving the photodynamic antibacterial performance toward Staphylococcus aureus (S. aureus).

Peptide recognition by a synthetic receptor at subnanomolar concentrations

This paper describes the discovery and characterization of a dipeptide sequence, Lys-Phe, that binds to the synthetic receptor cucurbit[8]uril (Q8) in neutral aqueous solution with subnanomolar affinity when located at the N-terminus. The thermodynamic and structural basis for the binding of Q8 to a series of four pentapeptides was characterized by isothermal titration calorimetry, NMR spectroscopy, and X-ray crystallography. Submicromolar binding affinity was observed for the peptides Phe-Lys-Gly-Gly-Tyr (FKGGY, 0.3 μM) and Tyr-Leu-Gly-Gly-Gly (YLGGG, 0.2 μM), whereas the corresponding sequence isomers Lys-Phe-Gly-Gly-Tyr (KFGGY, 0.3 nM) and Leu-Tyr-Gly-Gly-Gly (LYGGG, 1.2 nM) bound to Q8 with 1000-fold and 170-fold increases in affinity, respectively. To our knowledge, these are the highest affinities reported between a synthetic receptor and an unmodified peptide. The high-resolution crystal structures of the Q8·Tyr-Leu-Gly-Gly-Gly and Q8·Leu-Tyr-Gly-Gly-Gly complexes have enabled a detailed analysis of the structural determinants for molecular recognition. The high affinity, sequence-selectivity, minimal size of the target binding site, reversibility in the presence of a competitive guest, compatibility with aqueous media, and low toxicity of Q8 should aid in the development of applications involving low concentrations of target polypeptides.

Double-cavity cucurbiturils: synthesis, structures, properties, and applications

Double-cavity Q[n]s are relatively new members of the Q[n] family and have garnered significant interest due to their distinctive structures and novel properties. While they incorporate n glycoluril units, akin to their single-cavity counterparts, their geometry can best be described as resembling a figure-of-eight or a handcuff, distinguishing them from single-cavity Q[n]s. Despite retaining the core molecular recognition traits of single-cavity Q[n]s, these double-cavity variants introduce fascinating new attributes rooted in their distinct configurations. This overview delves into the synthesis, structural attributes, properties, and intriguing applications of double-cavity Q[n]s. Some of the applications explored include their role in supramolecular polymers, molecular machinery, supra-amphiphiles, sensors, artificial light-harvesting systems, and adsorptive separation materials. Upon concluding this review, we discuss potential challenges and avenues for future development and offer valuable insights for other scholars working in this area with the aim of stimulating further exploration and interest.

Pillar[5]arene/albumin biosupramolecular systems for simultaneous native protein preservation and encapsulation of a water-soluble substrate

The growing resistance of pathogens, bacteria, viruses, and fungi to a number of drugs has encouraged researchers to use natural and synthetic biomimetic systems to overcome this challenge. Multicomponent systems are an attractive approach for drug design and multitarget therapy. In this study, we report the assembly of a three-component (pillar[5]arene, bovine serum albumin, and methyl orange) biosupramolecular system as a potential drug delivery system. We estimated the cytotoxic activity and transfection ability of pillar[5]arene derivatives and investigated the effect of the nature of macrocycle functions (L-phenylalanine, glycine, L-alanine) on the native conformation of serum albumin in a three-component system. NMR, UV-vis, fluorescence, CD spectroscopy, DLS, and molecular docking studies were performed in order to confirm the structure and possible pillar[5]arene/bovine serum albumin/methyl orange interactions occurring during the association process. Results indicate that pillar[5]arene with L-phenylalanine fragments retains the native form of BSA to the maximum extent and forms more stable associates.

Supramolecular Switch for the Regulation of Antibacterial Efficacy of Near-Infrared Photosensitizer

The global antibiotic resistance crisis has drawn attention to the development of treatment methods less prone to inducing drug resistance, such as antimicrobial photodynamic therapy (aPDT). However, there is an increasing demand for new photosensitizers capable of efficiently absorbing in the near-infrared (NIR) region, enabling antibacterial treatment in deeper sites. Additionally, advanced strategies need to be developed to avert drug resistance stemming from prolonged exposure. Herein, we have designed a conjugated oligoelectrolyte, namely TTQAd, with a donor-acceptor-donor (D-A-D) backbone, enabling the generation of reactive oxygen species (ROS) under NIR light irradiation, and cationic adamantaneammonium groups on the side chains, enabling the host-guest interaction with curcubit[7]uril (CB7). Due to the amphiphilic nature of TTQAd, it could spontaneously form nanoassemblies in aqueous solution. Upon CB7 treatment, the positive charge of the cationic adamantaneammonium group was largely shielded by CB7, leading to a further aggregation of the nanoassemblies and a reduced antibacterial efficacy of TTQAd. Subsequent treatment with competitor guests enables the release of TTQAd and restores its antibacterial effect. The reversible supramolecular switch for regulating the antibacterial effect offers the potential for the controlled release of active photosensitizers, thereby showing promise in preventing the emergence of drug-resistant bacteria.

Multipurpose new gas chromatography column based on pillararenes functionalized with imidazolium ionic liquids

BACKGROUND

Gas chromatography is worldwide recognized as one of the most important analytical techniques, due to its high versatility and reliability. The heart of a gas chromatograph is the column, that allows analyte peak separations and, consequently, accurate qualitative and qualitative analyses. New and more efficient columns are always requested to satisfy new and challenging analytical needs.

RESULTS

In this work, imidazolium ionic liquids functionalized pillar [5] arenes have been used for the first time as gas chromatographic stationary phases, considering their highly symmetric pillar-shaped architecture with cavities rich in π-electrons. Four imidazolium ionic liquids functionalized pillar [5] arenes have been tested as stationary phases with numerous analytes and isomers. In particular, one of these showed superior performances if compared to commercial columns, enabling challenging isomeric separations of halogenated benzenes, aromatic aldehydes, and aromatic anilines.

SIGNIFICANCE AND NOVELTY

To our knowledge, this is the first report on the use of the ionic liquid P[n]A as a stationary phase in chromatography, either in GC or liquid chromatography (LC) separations. This work demonstrates the promising potential of ionic liquid P[n]A stationary phases for chromatographic separations.

Overcoming barriers with non-covalent interactions: supramolecular recognition of adamantyl cucurbit[n]uril assemblies for medical applications

Adamantane, a staple in medicinal chemistry, recently became a cornerstone of a supramolecular host-guest drug delivery system, ADA/CB[n]. Owing to a good fit between the adamantane cage and the host cavity of the cucurbit[n]uril macrocycle, formed strong inclusion complexes find applications in drug delivery and controlled drug release. Note that the cucurbit[n]uril host is not solely a delivery vehicle of the ADA/CB[n] system but rather influences the bioactivity and bioavailability of drug molecules and can tune drug properties. Namely, as host-guest interactions are capable of changing the intrinsic properties of the guest molecule, inclusion complexes can become more soluble, bioavailable and more resistant to metabolic conditions compared to individual non-complexed molecules. Such synergistic effects have implications for practical bioapplicability of this complex system and provide a new viewpoint to therapy, beyond the traditional single drug molecule approach. By achieving a balance between guest encapsulation and release, the ADA/CB[n] system has also found use beyond just drug delivery, in fields like bioanalytics, sensing assays, bioimaging, etc. Thus, chemosensing in physiological conditions, indicator displacement assays, in vivo diagnostics and hybrid nanostructures are just some recent examples of the ADA/CB[n] applicability, be it for displacements purposes or as cargo vehicles.

Cucurbit[7]uril-mediated Histidine Dimerization: Exploring the Structure and Binding Mechanism

Cucurbit[7,8]urils are known to form inclusion complexes with hydrophobic amino acids such as Trp, Tyr, Phe, and Met, as well as peptides containing these residues at the N-terminus. Despite their widespread use in protein purification, the affinity of histidine (His) for cucurbit[7,8]urils has not been extensively explored. In this study, X-ray diffraction experiments were conducted to investigate the binding of two histidine moieties to the cucurbit[7]uril (CB7) cavity, resulting in a network of π-π and hydrogen bonds. This assembly was found to induce a His pKa shift of ΔpKa=-4. Histidine weakly bound to CB7 or CB8; however, isothermal titration calorimetry revealed micromolar equilibrium dissociation constant values for CB7 and CB8 when bound to dipeptides containing His at the C-terminus. Conversely, dipeptides with His at the N-terminus exhibited millimolar values. Additionally, the His-Gly-Gly tripeptide formed a 2 : 1 complex with CB7. These findings suggest the potential use of histidine and histidine-containing tags in conjunction with CB7 for various biological applications.

Delving into the Variability of Supramolecular Affinity: Self-Ion Pairing as a Central Player in Aqueous Host-Guest Chemistry

The determination of binding constants is a key matter in evaluating the strength of host-guest interactions. However, the profound impact of self-ion pairing on this parameter is often underrated in aqueous solution, leading in some cases to a misinterpretation of the true potential of supramolecular assemblies. In the present study, we aim to shed further light on this critical factor by exploring the concentration-dependent behavior of a multicharged pillararene in water. Our observations reveal an extraordinary 1-million-fold variability in the affinity of this macrocycle toward a given anion, showcasing the highly dynamic character of electrostatic interactions. We argue that these findings bring to the forefront the inherent determinism that underlies the estimation of affinity constants, a factor profoundly shaped by both the sensitivity of the instrumental technique in use and the intricacies of the experimental design itself. In terms of applications, these results may provide the opportunity to optimize the operational concentrations of multicharged hosts in different scenarios, aiming to achieve their maximum efficiency based on the intended application. Unlocking the potential of this hidden variability may pave the way for the creation of novel molecular materials with advanced functionalities.

Highly Stable Organic Molecular Porous Solid Electrolyte with One-Dimensional Ion Migration Channel for Solid-State Lithium-Oxygen Battery

Solid-state lithium-oxygen (Li-O2 ) batteries have been widely recognized as one of the candidates for the next-generation of energy storage batteries. However, the development of solid-state Li-O2 batteries has been hindered by the lack of solid-state electrolyte (SSE) with high ionic conductivity at room temperature, high Li+ transference number, and the high stability to air. Herein, the organic molecular porous solid cucurbit[7]uril (CB[7]) with one-dimensional (1D) ion migration channels is developed as the SSE for solid-state Li-O2 batteries. Taking advantage of the 1D ion migration channel for Li+ conduction, CB[7] SSE achieves high ionic conductivity (2.45 × 10-4 S cm-1 at 25 °C). Moreover, the noncovalent interactions facilitated the immobilization of anions, realizing a high Li+ transference number (tLi + = 0.81) and Li+ uniform distribution. The CB[7] SSE also shows a wide electrochemical stability window of 0-4.65 V and high thermal stability and chemical stability, as well as realizes stable Li+ plating/stripping (more than 1000 h at 0.3 mA cm-2 ). As a result, the CB[7] SSE endows solid-state Li-O2 batteries with superior rate capability and long-term discharge/charge stability (up to 500 h). This design strategy of CB[7] SSE paves the way for stable and efficient solid-state Li-O2 batteries toward practical applications.

Switchable Redox and Thermo-Responsive Supramolecular Polymers Based on Cyclodextrin-Polyoxometalate Tandem

Supramolecular polymers built from stimuli-responsive host-guest interactions represent an attractive way of tailoring smart materials. Herein, we exploit the chaotropic effect of polyoxometalates and related host-guest properties to design unconventional polymer systems with reversible redox and thermo-responsive sol-gel transition. These supramolecular networks result from the association of cyclodextrin-based oligomers and Keggin-type POMs acting as electro-active crosslinking agents. The structure and the dynamics of such self-assembly systems have been investigated using a multiscale approach involving MALDI-TOF, viscosity measurements, cyclic voltammetry, 1 H-NMR (1D and DOSY), and Small-Angle X-ray Scattering. Our results reveal that the chaotropic effect corresponds to a powerful and efficient force that can be used to induce responsiveness in hybrid supramolecular oligomeric systems.

Solution-state mechanochromic luminescence of Pt(ii)-complexes displayed within micellar aromatic capsules

Mechanochromic luminescence (MCL) is an intrinsic phenomenon in the solid state and thus has been hardly observed in solution so far. Here we report that arylethynyl Pt(ii)-complexes with an NCN-pincer ligand are efficiently encapsulated by micellar aromatic capsules in water, through a simple grinding protocol with bent amphiphiles. When a bent pentamethylbenzene-based amphiphile is employed as an optimized capsule component, the resultant host-guest composite, with an average diameter of ∼4 nm, is obtained in water at room temperature. Notably, the nanocomposite displays strong red emission (Φ = 33%, λmax = 700 nm) derived from MCL via intermolecular Pt(ii)⋯Pt(ii) interactions even under aerobic aqueous conditions, in sharp contrast to the free Pt(ii)-complex with weak green emission (Φ = 4%, λmax = 500 nm) in CH2Cl2. Moreover, enhancement of the solution-state MCL (up to Φ = 48%) can be achieved by coencapsulation of the Pt(ii)-complexes with carbazole derivatives by the capsule in water. This study provides the first example of "solution-state" mechanochromic luminescence, capable of facilely tuning its intensity and wavelength, among the intensive studies of various solid-state MCL reported previously.

A High-Affinity "Synthavidin" Receptor for Squaraine Dyes

Strong-binding host-guest pairings in aqueous media have potential as "supramolecular glues" in biomedical techniques, complementing the widely-used (strept)avidin-biotin combination. We have previously found that squaraine dyes are bound very strongly by tetralactam macrocycles possessing anthracenyl units as cavity walls. Here we show that replacing the anthracenes with pentacyclic 5,7,12,14-tetrahydro-5,7,12,14-tetraoxapentacene (TOP) units generates receptors which bind squaraines with increased affinities (around Ka =1010  m-1 ) and improved selectivities. Binding can be followed through changes to squaraine fluorescence and absorbance. The TOP units are easy to prepare and potentially variable, while the TOP-based receptor shows improved photostability, both in itself and in complex with squaraines. The results suggest that this system could prove valuable in the further development of practical "synthavidin" chemistry.

Alignment and Dynamic Inversion of Planar Chirality in Pillar[n]arenes

Pillar[n]arenes are symmetrical macrocyclic compounds composed of benzene panels with para-methylene linkages. Each panel usually exhibits planar chirality and prefers chirality-aligned states. Because of this feature, pillar[n]arenes are attractive scaffolds for chiroptical materials that are easy to prepare and optically resolve and show intense circular dichroism (CD) signals. In addition, rotation of the panels endows the chirality of pillar[n]arenes with a dynamic nature. The chirality in tubular oligomers and supramolecular assemblies sometimes show time- and procedure-dependent alignment phenomena. Furthermore, the CD signals of some pillar[n]arenes respond to the addition of chiral guests when their dynamic chirality is coupled with host-guest properties. By using diastereomeric pillar[n]arenes with additional chiral structures, the response can also be caused by achiral guests and changes of the environment, providing molecular sensors.

Applications of macrocycle-based solid-state host-guest chemistry

Macrocyclic molecules have been used in various fields owing to their guest binding properties. Macrocycle-based host-guest chemistry in solution can allow for precise control of complex formation. Although solution-phase host-guest complexes are easily prepared, their limited stability and processability prevent widespread application. Extending host-guest chemistry from solution to the solid state results in complexes that are generally more robust, enabling easier processing and broadened applications. Macrocyclic compounds in the solid state can encapsulate guests with larger affinities than their soluble counterparts. This is crucial for use in applications such as separation science and devices. In this Review, we summarize recent progress in macrocycle-based solid-state host-guest chemistry and discuss the basic physical chemistry of these complexes. Representative macrocycles and their solid-state complexes are explored, as well as potential applications. Finally, perspectives and challenges are discussed.

Challenges and Opportunities of Functionalized Cucurbiturils for Biomedical Applications

Cucurbit[n]uril (CB[n]) macrocycles (especially CB[5] to CB[8]) have shown exceptional attributes since their discovery in 2000. Their stability, water solubility, responsiveness to several stimuli, and remarkable binding properties have enabled a growing number of biological applications. Yet, soon after their discovery, the challenge of their functionalization was set. Nevertheless, after more than two decades, a myriad of CB[n] derivatives has been described, many of them used in cells or in vivo for advanced applications. This perspective summarizes key advances of this burgeoning field and points to the next opportunities and remaining challenges to fully express the potential of these fascinating macrocycles in biology and biomedical sciences.

A Redox-Responsive Ferrocene-Based Capsule Displaying Unusual Encapsulation-Induced Charge-Transfer Interactions

A ferrocene-based capsule is spontaneously and quantitatively formed in water by the assembly of bent amphiphiles carrying two ferrocene units. The disassembly and assembly of the new organometallic capsule, with a well-defined and highly condensed ferrocene core, are demonstrated by chemical redox stimuli in a fully reversible fashion under ambient conditions. In contrast to previously reported multiferrocene assemblies, only the present capsule efficiently encapsulates typical organic/inorganic dyes as well as electron-accepting molecules in water. As a result, unusual host-guest charge-transfer (CT) interactions, displaying relatively wide absorption bands in the visible to near-infrared region (λ=650-1350 nm), are observed upon the encapsulation of acceptors (i.e., chloranil and TCNQ). The resultant encapsulation-induced CT interactions can be released by a redox stimulus through the disassembly of the capsule.

Synthesis of a water-soluble naphthalene-based macrocycle and its host-guest properties

Reported here is the synthesis of a naphthalene-based macrocycle bearing anionic carboxylato groups on the rims along with its complexation with cationic guests in aqueous media. The macrocycle could strongly bind guests in a molecular clip model with association constants of 106-107 M-1.

Potential of nonporous adaptive crystals for hydrocarbon separation

Hydrocarbon separation is an important process in the field of petrochemical industry, which provides a variety of raw materials for industrial production and a strong support for the development of national economy. However, traditional separation processes involve huge energy consumption. Adsorptive separation based on nonporous adaptive crystal (NAC) materials is considered as an attractive green alternative to traditional energy-intensive separation technologies due to its advantages of low energy consumption, high chemical and thermal stability, excellent selective adsorption and separation performance, and outstanding recyclability. Considering the exceptional potential of NAC materials for hydrocarbon separation, this review comprehensively summarizes recent advances in various supramolecular host-based NACs. Moreover, the current challenges and future directions are illustrated in detail. It is expected that this review will provide useful and timely references for researchers in this area. Based on a large number of state-of-the-art studies, the review will definitely advance the development of NAC materials for hydrocarbon separation and stimulate more interesting studies in related fields.

Small-molecule probes from bench to bedside: advancing molecular analysis of drug-target interactions toward precision medicine

Over the past decade, remarkable advances have been witnessed in the development of small-molecule probes. These molecular tools have been widely applied for interrogating proteins, pathways and drug-target interactions in preclinical research. While novel structures and designs are commonly explored in probe development, the clinical translation of small-molecule probes remains limited, primarily due to safety and regulatory considerations. Recent synergistic developments - interfacing novel chemical probes with complementary analytical technologies - have introduced and expedited diverse biomedical opportunities to molecularly characterize targeted drug interactions directly in the human body or through accessible clinical specimens (e.g., blood and ascites fluid). These integrated developments thus offer unprecedented opportunities for drug development, disease diagnostics and treatment monitoring. In this review, we discuss recent advances in the structure and design of small-molecule probes with novel functionalities and the integrated development with imaging, proteomics and other emerging technologies. We further highlight recent applications of integrated small-molecule technologies for the molecular analysis of drug-target interactions, including translational applications and emerging opportunities for whole-body imaging, tissue-based measurement and blood-based analysis.

Unimolecular Chiral Stepping Inversion Machine

Intelligent molecular machines that are driven by light, electricity, and temperature have attracted considerable interest in the fields of chemistry, materials, and biology. Herein, a unimolecular chiral stepping inversion molecular machine (SIMM) was constructed by a coupling reaction between dibromo pillar[5]arene and a tetrathiafulvalene (TTF) derivative (PT3 and PT5). Compared with the longer aliphatic linker PT5, PT3 with a shorter aliphatic linker shows chiral stepping inversion, achieving chiral inversion under a two-electron redox potential. Benefiting from the successive reversible two-electron redox potential of TTF, the self-exclusion and self-inclusion conformational transformations of SIMM can proceed in two steps under redox, leading to the chirality step inversion in the pillar[5]arene core. Electrochemical experiments and circular dichroism (CD) spectra show that the redox processes can cause SIMM CD signaling to reversibly switch. More importantly, as the oxidant Fe(ClO₄)₃ was increased from 0.1 to 1 equiv, the CD spectral signal of SIMM disappeared at 1 equiv, and further addition of Fe(ClO₄)₃ resulted in the CD signal reversed from positive to negative at 309 nm, indicating that the chirality was reversed after chemical oxidation and reached a negative maximum with the addition of 2 equiv Fe(ClO₄)₃; thus, redox-triggered chiral stepping inversion was achieved. Furthermore, the chiral inversion can be restored to its original state after the addition of 2 equiv of reducing agent, sodium ascorbate. This work demonstrates unimolecular chiral stepping inversion, providing a new perspective on stimulus-responsive chirality in molecular machines.

Control of reactivity and selectivity in isomerization and rearrangement reactions inside confined spaces

In the confined space of supramolecular systems, the substrate can be forced into a reactive conformation and labile intermediates may be stabilized while isolated from the bulk solution. In this highlight, unusual processes mediated by supramolecular hosts are described. These include unfavourable conformational equilibria, unusual product selectivities in bond and ring-chain isomerizations, accelerated rearrangement reactions through labile intermediates, and encapsulated oxidations. In the host, controlled or altered isomerization of the guests can occur via hydrophobic, photochemical and thermal interventions. The inner spaces of the hosts resemble enzyme cavities that stabilize labile intermediates not accessible in the bulk solvent. The effects of confinement and the binding forces involved are discussed and further applications are suggested.

Electrochemical Detection of Drugs via a Supramolecular Cucurbit[7]uril-Based Indicator Displacement Assay

Electrochemical detection methods are attractive for developing miniaturized, disposable, and portable sensors for molecular diagnostics. In this article, we present a cucurbit[7]uril-based chemosensor with an electrochemical signal readout for the micromolar detection of the muscle relaxant pancuronium bromide in buffer and human urine. This is possible through a competitive binding assay using a chemosensor ensemble consisting of cucurbit[7]uril as the host and an electrochemically active platinum(II) compound as the guest indicator. The electrochemical properties of the indicator are strongly modulated depending on the complexation state, a feature that is exploited to establish a functional chemosensor. Our design avoids cumbersome immobilization approaches on electrode surfaces, which are associated with practical and conceptual drawbacks. Moreover, it can be used with commercially available screen-printed electrodes that require minimal sample volume. The design principle presented here can be applied to other cucurbit[n]uril-based chemosensors, providing an alternative to fluorescence-based assays.

Aqueous Three-Component Self-Assembly of a Pseudo[1]rotaxane Using Hydrazone Bonds

We present herein the synthesis of a new polycationic pseudo[1]rotaxane, self-assembled in excellent yield through hydrazone bonds in aqueous media of three different aldehyde and hydrazine building blocks. A thermodynamically controlled process has been studied sequentially by analyzing the [1 + 1] reaction of a bisaldehyde and a trishydrazine leading to the macrocyclic part of the system, the ability of this species to act as a molecular receptor, the conversion of a hydrazine-pending cyclophane into the pseudo[1]rotaxane and, lastly, the one-pot [1 + 1 + 1] condensation process. The latter was found to smoothly produce the target molecule through an integrative social self-sorting process, a species that was found to behave in water as a discrete self-inclusion complex below 2.5 mM concentration and to form supramolecular aggregates in the 2.5-70 mM range. Furthermore, we demonstrate how the abnormal kinetic stability of the hydrazone bonds on the macrocycle annulus can be advantageously used for the conversion of the obtained pseudo[1]rotaxane into other exo-functionalized macrocyclic species.

Water soluble macrocyclic host for recognition of N-methylquinolinium salts in water

In this paper, we reported the synthesis of water soluble macrocyclic arenes 1 containing anionic carboxylate groups. It was found that host 1 could form a 1 : 1 complex with N-methylquinolinium salts in water. Moreover, the complexation and decomplexation of the complexes between host and the guests could be achieved by changing the pH of the solution, and the process could also be observed by naked eye.

Pillar[6]MaxQ: A Potent Supramolecular Host for In Vivo Sequestration of Methamphetamine and Fentanyl

Pillar[6]MaxQ (P6AS) functions as an in vivo sequestration agent for methamphetamine and fentanyl. We use 1H NMR, isothermal titration calorimetry, and molecular modelling to deduce the geometry and strength of the P6AS•drug complexes. P6AS forms tight complexes with fentanyl (Kd=9.8 nM), PCP (17.1 nM), MDMA (25.5 nM), mephedrone (52.4 nM), and methamphetamine (101 nM). P6AS has good in vitro biocompatibility according to MTS metabolic, Adenylate Kinase cell death, and hERG ion channel inhibition assays, and the Ames fluctuation test. The no observed adverse effect level for P6AS is 45 mg/kg. The hyperlocomotion of mice treated with methamphetamine (0.5 mg/kg) can be ameliorated by treatment with P6AS (35.7 mg/kg) 5-minutes later, whereas the hyperlocomotion of mice treated with fentanyl (0.1 mg/kg) can be controlled by treatment with P6AS (5 mg/kg) up to 15-minutes later. P6AS has significant potential for development as a broad spectrum in vivo sequestration agent.

Stimuli-responsive mechanically interlocked molecules constructed from cucurbit[n]uril homologues and derivatives

Cucurbit[n]uril supramolecular chemistry has developed rapidly since 2001 when different cucurbit[n]uril homologues (Q[n]) were successfully separated in pure form. The combination of Q[n] cavity size and various types of external stimuli has given birth to numerous types of Q[n]-based mechanically interlocked molecules (MIMs), including (pseudo)rotaxanes, catenanes, dendrimers and poly(pseudo)rotaxanes. In this review article, the important advances in the field of Q[n]-based MIMs over the past two decades are highlighted. This review also describes examples of heterowheel (pseudo)rotaxanes and poly(pseudo)rotaxanes involving Q[n]s, and reflects on the opportunities and challenges of constructing Q[n]-based stimuli-responsive MIMs.