Tunable Nanosupramolecular Aggregates Mediated by Host-Guest Complexation

Nanoaggregation-Enhanced and Inverted Circularly Polarized Luminescence in Isomeric Schiff Base Bis(boron difluoride) Complexes

To elucidate the emergence and amplification of circularly polarized luminescence (CPL) in chiral molecules and their assemblies, we designed positionally isomeric chiral V-shaped Schiff base ligands and their corresponding bis(boron difluoride) complexes. The ligands were synthesized by condensing chiral cyclohexanediamine with either 1-hydroxy-2-naphthaldehyde or 2-hydroxy-1-naphthaldehyde, followed by complexation with boron difluoride (BF2) to yield CNB1 and CNB2, respectively. While the parent Schiff bases exhibited no CPL, BF2 coordination induced strong CPL signals in solution. Remarkably, upon aggregation in a mixed solvent system, CNB2 displayed enhanced and inverted CPL, whereas its isomer CNB1 showed attenuated emission. Through comprehensive characterization and singlecrystal analysis, we attribute this divergent behavior to distinct molecular packing modes: CNB2 forms tightly stacked aggregates with efficient π─π interactions, while CNB1 adopts a less ordered arrangement. This study establishes a clear correlation between subtle structural modifications, supramolecular packing, and CPL performance, offering a rational strategy for tailoring chiroptical properties through precise molecular design and controlled self-assembly.

Tailored Nucleation-Growth Strategy for Precise Self-Assembly of Block Copolymers

The self-assembly of block copolymers (BCPs) to form nanostructures of various morphologies and controllable dimensions has been a very promising research area in nanotechnology in recent decades. This concept mainly summarizes the recent advances in precise and controllable self-assembly of BCPs through a tailored nucleation-growth strategy to modulate the self-assembly behavior of the BCPs. These efforts have led to a better understanding of the self-assembly mechanisms and opened new possibilities for creating novel materials with designable properties. We hope that the concept is more than a periodical summary of previous research work and can provide valuable inspiration for the research field.

Sensitive detection of α-amylase based on host-guest inclusion system of γ-cyclodextrin and dansyl-derived diphenylalanine

A highly sensitive detection system for α-amylase was developed via host-guest complexation between γ-cyclodextrin and dansyl-modified diphenylalanine (FF-Dns). The host-guest inclusion of FF-Dns into the cavity of γ-CD in a HEPES buffer solution (10 mM, pH 7.4) significantly enhanced the fluorescence intensity, and the emission wavelength gradually shifted from 558 to 535 nm. The hydrolysis of γ-CD by the addition of α-amylase released FF-Dns, leading to the recovery of the fluorescence emission characteristics. Therefore, the FF-Dns/γ-CD host-guest complexation system can serve as a platform for the sensitive detection of α-amylase with good selectivity against potential interference. The limit of detection (LOD) of the system was 0.004 U/mL, with a linear working range of 0-6 U/mL. The detection assay was successfully applied in 0.1 % serum, achieving an LOD of 0.017 U/mL and a linear working range of 0-10 U/mL.

Aggression to Biomembranes by Hydrophobic Tail Chains under the Stimulus of Reductant

Stimulus-responsive materials hold significant promise for antitumor applications due to their variable structures and physical properties. In this paper, a series of peptides with a responsive viologen derivative, Pep-CnV (n = 1, 2, 3) were designed and synthesized. The process and mechanism of the interaction were studied and discussed. An ultraviolet-visible (UV) spectrophotometer and fluorescence spectrophotometer were used to study their redox responsiveness. Additionally, their secondary structures were measured by Circular Dichroism (CD) in the presence or absence of the reductant, Na2SO3. DPPC and DPPG liposomes were prepared to mimic normal and tumor cell membranes. The interaction between Pep-CnV and biomembranes was investigated by the measurements of surface tension and cargo leakage. Results proved Pep-CnV was more likely to interact with the DPPG liposome and destroy its biomembrane under the stimulus of the reductant. And the destruction increased with the length of the hydrophobic tail chain. Pep-CnV showed its potential as an intelligent antitumor agent.

Photo-controlled order-to-order host-guest self-assembly transfer for an afterglow effect with water resistance

Due to the general incompleteness of photochemical reactions, the photostationary structure in traditional photo-controlled host-guest self-assembly transfer is usually disordered or irregular. This fact readily affects the photoregulation or improvement of related material properties. Herein, a photoexcitation-induced aggregation molecule, hydroxyl hexa(thioaryl)benzene (HB), was grafted into β-cyclodextrin to form a host-guest system. Upon irradiation, the excited state conformational change of HB can drive an order-to-order phase transition of the system, enabling the transfer of the initial linear nanostructure to a photostationary worm-like nanostructure with orderliness and crystallinity capability. Along with the photoexcitation-controlled phase transition, an afterglow effect was obtained from the films prepared by doping the host-guest system into poly(vinyl alcohol). The afterglow effect had a superior water resistance, which successfully overcame the general sensitivity of doped materials with the afterglow effect to water vapor. These results are expected to provide new insights for pushing forward chemical self-assembly from the light perspective, towards materials with superior and stable properties under light treatment.

Cucurbituril-based supramolecular host-guest complexes: single-crystal structures and dual-state fluorescence enhancement

Two supramolecular complexes were prepared using cucurbiturils [CBs] as mediators and a four-armed p-xylene derivative (M1) as a guest molecule. The single crystals of these two complexes were obtained and successfully analyzed by single-crystal X-ray diffraction (SCXRD). An unexpected and intriguing 1 : 2 self-assembly arrangement between M1 and CB[8] was notably uncovered, marking its first observation. These host-guest complexes exhibit distinctive photophysical properties, especially emission behaviors. Invaluable insights can be derived from these single-crystal structures. The precious single-crystal structures provide both precise structural information regarding the supramolecular complexes and a deeper understanding of the intricate mechanisms governing their photophysical properties.

Photocontrolled Reversibly Chiral-Ordered Assembly Based on Cucurbituril

Chirality transfer and regulation, accompanied by morphology transformation, arouse widespread interest for application in materials and biological science. Here, a photocontrolled supramolecular chiral switch is fabricated from chiral diphenylalanine (l-Phe-l-Phe, FF) modified with naphthalene (2), achiral dithienylethene (DTE) photoswitch (1), and cucurbit[8]uril (CB[8]). Chirality transfer from the chiral FF moiety of 2 to a charge-transfer (CT) heterodimer consisting of achiral guest 1 and achiral naphthalene (NP) in 2 has been unprecedented achieved via the encapsulation of CB[8]. On the contrary, chirality transfer from chiral FF to NP cannot be conducted in only guest 2. Crucially, induced circular dichroism of the heterodimer can be further modulated by distinct light, attributing to reversible photoisomerization of the DTE. Meanwhile, topological nanostructures are changed from one-dimensional (1D) nanofibers to two-dimensional (2D) nanosheets in the orderly assembling process of the heterodimer, which further achieved reversible interconversion between 2D nanosheets and 1D nanorods with tunable-induced chirality stimulated by diverse light.

Enhanced molecular binding affinity toward aromatic dications by anthracene-derived crown ethers in water

The pursuit of high molecular binding affinity using conventional crown ethers in water remains a challenging task in the field of supramolecular chemistry and may hold great promise in the creation of advanced biocompatible nanoconstructs. In this work, the molecular binding strength toward a series of structurally relevant cationic guests has been greatly enhanced by tetrasulfonated 1,5-dianthracenyl-42-crown-10 and as investigated by means of ¹H NMR, UV-vis, and fluorescence spectroscopy, the host-guest association constants can reach up to 10⁸ M^-1 order of magnitude in aqueous solution. X-ray crystal diffraction analysis further demonstrates that the aromatic dication can be tightly encapsulated in the ring of anthracene-derived crown ether via multiple π-stacking and electrostatic interactions. Meanwhile, the obtained association constants are remarkably higher than the ones in the cases of the known benzene- and naphthalene-derived sulfonated crown ethers, substantiating that the appropriate extension of π-conjugation in the molecular skeleton of crown ether is a feasible method in attaining a highly affiliative host-guest complex. Taken together, our results indicate that the anthracene-based sulfonated crown ether can be developed as a new family of water-soluble macrocyclic receptors in the fabrication of functional nanoarchitectures.

Bioinspired Supramolecular Nanotoroids with Aggregation-Induced Emission Characteristics

Supramolecular toroids have attracted continuous attention because of their fascinating topological structure and important role in biological systems. However, it still remains a great challenge to construct supramolecular functional toroids and clarify the formation mechanism. Herein, we develop a strategy to prepare supramolecular helical fluorescent nanotoroids by cooperative self-assembly of an amino acid and a dendritic amphiphile (AIE-den-1) with aggregation-induced emission characteristics. Mechanistic investigation on the basis of fluorescence and circular dichroism analyses suggests that the toroid formation can be driven by the interactions of AIE-den-1 with amino acid and goes through a topological morphology transformation from nanofibers to left-handed nanotoroids by means of a twist-fused-loop process.

Hybrid Macrocyclic Polymers: Self-Assembly Containing Cucurbit[m]uril-pillar[n]arene

Supramolecular self-assembly by hybrid macrocycles containing both cucurbit[m]uril (CB[m]) and pillar[n]arene was discussed and summarized in this review. Due to different solubility, diverse-sized cavities, and various driving forces in recognizing guests, the role of CB[m] and pillar[n]arene in such hybrid macrocyclic systems could switch between competitor in capturing specialized guests, and cooperator for building advanced hybridized macrocycles, by controlling their characteristics in host-guest inclusions. Furthermore, both CB[m] and pillar[n]arene were employed for fabricating advanced supramolecular self-assemblies such as mechanically interlocked molecules and supramolecular polymers. In those self-assemblies, CB[m] and pillar[n]arene played significant roles in, e.g., microreactor for catalyzing particular reactions to bridge different small pieces together, molecular "joint" to connect different monomers into larger assemblies, and "stabilizer" in accommodating the guest molecules to adopt a favorite structure geometry ready for assembling.

Single-crystal structures of cucurbituril-based supramolecular host-guest complexes for bioimaging

Two single-crystal structures of cucurbit[n]uril mediated supramolecular complexes were obtained in which [1+3] and [2+3] self-assembly modes are adopted due to the different sizes of cucurbit[7]uril and cucurbit[8]uril. An obvious red-shift in absorption and emission was observed compared to the guest molecule itself which makes them good biolabels.

Cucurbituril-activated photoreaction of dithienylethene for controllable targeted lysosomal imaging and anti-counterfeiting

Supramolecular macrocycle-mediated photoreaction has been a research hotspot recently. Herein, we fabricated a photo-responsive intelligent supramolecular assembly that consisted of a water-soluble dithienylethene derivative (DTE-MPBT) and cucurbit[n]urils (CB[n]). Importantly, CB[n], especially CB[8], could act as activators and trigger conformational alteration of the arm parts (typical molecular rotors) of DTE-MPBT, achieving dual functions, i.e. high-efficiency visible-light-cyclization reaction of the DTE core and fluorescence enhancement of DTE-MPBT, resulting in the formation of a dual visible light-driven fluorescent switch. These unexpected discoveries prompted the supramolecular assembly to be applied to dual-visible-light-controlled targeted lysosomal imaging and QR code information recognition. Moreover, the solid-state assembly exhibited more outstanding fluorescence and visible-light-switched fluorescence performance because of the host-guest-induced aggregation synergistic effect, showing fascinating applications, such as light-manipulative data storage and anti-counterfeiting. In brief, we unprecedentedly adopted a supramolecular strategy of "killing two birds with one stone", i.e. assembly-activated photochromism (AAP) and assembly-activated emission enhancement (AAEE), to fabricate dual-visible-light-driven fluorescent switches, which show promising application prospects in biomimetic smart nanomaterials based on supramolecular self-assembly systems.

Tunable Supramolecular Nanoarchitectures Constructed by the Complexation of Diphenanthro-24-Crown-8/Cesium(I) with Nickel(II) and Silver(I) Ions

Tunable supramolecular nanoarchitectures have received enormous attention because of their potential in materials fabrication. Herein, a variety of morphologically intriguing nanoarchitectures have been constructed from diphenanthro-24-crown-8 ether (DPC) and metal ions. SEM and TEM showed that the self-assembled nanofibers undergo a Cs^I -induced transformation into regular nanoribbons, and further into nanospheres and nanoparticles by the complexation of Ni^II and Ag^I ions because of the strong ion-dipole interaction. Moreover, the X-ray crystal structure determination and powder X-diffraction data further confirmed that these morphological transformations resulted from the different complexation between DPC and metal ions. This result provides a new strategy for the subtle manipulation of supramolecular assemblies.

Highly efficient photocontrolled targeted delivery of siRNA by a cyclodextrin-based supramolecular nanoassembly

A binary supramolecular nanoassembly that can efficiently load siRNA into A549 cancer cells and inhibited cell growth by photo-irradiation was fabricated using α-CD-modified hyaluronic acid and an azobenzene-modified diphenylalanine derivative.

Self-Healing and Recyclable Hydrogels Reinforced with in Situ-Formed Organic Nanofibrils Exhibit Simultaneously Enhanced Mechanical Strength and Stretchability

In this work, self-healing and recyclable polymer hydrogels with simultaneously enhanced mechanical strength and stretchability are fabricated through the complexation of poly(acrylic acid) (PAA) with complexes of branched poly(ethylenimine) and 1-pyrenybutyric acid (PEI-PYA) to generate PAA/PEI-PYA complexes, which are further molded, dried, and rehydrated. The in situ-formed PYA nanofibrils with aggregated structures during the complexation process enable the simultaneous enhancement of the tensile strength and stretchability of the PAA/PEI-PYA hydrogels. The PAA/PEI-PYA hydrogels have a tensile strength of 1.13 ± 0.04 MPa and stretchability of 2970 ± 154%, which are 2.2 and 2.1 times higher than those of the PAA/PEI hydrogels. Meanwhile, the damaged PAA/PEI-PYA hydrogels can be efficiently healed or recycled at room temperature to regain their original mechanical strength and integrity because the dynamic nature of hydrogen-bonding and electrostatic interactions among PAA, PEI, and PYA endows the hydrogels with excellent healing and recycling capacity. This strategy of using aggregated nanofibrils to simultaneously enhance the tensile strength and stretchability of hydrogels can be extended to PAA/PEI hydrogels reinforced with aggregated nanofibrils of 9-anthracenecarboxylic acid and N,N'-di(propanoic acid)-perylene-3,4,9,10-tetracarboxylic diimide, demonstrating its generality for fabricating hydrogels with enhanced mechanical properties.

Pd-catalyzed asymmetric allylic substitution cascade using α-(pyridin-1-yl)-acetamides formed in situ as nucleophiles

A Pd-catalyzed asymmetric allylic substitution cascade reaction, using α-(pyridin-1-yl)-acetamides (formed in situ) as nucleophiles, has been developed, generating chiral piperidine-containing amino acid derivatives via a one-pot procedure in high yields and with up to 96% ee. The products can be easily converted into potential bioactive compounds, unnatural chiral amino acids and dipeptides.

Water-Soluble Pillar[n]arene Mediated Supramolecular Self-Assembly: Multi-Dimensional Morphology Controlled by Host Size

We report tunable supramolecular self-assemblies formed by water-soluble pillar[n]arenes (WPns, n=5-7) and bipyridinium-azobenzene guests. Nanoscale or microscale morphology of self-assemblies in water was controlled by the host size of WPn. Supramolecular self-assemblies could undergo morphology conversion under irradiation with UV light.

Effect of scaffold structures on the artificial light-harvesting systems: a case study with an AIEE-active pillar[5]arene dyad

The presence of a supramolecular polymeric scaffold structure enhanced the energy transfer capacity of the artificial light-harvesting nanoparticles.

Preparation of cross-linked supramolecular polymers based on benzo-21-crown-7/secondary ammonium salt host-guest interactions

We found that TC7 not only self-assembles into one-dimensional supramolecular aggregates in chloroform, but also forms cross-linked supramolecular polymers via host-guest complexation between benzo-21-crown-7 and secondary ammonium salts. Compared with one-dimensional linear supramolecular polymers, soft and long viscous fibers were pulled out from a concentrated solution of cross-linked supramolecular polymers as a result of higher viscosity and lower diffusion coefficients.

Construction of Crowning β-cyclodextrin with Temperature Response and Efficient Properties of Host-Guest Inclusion

Promoting a drug inclusion proportion in hydrophobic cavity of β-cyclodextrin using simple methods is a highly ambitious task. Herein, we report the crowning β-cyclodextrins formed by intramolecular hydrogen bonding interaction, which has greatly prolonged the cavity depth of β-cyclodextrin, and therefore further efficiently improved the inclusion proportion to complex drug molecule (vitamin E). Furthermore, the self-assembly behaviors, controllable release, and antioxidant properties of vitamin E embedded into the cavity of crowning β-cyclodextrins was investigated, and host-guest inclusions exhibited temperature-responsive controlled release, excellent antioxidant activity, and photostability.

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.

2:2 Complexes from Diphenylpyridiniums and Cucurbit[8]uril: Encapsulation-Promoted Dimerization of Electrostatically Repulsing Pyridiniums

Rigid linear compounds G1 and G2, which contained two 4-phenylpyridinium (PhPy⁺ ) units, have been prepared to investigate their binding with cucurbit[8]uril (CB[8]). X-ray crystallographic structures revealed that in the solid state both compounds were included by CB[8], through antiparallel stacking, to form 2:2 quaternary complexes (G1)₂ @(CB[8])₂ and (G2)₂ @(CB[8])₂ . For the former complex, CB[8] entrapped G1 by holding two heterodimers of its Py⁺ and benzyl units, which were at opposite ends of the backbone. In contrast, for the first time, the second complex disclosed parallel stacking of two cationic Py⁺ units of G2 in the cavity of CB[8] in the solid state, despite the generation of important electrostatic repulsion. Isothermal titrations in water afforded high apparent association constants of 4.36×10⁶ and 6.43×10⁶  m^-1 for 1:1 complexes G1@CB[8] and G2@CB[8], respectively, and ¹ H NMR spectroscopy experiments in D₂ O confirmed a similar stacking pattern to that observed in the solid state. A previous study and crystal structures of the 2:1 complexes formed between three new controls, G3-5, and CB[8] did not display such unusual stacking of the cationic Py⁺ unit; this may be attributed to the multivalency of the two CB[8] encapsulation interactions.

A hyaluronidase/temperature dual-responsive supramolecular assembly based on the anionic recognition of calixpyridinium

We have successfully constructed a supramolecular assembly based on the anionic recognition of calixpyridinium for the first time employing native biocompatible polysaccharide hyaluronan as the guest, which showed hyaluronidase-responsive disassembly and temperature-responsive morphological conversion from a nanosphere to a nanosquare upon increasing the temperature.

Tunable fluorescence behaviors of a supramolecular system based on a fluorene derivative and cucurbit[8]uril and its application for ATP sensing

In this work, we developed a supramolecular fluorescent system based on host-guest interactions between a fluorene derivative carrying two bispyridinium units (FPy) and cucurbit[8]uril (CB[8]). In aqueous solution, the system showed outstanding tunable emission properties. After being encapsulated into the rigid hydrophobic cavity of the CB[8] host, the fluorescence emission of fluorene had an obvious red-shift with enhanced quantum yield. Interestingly, the emission behavior of the FPy/CB[8] complex showed a two-step self-assembly process when the molar ratio of FPy to CB[8] changed from 1 : 1 to 1 : 2. Besides, the influence of several factors on the emission properties of the FPy/CB[8] complex was also investigated, like pH value, salt concentration, and temperature. Finally, the fluorescent FPy/CB[8] complexes displayed a good performance for detection of adenosine-5'-triphosphate (ATP), which can cause aggregation-induced quenching of the complexes via electrostatic attraction.

Nanotrumpets and circularly polarized luminescent nanotwists hierarchically self-assembled from an achiralC3-symmetric ester

An achiralC₃-symmetric molecule was found to self-assemble into various hierarchical nanostructures such as nanotwists, nanotrumpets and nanobelts, in which the twisted fibers showed supramolecular chirality as well as circularly polarized luminescence although the compound is achiral.

Photocontrolled reversible conversion of a lamellar supramolecular assembly based on cucurbiturils and a naphthalenediimide derivative

Lamellar and helical supramolecular assemblies were constructed using cucurbiturils and a naphthalenediimide derivative. The formation of the lamellar assembly could be reversibly photocontrolled.

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.

Construction of protein assemblies by host–guest interactions with cucurbiturils

Protein assembly is important in nature and bionics. Herein, we have reviewed the recent progress in protein assemblies induced by cucurbituril-based supramolecular interactions and their applications.

End-to-end assembly and disassembly of gold nanorods based on photo-responsive host–guest interaction

The end-to-end assembly and disassembly of gold nanorods were realized via HS-β-CD recognition and controllable by both UV light irradiation and guest competition.

Effects of side chains of oxatub[4]arene on its conformational interconversion, molecular recognition and macroscopic self-assembly

The side-chain length of oxatub[4]arenes was shown to affect its conformational interconversion, molecular recognition and macroscopic self-assembly behavior.