Dual‐Stimuli Responsive 2D Supramolecular Organic Framework for the Detection of Azoreductase Activity

White-Light Emission from a Host-Guest Composite between Carboxylatopillar[5]arene-Modified N-Doped Carbon Dots and Rhodamine 6G for Rutin Detection

The construction of tunable white-light-emitting materials has garnered increasing attention in the scientific community. In this study, N-doped carbon dots (N-CDs) were surface-modified with carboxylatopillar[5]arene (CP[5]) using an EDC-NHS coupling reaction to create CCDs. CCDs were then conjugated with rhodamine 6G (R6G) through host-guest interactions to fabricate the CCDs-R6G composites. These composites produced two-color fluorescence emission peaks at 447 and 557 nm when excited by a wavelength of 340 nm. Excitingly, white-light emission (0.28, 0.30) can be readily achieved by varying the R6G concentration. To further explore potential applications, a new detection method for rutin (RT) based on the inner filter effect (IFE) was developed. Experimental results verify the practicality and reliability of the fluorescence sensor based on CCDs-R6G composites for RT detection in real samples.

Emerging sensing platforms based on Cucurbit[n]uril functionalized gold nanoparticles and electrodes

Cucurbit[n]urils (CB[n]s, n = 5-8, 10, and 14), synthetic macrocycles with unique host-guest properties, have triggered increasing research interest in recent years. Gold nanoparticles (Au NPs) and electrodes stand out as exceptional substrates for sensing due to their remarkable physicochemical characteristics. Coupling the CB[n]s with Au NPs and electrodes has enabled the development of emerging sensing platforms for various promising applications. However, monitoring the behavior of analytes at the single-molecule level is currently one of the most challenging topics in the field of CB[n]-based sensing. Constructing supramolecular junctions in a sensing platform provides an ideal structure for single-molecule analysis, which can provide insights for a fundamental understanding of supramolecular interactions and chemical reactions and guide the design of sensing applications. This feature article outlines the progress in the preparation of the CB[n] functionalized Au NPs and Au electrodes, as well as the construction and application of supramolecular junctions in sensing platforms, based on the methods of recognition tunneling (RT), surface-enhanced Raman spectroscopy (SERS), single-molecule force spectroscopy (SMFS), and electrochemical sensing (ECS). A brief perspective on the future development of and challenges in CB[n] mediated sensing platforms is also covered.

A multifunctional supramolecular assembly based on cucurbit[7]uril: White light material and Fe(CN)63- detection

White light emitting materials have broad application prospects in fields such as displays, lighting devices, etc., but developing such materials faces considerable challenges. In this study, 1,3,5-tris[4-(pyridine-4-butyl)phenyl]benzene derivative (BTPY) was synthesized and a supramolecular assembly with AIE properties named BTPY@Q[7] was prepared with cucurbit[7]uril (Q[7]). Furthermore, by adding rhodamine 6G (R6G) to it, and controlling its ratio with R6G, a dual-emission white light system (0.33, 0.33) was synthesized and used for white light emitting materials as well as anti-counterfeiting fields. In addition, based on the BTPY@Q[7]-R6G system, a light harvesting system in aqueous phase was constructed, with an energy transfer efficiency (ΦET) of 26.19 % and an antenna effect (AE) of 10.21. Interestingly, the supramolecular self-assembly can also be used as a fluorescent probe, specifically recognize Fe(CN)63- ions in water, with a detection limit of 2.5 × 10-8 M.

Stimuli-Responsive, Dynamic Supramolecular Organic Frameworks

Supramolecular organic frameworks (SOFs) are a class of three-dimensional, potentially porous materials obtained by the self-assembly of organic building blocks held together by weak interactions such as hydrogen bonds, halogen bonds, π⋅⋅⋅π stacking and dispersion forces. SOFs are being extensively studied for their potential applications in gas storage and separation, catalysis, guest encapsulation and sensing. The supramolecular forces that guide their self-assembly endow them with an attractive combination of crystallinity and flexibility, providing intelligent dynamic materials that can respond to external stimuli in a reversible way. The present review article will focus on SOFs showing dynamic behaviour when exposed to different stimuli, highlighting fundamental aspects such as the combination of tectons and supramolecular interactions involved in the framework formation, structure-property relationship and their potential applications.

Metal-organic rotaxane frameworks constructed from a cucurbit[8]uril-based ternary complex for the selective detection of antibiotics

Herein we report two 2D layered metal-organic rotaxane frameworks (MORFs), WUST-1 and WUST-2, constituted by a ternary host-guest complex based on cucurbit[8]uril (CB[8]) and an (E)-1-methyl-4-[4-(pyridin-4-yl)styryl] pyridinium (G1) ligand, and different metal ions and auxiliary linkers. Both MORFs are stable in water and highly fluorescence emissive, and can selectively sense nitrofurazone with low detection limits.

Highly Fluorescent Supramolecular Nanoring Composed of Bent-Shaped Cyanostilbene Derivatives and Cucurbit[8]urils

Supramolecular organic frameworks (SOFs) made of organic guest molecule and cucurbit[8]uril (CB[8]) in aqueous solution have great potential for diverse applications. Herein, we designed highly fluorescent zero-dimensional (0D) nano-ring SOF with CB[8] as a host and novel bent-shaped cyanostilbene guest. This host-guest complex successfully formed macrocyclic hexamer and showed significantly enhanced fluorescence (Φ_F =68 %) compared to non-assembled monomer (Φ_F =2 %). Unlike other SOFs, this 0D SOF could be dispersed uniformly without bundling phenomenon in water.

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.

Enhancing the therapeutic efficacy of nanoparticles for cancer treatment using versatile targeted strategies

Poor targeting of therapeutics leading to severe adverse effects on normal tissues is considered one of the obstacles in cancer therapy. To help overcome this, nanoscale drug delivery systems have provided an alternative avenue for improving the therapeutic potential of various agents and bioactive molecules through the enhanced permeability and retention (EPR) effect. Nanosystems with cancer-targeted ligands can achieve effective delivery to the tumor cells utilizing cell surface-specific receptors, the tumor vasculature and antigens with high accuracy and affinity. Additionally, stimuli-responsive nanoplatforms have also been considered as a promising and effective targeting strategy against tumors, as these nanoplatforms maintain their stealth feature under normal conditions, but upon homing in on cancerous lesions or their microenvironment, are responsive and release their cargoes. In this review, we comprehensively summarize the field of active targeting drug delivery systems and a number of stimuli-responsive release studies in the context of emerging nanoplatform development, and also discuss how this knowledge can contribute to further improvements in clinical practice.

Bottom-up supramolecular assembly in two dimensions

The self-assembly of molecules in two dimensions (2D) is gathering attention from all disciplines across the chemical sciences. Attracted by the interesting properties of two-dimensional inorganic analogues, monomers of different chemical natures are being explored for the assembly of dynamic 2D systems. Although many important discoveries have been already achieved, great challenges are still to be addressed in this field. Hierarchical multicomponent assembly, directional non-covalent growth and internal structural control are a just a few of the examples that will be discussed in this perspective about the exciting present and the bright future of two-dimensional supramolecular assemblies.

The self-assembly of molecules in two dimensions (2D) is gathering attention from all disciplines across the chemical sciences. This perspective discusses the main strategies to direct the supramolecular self-assembly of organic monomers in 2D.

Evidenced cucurbit[n]uril-based host-guest interactions using single-molecule force spectroscopy

In this work, enhanced guest-pair interactions in the cavity of cucurbit[8]uril (CB[8]) are quantitatively determined using single-molecule force spectroscopy (SMFS). Significantly, the light-driven dynamic conformational change of guest pairs leads to a rupture force switching between the connected and broken CB[8]-mediated heteroternary complexation with viologen and bis(azobenzene) derivatives. SMFS is further utilized to detect methyl viologen based on the competitive host-guest interaction toward the guest in CB[8] or CB[7]. These findings highlight the extraordinary power of SMFS in supramolecular chemistry and will contribute to the fundamental understanding of the mechanochemical behavior of host-guest interactions.

Self-Assembly of a Bilayer 2D Supramolecular Organic Framework in Water

Accurate control of the layer number of orderly stacked 2D polymers has been an unsettled challenge in self-assembly. Herein we describe the fabrication of a bilayer 2D supramolecular organic framework from a monolayer 2D supramolecular organic framework in water by utilizing the cooperative coordination of a rod-like bipyridine ligands to zinc porphyrin subunits of the monolayer network. The monolayer supramolecular framework is prepared from the co-assembly of an octacationic zinc porphyrin monomer and cucurbit[8]uril (CB[8]) in water through CB[8]-encapsulation-promoted dimerization of 4-phenylpyridiunium subunits that the zinc porphyrin monomer bear. The bilayer 2D supramolecular organic framework exhibits structural regularity in both solution and the solid state, which is characterized by synchrotron small-angle X-ray scattering and high-resolution transmission electron microscopic techniques. Atomic force microscopic imaging confirms that the bilayer character of the 2D supramolecular organic framework can be realized selectively on the micrometer scale.

Supramolecular Two-Dimensional Systems and Their Biological Applications

Various biological systems rely on the supramolecular assembly of biomolecules through noncovalent bonds for performing sophisticated functions. In particular, cell membranes, which are 2D structures in biological systems, have various characteristics such as a large surface, flexibility, and molecule-recognition ability. Supramolecular 2D materials based on biological systems provide a novel perspective for the development of functional 2D materials. The physical and chemical properties of 2D structures, attributed to their large surface area, can enhance the sensitivity of the detection of target molecules, molecular loading, and bioconjugation efficiency, suggesting the potential utility of functional 2D materials as candidates for biological systems. Although several types of studies on supramolecular 2D materials have been reported, supramolecular biofunctional 2D materials have not been reviewed previously. In this regard, the current advances in 2D material development using molecular assembly are discussed with respect to the rational design of self-assembling aromatic amphiphiles, the formation of 2D structures, and the biological applications of functional 2D materials.

A Woven Supramolecular Metal-Organic Framework Comprising a Ruthenium Bis(terpyridine) Complex and Cucurbit[8]uril: Enhanced Catalytic Activity toward Alcohol Oxidation

The self-assembly of a diamondoid woven supramolecular metal-organic framework wSMOF-1 has been achieved from intertwined [Ru(tpy)₂ ]²⁺ (tpy=2,2',6',2''-terpyridine) complex M1 and cucurbit[8]uril (CB[8]) in water, where the intermolecular dimers formed by the appended aromatic arms of M1 are encapsulated in CB[8]. wSMOF-1 exhibits ordered pore periodicity in both water and the solid state, as confirmed by a combination of ¹ H NMR spectroscopy, UV-vis absorption, isothermal titration calorimetry, dynamic light scattering, small angle X-ray scattering and selected area electron diffraction experiments. The woven framework has a pore aperture of 2.1 nm, which allows for the free access of both secondary and primary alcohols and tert-butyl hydroperoxide (TBHP). Compared with the control molecule [Ru(tpy)₂ ]Cl₂ , the [Ru(tpy)₂ ]²⁺ unit of wSMOF-1 exhibits a remarkably higher heterogeneous catalysis activity for the oxidation of alcohols by TBHP in n-hexane. For the oxidation of 1-phenylethan-1-ol, the yield of acetophenone was increased from 10 % to 95 %.

Cucurbit[7]uril-Mediated 2D Single-Layer Hybrid Frameworks Assembled by Tetraphenylethene and Polyoxometalate toward Modulation of the α-Chymotrypsin Activity

Construction of large-scale single-layer two-dimensional (2D) frameworks in water is significant due to their utilities in various fields. Utilizing macrocycle-mediated supramolecular self-assembly represents a promising approach; however, challenges still remain in their practical preparation. Here, we exploited a two-step supramolecular strategy to build 2D organic-inorganic hybrid frameworks at a micrometer scale in water. Taking advantage of the high binding affinity to cucurbit[7]uril (CB[7]), mono-quaternary ammonium tetraphenylethene (MQATPE) derivatives were first included with CB[7] to form a 1:1 complex (MQATPE@CB[7]). Then, just mixing the complex with anionic polyoxometalate Na₉[EuW₁₀O₃₆]·32H₂O (denoted as Eu-POM) in a 3:1 molar ratio leads to the formation of single-layer 2D films with tens of micrometers via electrostatic and π-π stacking interactions. The most unique feature of this strategy is that the steric effect imposed by CB[7] would not only lead the modules to adopt a periodic hexagonal assembly but also forbid stacking between layers through comparison with the merely multilayered 2D nanosheets self-assembled by MQATPE/Eu-POM. Interestingly, the charge interactions between MQATPE and Eu-POM would lead to the aggregation-induced emission (AIE) fluorescence of MQATPE, and white light emission could be obtained through the simple regulation of the contents of Eu-POM and MQATPE. Furthermore, due to the high surface areas and more accessible active sites, the single-layer films can act as an effective enzyme inhibitor to modulate the activity of α-chymotrypsin (ChT). These findings suggest a simple but universal approach for single-layer hybrid materials, which may hold promise for practical applications in photophysical and biomedical fields.

Emission enhancement of cationic tetraphenylethylene derivatives by encapsulation in a cucurbit[10]uril host in water

Encapsulation of cationic tetraphenylethylene guests in a cucurbit[10]uril host in water results in strong emission enhancement of these guests since the host–guest interaction caused restriction of intramolecular rotation.