Fluorescent dyes and their supramolecular host/guest complexes with macrocycles in aqueous solution

Self Assembled Cages with Mechanically Interlocked Cucurbiturils

We report preparation of (bis)aniline ligand 4 which contains a central viologen binding domain and its subcomponent self-assembly with aldehyde 5 and Fe(OTf)₂ in CH₃CN to yield tetrahedral assembly 6. Complexation of ligand 4 with CB[7] in the form of CB[7]•4•2PF₆ allows the preparation of assembly 7 which contains an average of 1.95 (range 1-3) mechanically interlocked CB[7] units. Assemblies 6 and 7 are hydrolytically unstable in water due to their imine linkages. Redesign of our system with water stable 2,2'-bipyridine end groups was realized in the form of ligands 11 and 16 which also contain a central viologen binding domain. Self-assembly of 11 with Fe(NTf₂)₂ gave tetrahedral MOP 12 as evidenced by ¹H NMR, DOSY, and mass spectrometric analysis. In contrast, isomeric ligand 16 underwent self-assembly with Fe(OTf)₂ to give cubic assembly 17. Precomplexation of ligands 11 and 16 with CB[7] gave the acetonitrile soluble CB[7]•11•2PF₆ and CB[7]•16•2PF₆ complexes. Self-assembly of CB[7]•11•2PF₆ with Fe(OTf)₂ gave tetrahedron 13 which contains on average 1.8 mechanically interlocked CB[7] units as determined by ¹H NMR, DOSY, and ESI-MS analysis. Self-assembly of CB[7]•16•2PF₆ with Fe(OTf)₂ gave cube 13 which contains 6.59 mechanically interlocked CB[7] units as determined by ¹H NMR and DOSY measurements.

Supramolecular Bioimaging through Signal Amplification by Combining Indicator Displacement Assay with Förster Resonance Energy Transfer

Fluorescent chemosensors are powerful imaging tools in the fields of life sciences and engineering. Based on the principle of supramolecular chemistry, indicator displacement assay (IDA) provides an alternative approach for constructing and optimizing chemosensors, which has the advantages of simplicity, tunability, and modularity. However, the application of IDA in bioimaging continues to face a series of challenges, including interfering signals, background noise, and inconsistent spatial location. Accordingly, we herein report a supramolecular bioimaging strategy of Förster resonance energy transfer (FRET)-assisted IDA by employing macrocyclic amphiphiles as the operating platform. By merging FRET with IDA, the limitations of IDA in bioimaging were addressed. As a proof of concept, the study achieved mitochondria-targeted imaging of adenosine triphosphate in live cells with signal amplification. This study opens a non-covalent avenue for bioimaging with advancements in tunability, generality, and simplicity, apart from the covalent approach.

Photophysical and NMR studies of encapsulation of 2-cyano-6-hydroxy benzothiazole in p-sulfonatocalix[6]arene and its biological applications

This work deals with the study of the interaction between 2-cyano-6-hydroxy benzothiazole (CHBT) and p-sulfonatocalix[6]arene (SCX6) at different pH values in aqueous medium by UV-visible absorption spectroscopy and steady-state fluorescence spectroscopy. The results demonstrate the strong influence of SCX6 on the fluorescence properties of CHBT. The steady-state emission of CHBT shows strong sensitivity to its environment. The mode of inclusion complexation of CHBT and SCX6 has also been investigated using HR-MS, FT-IR, NMR, 2D NMR, and FESEM analysis. With the increase in SCX6 concentration, absorbance decreased with an isosbestic point at 305 nm. The binding constant is calculated by a spectrofluorimetric method and stoichiometry by Job's method. The formation of an inclusion complex has been confirmed by 2D NMR NOESY, COSY, ROESY, HMBC, and HSQC spectroscopic methods. The complex is seen to be stabilized by electrostatic interactions between CHBT and the nanocavity of SCX6. Studies with cellular systems support that the CHBT-SCX6 complex is more effective in killing cancerous cells and hence, SCX6 may prove to be an effective carrier for drug molecules like CHBT.

Indicator displacement assays: from concept to recent developments

Overcoming the synthetic burden related to covalently connected receptors with appropriate indicators for sensing various analytes via an indicator spacer receptor (ISR) approach, the indicator displacement assay (IDA) seems to be a very sophisticated and versatile supramolecular sensing paradigm, and it has taken the phenomenon of molecular recognition to the next level in the realm of host-guest chemistry. Due to the unavailability of a comprehensive report on what has been done in the last decade in relation to IDAs, we decided to set down this account illustrating diverse indicator displacement assays (IDAs) in detail from the concept stage to recent developments relating to the detection of cationic, anionic, and neutral analytes. The authors conclude this account with future perspectives and highlight the limitations and challenges relating to IDAs which need to be overcome in order to realize the full potential of this popular sensing phenomenon. While we were finalizing our account for publication, a tutorial review by the research groups of Anslyn, Sessler, and Sun was published, which focuses mainly on diverse aspects of the chemistry related to IDAs. As can be seen, our review, besides discussing various basic IDA concepts, has a vast collection of information published in the past decade and hence, hopefully, will be very informative for the supramolecular community. We believe that this work will offer new insights for the construction of novel sensors operating through the IDA approach.

Stimuli Responsive Confinement of a Molecular Rotor Based BODIPY Dye inside a Cucurbit[7]uril Nanocavity

Present study reports the interaction of a molecular rotor based BODIPY dye, 8-anilino-BODIPY (ABP), with a versatile macrocyclic molecule, cucurbit[7]uril (CB7), investigated through various techniques such as ground-state absorption, steady-state fluorescence, time-resolve emission, proton NMR, and quantum chemical studies. Although BODIPY dyes have widespread applications due to their intriguing photochemical properties, studies on their noncovalent interactions with different macrocyclic hosts, especially regarding their supramolecularly induced modulations in photophysical properties are very limited. The investigated BODIPY dye, especially its protonated ABPH⁺ form (pH ∼ 1), shows a large fluorescence enhancement on its interaction with the CB7 host, due to large reduction in the structural flexibility for the bound dye, causing a suppression in its nonradiative de-excitation process in the excited state. Unlike ABPH⁺, the neutral ABP form (pH ∼ 7) shows considerably weaker interaction with CB7. For ABPH⁺-CB7 system, observed photophysical results indicate formation of both 1:1 and 1:2 dye-to-host complexes. Plausible geometries of these complexes are obtained from quantum chemical studies which are substantiated nicely from ¹H NMR results. The response of the ABPH⁺-CB7 system toward changing temperature of the solution have also been investigated elaborately to understand the potential of the system in different stimuli-responsive sensor applications.

Cucurbituril-Encapsulating Metal-Organic Framework via Mechanochemistry: Adsorbents with Enhanced Performance

The first examples of monolithic crystalline host-guest hybrid materials are described. The reaction of 1,3,5-benzenetricarboxylic acid (H3 BTC) and Fe(NO3 )3 ⋅9 H2 O in the presence of decamethylcucurbit[5]uril ammonium chloride (MC5⋅2 NH4 Cl⋅4 H2 O) directly affords MC5@MIL-100(Fe) hybrid monoliths featuring hierarchical micro-, meso- and macropores. Particularly, this "bottle-around-ship" synthesis and one-pot shaping are facilitated by a newly discovered Fe-MC5 flowing gel formed by mechanochemistry. The designed MC5@MIL-100(Fe) hybrid material with MC5 as active domains shows enhanced CH4 and lead(II) uptake performance, and selective capture of lead(II) cations at low concentrations. This shows that host-guest hybrid materials can exhibit synergic properties that out-perform materials based on individual components.

Cu(I)-Catalyzed Click Chemistry in Glycoscience and Their Diverse Applications

Copper(I)-catalyzed 1,3-dipolar cycloaddition between organic azides and terminal alkynes, commonly known as CuAAC or click chemistry, has been identified as one of the most successful, versatile, reliable, and modular strategies for the rapid and regioselective construction of 1,4-disubstituted 1,2,3-triazoles as diversely functionalized molecules. Carbohydrates, an integral part of living cells, have several fascinating features, including their structural diversity, biocompatibility, bioavailability, hydrophilicity, and superior ADME properties with minimal toxicity, which support increased demand to explore them as versatile scaffolds for easy access to diverse glycohybrids and well-defined glycoconjugates for complete chemical, biochemical, and pharmacological investigations. This review highlights the successful development of CuAAC or click chemistry in emerging areas of glycoscience, including the synthesis of triazole appended carbohydrate-containing molecular architectures (mainly glycohybrids, glycoconjugates, glycopolymers, glycopeptides, glycoproteins, glycolipids, glycoclusters, and glycodendrimers through regioselective triazole forming modular and bio-orthogonal coupling protocols). It discusses the widespread applications of these glycoproducts as enzyme inhibitors in drug discovery and development, sensing, gelation, chelation, glycosylation, and catalysis. This review also covers the impact of click chemistry and provides future perspectives on its role in various emerging disciplines of science and technology.

A Colorimetric Method for Quantifying Cis and Trans Alkenes Using an Indicator Displacement Assay

A colorimetric indicator displacement assay (IDA) amenable to high-throughput experimentation was developed to determine the percentage of cis and trans alkenes. Using 96-well plates two steps are performed: a reaction plate for dihydroxylation of the alkenes followed by an IDA screening plate consisting of an indicator and a boronic acid. The dihydroxylation generates either erythro or threo vicinal diols from cis or trans alkenes, depending upon their syn- or anti-addition mechanisms. Threo diols preferentially associate with the boronic acid due to the creation of more stable boronate esters, thus displacing the indicator to a greater extent. The generality of the protocol was demonstrated using seven sets of cis and trans alkenes. Blind mixtures of cis and trans alkenes were made, resulting in an average error of ±2 % in the percentage of cis or trans alkenes, and implementing E₂ and Wittig reactions gave errors of ±3 %. Furthermore, we developed variants of the IDA for which the color may be tuned to optimize the response for the human eye.

A Novel Fluorescent Probe for Hydrogen Peroxide and Its Application in Bio-Imaging

Hydrogen peroxide (H2O2) plays an important role in the human body and monitoring its level is meaningful due to the relationship between its level and diseases. A fluorescent sensor (CMB) based on coumarin was designed and its ability for detecting hydrogen peroxide by fluorescence signals was also studied. The CMB showed an approximate 25-fold fluorescence enhancement after adding H2O2 due to the interaction between the CMB and H2O2 and had the potential for detecting physiological H2O2. It also showed good biocompatibility and permeability, allowing it to penetrate cell membranes and zebrafish tissues, thus it can perform fluorescence imaging of H2O2 in living cells and zebrafish. This probe is a promising tool for monitoring the level of H2O2 in related physiological and pathological research.

Synthesis and Guest-Binding Properties of pH/Reduction Dual-Responsive Cyclophane Dimer

A water-soluble cyclophane dimer having two disulfide groups as a reduction-responsive cleavable bond as well as several acidic and basic functional groups as a pH-responsive ionizable group 1 was successfully synthesized. It was found that 1 showed pH-dependent guest-binding behavior. That is, 1 strongly bound an anionic guest, 6-p-toluidinonaphthalene-2-sulfonate (TNS) with binding constant (K/M⁻¹) for 1:1 host-guest complexes of 9.6 × 10⁴ M⁻¹ at pH 3.8, which was larger than those at pH 7.4 and 10.7 (6.0 × 10⁴ and 2.4 × 10⁴ M⁻¹, respectively), indicating a favorable electrostatic interaction between anionic guest and net cationic 1. What is more, release of the entrapped guest molecules by 1 was easily controlled by pH stimulus. Large favorable enthalpies (ΔH) for formation of host-guest complexes were obtained under the pH conditions employed, suggesting that electrostatic interaction between anionic TNS and 1 was the most important driving force for host-guest complexation. Such contributions of ΔH for formation of host-guest complexes decreased along with increased pH values from acidic to basic solutions. Upon addition of dithiothreitol (DTT) as a reducing reagent to an aqueous PBS buffer (pH 7.4) containing 1 and TNS, the fluorescence intensity originating from the bound guest molecules decreased gradually. A treatment of 1 with DTT gave 2, having less guest-binding affinity by the cleavage of disulfide bonds of 1. Consequently, almost all entrapped guest molecules by 1 were released from the host. Moreover, such reduction-responsive cleavage of 1 and release of bound guest molecules was performed more rapidly in aqueous buffer at pH 10.7.

From photosensitizers to light harvesters adapting the molecular structure in all-BODIPY assemblies

Herein we detail a protocol to design dyads and triads based solely on BODIPY dyes as halogen-free singlet oxygen photosensitizers or energy transfer molecular cassettes. The conducted photonic characterization reveals the key role of the BODIPY-BODIPY linkage to finely modulate the balance between the triplet state population and fluorescence decay.

Addressing the Exigent Role of a Coumarin Fluorophore toward Finding the Suitable Microenvironment of Biomimicking and Biomolecular Systems: Steering to Project the Drug Designing and Drug Delivery Study

The photophysics of 4-azidocoumarin (4-AC), a novel fluorescent coumarin derivative, is well established by the investigation of the alteration of the microheterogeneous environment comprising two types of systems: supramolecular systems, cyclodextrins (CDs), and biomolecular systems, serum albumins (SAs). The enhanced emission of the ligand with the organized assemblies like α-CD, β-CD, and γ-CD by steady-state and time-resolved fluorescence and fluorescence anisotropy at 298 K is compared with those of bovine serum albumin (BSA) and human serum albumin (HSA). The remarkable enhancement of the emission of ligand 4-AC along with the blue shift of the emission for both the systems are visualized as the incorporation of 4-AC into the hydrophobic core of the CDs and proteins mainly due to reduction of nonradiative decay process in the hydrophobic interior of CDs and SAs. The binding constants at 298 K and the single binding site are estimated using enhanced emission and anisotropy of the bound ligand in both the systems. The marked enhancement of the fluorescence anisotropy indicates that the ligand molecule experiences a motionally constrained environment within the CDs and SAs. Rotational correlation time (θ_c) of the bound ligand 4-AC is calculated in both the categories of the confined environment using time-resolved anisotropy at 298 K. Molecular docking studies for both the variety of complexes of the ligand throw light to assess the location of the ligand and the microenvironment around the ligand in the ligand-CD and ligand-protein complexes. Solvent variation study of the probe 4-AC molecule in different polar protic and aprotic solvents clearly demonstrates the polarity and hydrogen-bonding ability of the solvents, which supports the alteration of the microenvironments around 4-AC due to binding with the biomimicking as well as biomolecular systems. Dynamic light scattering is employed to determine the hydrodynamic diameter of free BSA/HSA and complexes of BSA/HSA with the ligand 4-AC.

Host-guest binding in water, salty water, and biofluids: general lessons for synthetic, bio-targeted molecular recognition

Synthetic molecular recognition systems are increasingly being used to solve applied problems in the life sciences, and bio-targeted host-guest chemistry has rapidly arisen as a major field of fundamental research. This tutorial review presents a set of fundamental lessons on how host-guest molecular recognition can be programmed in water. The review uses informative examples of aqueous host-guest chemistry organized around generalizable themes and lessons, building towards lessons focused on molecular recognition in salty solutions and biological fluids. It includes selected examples of macrocyclic host systems that work well, as well as common pitfalls and how to avoid them. The review closes with a survey of the most important and inspirational recent advances, which involve host-guest chemistry in living cells and organisms.

Supramolecular Control of Reactivity toward Hydrolysis of 7-Diethylaminocoumarin Schiff Bases by Cucurbit[7]uril Encapsulation

A series of aromatic Schiff bases, featuring 7-diethylamino-coumarin and with five different substituents at an adjacent phenyl ring, were synthesized and characterized. With the aim of assessing the stability of these dyes in acidic medium, their hydrolysis reactions were kinetically studied in the absence and presence of the macrocycle cucurbit[7]uril (CB[7]). Our results are consistent with a model containing three different forms of substrates (un-, mono-, and diprotonated) and three parallel reaction pathways. The pK a values and the rate constants were estimated and discussed in terms of the presence of a hydroxyl group at the ortho position and electron-releasing groups on the phenyl ring of the dyes. The kinetic study in the presence of CB[7] led to two different behaviors. Promotion of the reaction by CB[7] was observed for the hydrolysis of the Schiff bases containing only one coordination site toward the macrocycle. Conversely, an inhibitor effect was observed for the hydrolysis of a Schiff base with two coordination sites toward CB[7]. The latter effect could be explained with a model as a function of a prototropic tautomeric equilibrium and the formation of a 2:1 host/guest complex, which prevents the attack of water. Therefore, the kinetic results demonstrated a supramolecular control of the macrocycle toward the reactivity and stability of 7-diethylaminocoumarin Schiff bases in acidic medium.

Development of Water Solubility of 2-Phenylsulfanylhydroquinone Dimer Dye

With the aim of developing a new fluorescence dye with enhanced photophysical properties, this study describes the modification of the 2-phenylsulfanylhydroquinone dimer to realize a new bioimaging molecule. The characteristics of the dimer were advanced by introducing tetraethylene glycol side chains to provide sufficient water solubility and a tether consisting of an N-hydroxysuccinimide-terminated C6-carbon chain to attach bioactive molecules. Two derivatives containing two or three tetraethylene glycol side chains were designed and prepared, and the latter showed sufficient water solubility for biochemical applications. Both compounds exhibited similar photophysical properties and blue fluorescence under UV light irradiation. The dye containing three tetraethylene glycol units reacted with bovine serum albumin in water to give fluorescent derivatives.

Bright and Robust Phosphorescence Achieved by Non-Covalent Clipping

Phosphorescent materials with bright emission in versatile media are important for their practical applications, which require to lower the susceptibility of triplet excitons to surroundings. Herein a non-covalent clipping strategy has been developed to attain this objective, by designing a tweezer receptor to encapsulate Pt^II -based triplet emitters through two-fold π-stacking interactions. The Pt^II emitters display robust phosphorescence by virtue of synergistic rigidifying and shielding effects, which are hardly influenced by emitter concentration, oxygen content, and solvent polarity changes. The phosphorescent colors are elaborately modulated by varying ligand substitutes on Pt^II emitters. Circularly polarized phosphorescence is further amplified for chiral Pt^II emitters, by taking advantage of dual phosphorescence and chirality enhancement upon non-covalent tweezer complexation. Overall, the clipping approach paves the way for the development of high-performance phosphorescent materials with bright emission, environmental robustness, and facile color tunability.

Supramolecular and suprabiomolecular photochemistry: a perspective overview

In this perspective review article, we have attempted to bring out the important current trends of research in the areas of supramolecular and suprabiomolecular photochemistry. Since the spans of the subject areas are very vast, it is impossible to cover all the aspects within the limited space of this review article. Nevertheless, efforts have been made to assimilate the basic understanding of how supramolecular interactions can significantly change the photophysical and other related physiochemical properties of chromophoric dyes and drugs, which have enormous academic and practical implications. We have discussed with reference to relevant chemical systems where supramolecularly assisted modulations in the properties of chromophoric dyes and drugs can be used or have already been used in different areas like sensing, dye/drug stabilization, drug delivery, functional materials, and aqueous dye laser systems. In supramolecular assemblies, along with their conventional photophysical properties, the acid-base properties of prototropic dyes, as well as the excited state prototautomerization and related proton transfer behavior of proton donor/acceptor dye molecules, are also largely modulated due to supramolecular interactions, which are often reflected very explicitly through changes in their absorption and fluorescence characteristics, providing us many useful insights into these chemical systems and bringing out intriguing applications of such changes in different applied areas. Another interesting research area in supramolecular photochemistry is the excitation energy transfer from the donor to acceptor moieties in self-assembled systems which have immense importance in light harvesting applications, mimicking natural photosynthetic systems. In this review article, we have discussed varieties of these aspects, highlighting their academic and applied implications. We have tried to emphasize the progress made so far and thus to bring out future research perspectives in the subject areas concerned, which are anticipated to find many useful applications in areas like sensors, catalysis, electronic devices, pharmaceuticals, drug formulations, nanomedicine, light harvesting, and smart materials.

Ultrasensitive supersandwich-type electrochemical sensor for SARS-CoV-2 from the infected COVID-19 patients using a smartphone

The recent pandemic outbreak of COVID-19 caused by a novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), poses a threat to public health globally. Thus, developing a rapid, accurate, and easy-to-implement diagnostic system for SARS-CoV-2 is crucial for controlling infection sources and monitoring illness progression. Here, we reported an ultrasensitive electrochemical detection technology using calixarene functionalized graphene oxide for targeting RNA of SARS-CoV-2. Based on a supersandwich-type recognition strategy, the technology was confirmed to practicably detect the RNA of SARS-CoV-2 without nucleic acid amplification and reverse-transcription by using a portable electrochemical smartphone. The biosensor showed high specificity and selectivity during in silico analysis and actual testing. A total of 88 RNA extracts from 25 SARS-CoV-2-confirmed patients and eight recovery patients were detected using the biosensor. The detectable ratios (85.5 % and 46.2 %) were higher than those obtained using RT-qPCR (56.5 % and 7.7 %). The limit of detection (LOD) of the clinical specimen was 200 copies/mL, which is the lowest LOD among the published RNA measurement of SARS-CoV-2 to date. Additionally, only two copies (10 μL) of SARS-CoV-2 were required for per assay. Therefore, we developed an ultrasensitive, accurate, and convenient assay for SARS-CoV-2 detection, providing a potential method for point-of-care testing.

Cyclodextrin Polymers and Cyclodextrin-Containing Polysaccharides for Water Remediation

Chemical pollution of water has raised great concerns among citizens, lawmakers, and nearly all manufacturing industries. As the legislation addressing liquid effluents becomes more stringent, water companies are increasingly scrutinized for their environmental performance. In this context, emergent contaminants represent a major challenge, and the remediation of water bodies and wastewater demands alternative sorbent materials. One of the most promising adsorbing materials for micropolluted water environments involves cyclodextrin (CD) polymers and cyclodextrin-containing polysaccharides. Although cyclodextrins are water-soluble and, thus, unusable as adsorbents in aqueous media, they can be feasibly polymerized by using different crosslinkers such as epichlorohydrin, polycarboxylic acids, and glutaraldehyde. Likewise, with those coupling agents or after substituting hydroxyl groups with more reactive moieties, cyclodextrin units can be covalently attached to a pre-existing polysaccharide. In this direction, the functionalization of chitosan, cellulose, carboxymethyl cellulose, and other carbohydrate polymers with CDs is vastly found in the literature. For the system containing CDs to be used for remediation purposes, there are benefits from a synergy that arises from (i) the ability of CD units to interact selectively with a broad spectrum of molecules, forming inclusion complexes and higher-order supramolecular assemblies, (ii) the functional groups of the crosslinker comonomers, (iii) the three-dimensional structure of the crosslinked network, and/or (iv) the intrinsic characteristics of the polysaccharide backbone. In view of the most recent contributions regarding CD-based copolymers and CD-containing polysaccharides, this review discusses their performance as adsorbents in micropolluted water environments, as well as their interaction patterns, addressing the influence of their structural and physicochemical properties and their functionalization.

Multifunctional biohybrid magnetite microrobots for imaging-guided therapy

Magnetic microrobots and nanorobots can be remotely controlled to propel in complex biological fluids with high precision by using magnetic fields. Their potential for controlled navigation in hard-to-reach cavities of the human body makes them promising miniaturized robotic tools to diagnose and treat diseases in a minimally invasive manner. However, critical issues, such as motion tracking, biocompatibility, biodegradation, and diagnostic/therapeutic effects, need to be resolved to allow preclinical in vivo development and clinical trials. We report biohybrid magnetic robots endowed with multifunctional capabilities by integrating desired structural and functional attributes from a biological matrix and an engineered coating. Helical microswimmers were fabricated from Spirulina microalgae via a facile dip-coating process in magnetite (Fe₃O₄) suspensions, superparamagnetic, and equipped with robust navigation capability in various biofluids. The innate properties of the microalgae allowed in vivo fluorescence imaging and remote diagnostic sensing without the need for any surface modification. Furthermore, in vivo magnetic resonance imaging tracked a swarm of microswimmers inside rodent stomachs, a deep organ where fluorescence-based imaging ceased to work because of its penetration limitation. Meanwhile, the microswimmers were able to degrade and exhibited selective cytotoxicity to cancer cell lines, subject to the thickness of the Fe₃O₄ coating, which could be tailored via the dip-coating process. The biohybrid microrobots reported herein represent a microrobotic platform that could be further developed for in vivo imaging-guided therapy and a proof of concept for the engineering of multifunctional microrobotic and nanorobotic devices.

Supramolecular hydrogels prepared from fluorescent alkyl pyridinium acrylamide monomers and CB[8]

Facile synthetic methodology unlocks alkyl pyridinium acrylamide monomers for use in the construction of cucurbit[8]uril mediated dynamic, fluorescent hydrogels.

Fluorescence visualization of cucurbit[8]uril-triggered dynamic host–guest assemblies

Dynamic assemblies of π-conjugated bispyridinium guests with cucurbit[8]uril in aqueous solution could be distinguished by real-time naked-eye observation of the resulting quantitative fluorescence emissions.

Cucurbituril-assisted formation of tunable carbon dots from single organic precursors in water

A facile method by utilizing the host–guest interaction of Q[n]s for the catalytic fabrication of CDs with high emitting qualities and a tunable particle size from a single organic precursor in water with high output has been demonstrated.

Additive-free N-methylation of amines with methanol over supported iridium catalyst

Clean N-methylation of amines with methanol was achieved, providing a green approach to the selective synthesis of mono- or di-methylated amines.

Fluorophore-Appendant 5,5'-Bicalixarene Scaffolds for Host-Guest Sensing of Nitric Oxide

Conjugated 5,5′-Bicalixarene scaffolds having fluorophores at the chain termini have been prepared and tested in the supramolecular detection of nitric oxide. Scaffolds bearing electron-rich fluorophores demonstrated a stronger turn-off response to the presence of NO than the fluorophore-free analogue in both organic and aqueous media, while no fluorescence quenching happened when the electron-deficient fluorophores were employed. Unprecedented ratiometric supramolecular sensing was observed when fluorophores of the opposite electronic demands were placed at the scaffold’s termini.

Self-Assembly of Pseudo[1]rotaxanes by Palladium(II)/Platinum(II)-Directed Integrative Social Self-Sorting: Is the Metal Required?

New results are presented on the multicomponent supramolecular synthesis of pseudo[1]rotaxanes, achieved by designing pairs of structurally matching N-monoalkyl-4,4'-bipyridinium/2,7-diazapyrenium-based ligands having complementary π-donor/acceptor features, and intended to self-assemble into the targeted supramolecules by following integrative self-sorting processes. In all the studied cases, it was found that the envisioned species, characterized by NMR spectroscopy and MS spectrometry, arise as the main products of the self-assembly in aqueous media by using palladium(II)/platinum(II) metal centers as the guiding force. Crucially, we have also found that by improving the π-donor/acceptor properties of the matching pairs of ligands (L₄ and L₅ ), the integrative self-sorting processes prevail even in the absence of metallic ions to afford the heterodimeric species with an association constant being 756±43 M^-1 .

Fluorescence Enhancement by Calixarene Supramolecular Aggregate

We herein constructed supramolecular assemblies from guanidinocalixarenes and sulfonatocalixarenes by exploiting multiple salt bridge interactions. They encapsulate six different kinds of fluorescent dyes (both cationic and anionic), leading to a fluorescence enhancement that could not be achieved by either single calixarene. As such, this study advances the research on high-performance fluorophores.