Specific Host-guest Interactions Research Articles

2D MOF-enhanced SPR detector based on tunable supramolecular probes for direct and sensitive detection of DOX in serum.

Therapeutic drug monitoring of doxorubicin (DOX) is important to studypharmacokinetics in patients undergoing chemotherapy for reduction ofside effects and improve patient survival by rationally controlling the dose of DOX. A fast and ultra-sensitive surface plasmon resonance (SPR) detector without sample pre-handling was developed for DOX monitoring. First, the two-dimensional metal-organic framework was modified on the Au film to enhance SPR, and then, the supramolecular probes with tunable cavity structure were self-assembled at the sensing interface for direct detection of DOX through specific host-guest interactions with a low detection limit of 60.24pM. The precise monitoring of DOX in serum proved the possibility of clinical application with recoveries in the range 102.86-109.47%. The mechanisms of host-guest interactions between supramolecular and small-molecule drugs were explored in depth through first-principles calculations combined with SPR experiments. The study paves the way for designing facile and sensitive detectors and provides theoretical support and a new methodology for the specific detection of small molecules through calixarene cavity modulation.

Protomer of Imipramine Captured in Cucurbit[7]uril.

Small molecules possessing multiple proton-accessible sites are important not only to many biological systems but also to host-guest chemistry; their protonation states are causal to boosting or hindering specific host-guest interactions. However, determining the protonation site is not trivial. Herein, we conduct electrospray ionization ion mobility spectrometry-mass spectrometry to imipramine, a known molecule with two protonation sites, based on the introduction of cucurbit[7]uril as a host molecule. For protonated imipramine, the proposed strategy allows clear distinction of the two protomers as host-guest complex ions and can be leveraged to capture the energetically less preferable protomer of the protonated imipramine.

Analysis of a Cu-Doped Metal-Organic Framework, MFM-520(Zn1-x Cux ), for NO2 Adsorption.

MFM-520(Zn) confines dimers of NO2 with a high adsorption of 4.52mmol g-1 at 1bar at 298 K. The synthesis and the incommensurate structure of Cu-doped MFM-520(Zn) are reported. The introduction of paramagnetic Cu2+ sites allows investigation of the electronic and geometric structure of metal site by in situ electron paramagnetic resonance (EPR) spectroscopy upon adsorption of NO2 . By combining continuous wave and electron-nuclear double resonance spectroscopy, an unusual reverse Berry distorted coordination geometry of the Cu2+ centers is observed. Interestingly, Cu-doped MFM-520(Zn0.95 Cu0.05 ) shows enhanced adsorption of NO2 of 5.02mmol g-1 at 1bar at 298 K. Whereas MFM-520(Zn) confines adsorbed NO2 as N2 O4 , the presence of monomeric NO2 at low temperature suggests that doping with Cu2+ centers into the framework plays an important role in tuning the dimerization of NO2 molecules in the pore via the formation of specific host-guest interactions.

Crosslinked and Multi-Responsive Polymeric Vesicles as a Platform to Study Enzyme-Mediated Undocking Behavior: Toward Future Artificial Organelle Communication.

Various cellular functions are successfully mimicked, opening the door to the next generation of therapeutic approaches and systems biology. Herein, the first steps are taken toward the construction of artificial organelles for mimicking cell communication by docking and undocking of cargo in the membrane of swollen artificial organelles. Stimuli-responsive and crosslinked polymeric vesicles are used to allow docking processes at acidic pH at which ferrocene units in the swollen membrane state can undergo desired specific host-guest interaction using β-cyclodextrin as model cargo. The release of the cargo mediated by two different enzymes, glucose oxidase and α-amylase, is investigated, triggered by distinct enzymatic undocking mechanisms. Different release times for a useful transport are shown that can be adapted to different communication pathways. In addition, Försterresonanceenergytransfer(FRET) experiments further support the hypotheses of host-guest inclusion complexation formation and their time-dependent breakdown. This work paves a way to a platform based on polymeric vesicles for synthetic biology, cell functions mimicking, and the construction of multifunctional cargo delivery system.

Fluorescence Nanoparticle Sensor Array Combined with Multidimensional Data Processing for the Determination of Small Organics and the Identification of Baijiu

The discrimination and determination of small organics may be employed for baijiu identification. A single nanoparticle was designed as a fluorescence sensor to address this issue. Via specific host-guest interactions, small organics may significantly disrupt the energy transmission of nanoparticles, resulting in sharp changes in characteristic fluorescence peaks, thus allowing the discrimination of single substances or mixtures by principal component analysis (PCA), hierarchical clustering analysis (HCA), and linear discriminant analysis (LDA). The system was characterized by transmission electron microscopy with energy dispersive spectrometry and fluorescence spectroscopy. 15 small flavor organics in baijiu were successfully discriminated. Moreover, the linear relationship between the concentrations of tryptophan and ethyl butyrate with the corresponding responsiveness demonstrated the capabilities of the sensor. The reported device was successfully applied to distinguish 16 baijiu brands. This simple and rapid method has outstanding potential for the characterization of alcoholic beverages.

Self-Assembly of Cyclodextrin-Coated Nanoparticles:Fabrication of Functional Nanostructures for Sensing and Delivery.

In recent years, the bottom-up approach has emerged as a powerful tool in the fabrication of functional nanomaterials through the self-assembly of nanoscale building blocks. The cues embedded at the molecular level provide a handle to control and direct the assembly of nano-objects to construct higher-order structures. Molecular recognition among the building blocks can assist their precise positioning in a predetermined manner to yield nano- and microstructures that may be difficult to obtain otherwise. A well-orchestrated combination of top-down fabrication and directed self-assembly-based bottom-up approach enables the realization of functional nanomaterial-based devices. Among the various available molecular recognition-based "host-guest" combinations, cyclodextrin-mediated interactions possess an attractive attribute that the interaction is driven in aqueous environments, such as in biological systems. Over the past decade, cyclodextrin-based specific host-guest interactions have been exploited to design and construct structural and functional nanomaterials based on cyclodextrin-coated metal nanoparticles. The focus of this review is to highlight recent advances in the self-assembly of cyclodextrin-coated metal nanoparticles driven by the specific host-guest interaction.

LiBF4‐Induced Rearrangement and Desymmetrization of a Palladium‐Ligand Assembly

AbstractThirteen palladium‐ligand assemblies with different structures and topologies were investigated for the ability to bind lithium ions. In one case, the addition of LiBF4 resulted in a profound structural rearrangement, converting a dincluclear [Pd2L4]4+ complex into a low‐symmetry [Pd4L8]8+ assembly with two binding pockets for solvated LiBF4 ion pairs. The rearrangement could only be induced by Li+, indicating highly specific host–guest interactions. A structural analysis of the [Pd4L8]8+ receptor revealed a compact structure with multiple intramolecular interactions, reminiscent of what is seen for natural and synthetic foldamers.

LiBF4 -Induced Rearrangement and Desymmetrization of a Palladium-Ligand Assembly.

Thirteen palladium‐ligand assemblies with different structures and topologies were investigated for the ability to bind lithium ions. In one case, the addition of LiBF4 resulted in a profound structural rearrangement, converting a dincluclear [Pd2L4]4+ complex into a low‐symmetry [Pd4L8]8+ assembly with two binding pockets for solvated LiBF4 ion pairs. The rearrangement could only be induced by Li+, indicating highly specific host–guest interactions. A structural analysis of the [Pd4L8]8+ receptor revealed a compact structure with multiple intramolecular interactions, reminiscent of what is seen for natural and synthetic foldamers.

Smart Tetraphenylethene-Based Luminescent Metal-Organic Frameworks with Amide-Assisted Thermofluorochromics and Piezofluorochromics.

Luminescent metal–organic frameworks (MOFs) are appealing for the design of smart responsive materials, whereas aggregation‐induced emission (AIE) fluorophores with twisted molecular rotor structure provide exciting opportunities to construct MOFs with new topology and responsiveness. Herein, it is reported that elongating AIE rotor ligands can render the newly formed AIE MOF (ZnETTB) (ETTB = 4',4''',4''''',4'''''''‐(ethene‐1,1,2,2‐tetrayl)tetrakis(([1,1'‐biphenyl]‐3,5‐dicarboxylic acid))) with more elasticity, more control for intramolecular motion, and specific amide‐sensing capability. ZnETTB shows specific host–guest interaction with amide, where N,N‐diethylformamide (DEF), as an example, is anchored through C—H···O and C—H···π bonds with Zn cluster and ETTB8− ligand, respectively. DEF anchoring reduces both the distortion level and the intramolecular motions of ETTB8− ligand to lead a blueshifted and intensified emission for DEF ∈ ZnETTB. Moreover, amide anchoring also affords the DEF ∈ ZnETTB with the excellent thermofluorochromic behavior, and further increases the piezofluorochromic sensitivity at low‐pressure ranges on the basis of its elastic framework. This work is one of the rare examples of amide‐responsive smart materials, which shall shed new lights on design of smart MOFs with twisted AIE rotors for further sensing and detection applications.

Binary and Ternary Complexes of Cucurbit[8]uril with Tryptophan, Phenylalanine, and Tyrosine: A Computational Study.

Selective binding of amino acids, peptides, and proteins by synthetic molecules and elucidation of the geometry and dynamics of the resulting complexes and their strengths are active areas of contemporary research. In recent work, we analyzed via molecular dynamics (MD) simulations the complexes formed between cucurbit[7]uril (CB7) and three aromatic amino acids: tryptophan (W), phenylalanine (F), and tyrosine (Y). Herein, we continue this line of research by performing MD simulations lasting 100 ns to investigate the formation, stabilities, binding modes, dynamics, and specific host–guest noncovalent interactions contributing to the formation of the binary (1:1) and ternary (2:1) complexes in aqueous solution between W, F, and Y amino acids and cucurbit[8]uril (CB8). All complexes were found to be stable, with the binding in each complex dominated by one mode (except for the F–CB8 complex, which had two) characterized by encapsulation of the aromatic side chains of the amino acids within the cavity of CB8 and the exclusion of their ammonium and carboxylate groups. Using the molecular mechanics/Poisson–Boltzmann surface area method to estimate the individual contributions to the overall free energies of binding, results revealed that the key role is played by the amino acid side chains in stabilizing the complexes through their favorable van der Waals interactions with the CB8 cavity and the importance of favorable electrostatic interactions between the carbonyl portal of CB8 and the ammonium group of the amino acid. Visual analysis of structures of the ternary complexes indicated the presence of π–π stacking between the aromatic side chains of the included amino acids. The insights provided by this work may be of value for further efforts aiming to employ the recognition properties of CB8 toward amino acids in applications requiring more elaborate recognition of short peptides and proteins.

Ionic metal-organic frameworks (iMOFs): progress and prospects as ionic functional materials.

Metal-organic frameworks (MOFs) have been a research hotspot for the last two decades, witnessing an extraordinary upsurge across various domains in materials chemistry. Ionic MOFs (both anionic and cationic MOFs) have emerged as next-generation ionic functional materials and are an important subclass of MOFs owing to their ability to generate strong electrostatic interactions between their charged framework and guest molecules. Furthermore, the presence of extra-framework counter-ions in their confined nanospaces can serve as additional functionality in these materials, which endows them a significant advantage in specific host-guest interactions and ion-exchange-based applications. In the present review, we summarize the progress and future prospects of iMOFs both in terms of fundamental developments and potential applications. Furthermore, the design principles of ionic MOFs and their state-of-the-art ion exchange performances are discussed in detail and the future perspectives of these promising ionic materials are proposed.

Dynamic nanosurface reconfiguration by host-guest supramolecular interactions.

The dynamic functionalization of the nanoparticle surface with biocompatible coatings is a critical step towards the development of functional nano-sized systems. While covalent approaches have been broadly exploited in the stabilization of nanoparticle colloidal systems, these strategies hinder the dynamic nanosurface chemical reconfiguration. Supramolecular strategies based on specific host-guest interactions hold promise due to their intrinsic reversibility, self-healing capabilities and modularity. Host/guest couples have recently been implemented in nanoparticle platforms for the exchange and release of effector molecules. However, the direct exchange of biocompatible hydrophilic oligomers (e.g. peptides) for the modulation of the surface charge and chemical properties of nanoparticles still remains a challenge. Here, we show the intracellular reconfiguration of nanoparticles by a host/guest mechanism with biocompatible oligomeric competitors. The surface of gold nanoparticles was functionalized with cyclodextrin hosts and the guest exchange was studied with biocompatible mono and divalent adamantyl competitors. The systematic characterization of the size and surface potential of the host/guest nanoparticles allowed the optimization of the binding and the stabilization properties of these supramolecular systems. The in cellulo host/guest-mediated direct reconfiguration of the peptide layer at the surface of nanoparticles is achieved by controlling the valence of adamantane-equipped peptides. This work demonstrates that host/guest supramolecular systems can be exploited for the direct exchange of pendants at the surface of nanoparticles and the intracellular dynamic chemical reconfiguration of biocompatible colloidal systems.

Supramolecular repair of hydration lubrication surfaces

<h2>Summary</h2> Although advances in coating technologies have allowed us to match—or even exceed—the lubricity of Nature's low-friction surfaces, the performance of synthetic materials inevitably diminishes over time as the surfaces are worn and damaged by irreversible breakage of covalent bonds. Synthetic systems lack the bespoke repair mechanisms that replenish hydration lubrication surfaces in Nature. Here, we demonstrate dynamic repair of low-friction surfaces prepared through a surface-selective self-assembly strategy. Monolayers of lubricating polymers associate with functionalized surfaces through strong and specific host–guest interactions, leading to hydration lubrication surfaces with low coefficients of friction (0.024–0.028). Following friction-induced dissociation of the polymers, the polymer-to-surface interaction is restored by the reformation of host–guest complexes, thus repairing the monolayer, renewing the lubricity, and reducing the effects of wear. Such dynamically restored low-friction materials will be an essential tool in decreasing global energy use—a fifth of which is expended overcoming friction.

Cationic Effects on the Structural Dynamics of the Metal Ion-Crown Ether Complexes Investigated by Ultrafast Infrared Spectroscopy.

It is usually believed that the binding affinity and selectivity of an alkali metal ion with crown ether are defined by the size matching model. However, the underlying mechanism of the specific host-guest interactions and the structural dynamics of the metal ions confined in the cavity of the crown ethers in the solutions are still not clear. In this report, a series of alkali thiocyanate salts (XSCN; X = Li, Na, K, and Cs) complexed with 18-crown-6 (a typical crown ether) in the chloroform solutions were studied by the polarization-selective infrared pump-probe spectroscopy and the ultrafast two-dimensional infrared (2D IR) spectroscopy. The SCN- counteranions were employed as the local vibrational probe to reveal the specific host-guest interactions in the crown ether complexes. The rotational dynamics and spectral diffusion of SCN- vibration were both measured by ultrafast IR spectroscopy, and it was found that the metal cations hosted by the crown ethers can have a pronounced effect on the rotational dynamics of the counteranions. The reorientational time constants of the SCN- vibration in the complexation follow the order Li+ > Na+ > K+ ≃ Cs+. More importantly, the spectral diffusion dynamics of SCN-, which quantifies the decay of the correlation of the frequency fluctuations in the complexation, was also affected by the metal ions but showed a different order of cationic effect. A detailed analysis of the 2D IR data showed that the spectral diffusion of SCN- counteranion clearly decayed with two different time scales in the complex of 18-crown-6 with K+. The 3-4-fold slowdown in spectral diffusion indicated that the fluctuation of SCN- vibrational transition frequency was strongly affected by the K+ cation due to the geometric constraint imposed by the crown ether. The results should help the researchers to unravel the specific host-guest interactions and further reveal the origination of the binding selectivity of crown ether for metal cations in the condensed phases from the perspective of structural dynamics.

Evolution of Supramolecular Systems Towards Next-Generation Biosensors.

Supramolecular materials, which rely on dynamic non-covalent interactions, present a promising approach to advance the capabilities of currently available biosensors. The weak interactions between supramolecular monomers allow for adaptivity and responsiveness of supramolecular or self-assembling systems to external stimuli. In many cases, these characteristics improve the performance of recognition units, reporters, or signal transducers of biosensors. The facile methods for preparing supramolecular materials also allow for straightforward ways to combine them with other functional materials and create multicomponent sensors. To date, biosensors with supramolecular components are capable of not only detecting target analytes based on known ligand affinity or specific host-guest interactions, but can also be used for more complex structural detection such as chiral sensing. In this Review, we discuss the advancements in the area of biosensors, with a particular highlight on the designs of supramolecular materials employed in analytical applications over the years. We will first describe how different types of supramolecular components are currently used as recognition or reporter units for biosensors. The working mechanisms of detection and signal transduction by supramolecular systems will be presented, as well as the important hierarchical characteristics from the monomers to assemblies that contribute to selectivity and sensitivity. We will then examine how supramolecular materials are currently integrated in different types of biosensing platforms. Emerging trends and perspectives will be outlined, specifically for exploring new design and platforms that may bring supramolecular sensors a step closer towards practical use for multiplexed or differential sensing, higher throughput operations, real-time monitoring, reporting of biological function, as well as for environmental studies.

Flexible Lead-Free X-ray Detector from Metal-Organic Frameworks.

Semiconductive metal-organic frameworks (MOFs) obtained by specific host-guest interactions have attracted a large interest in the last two decades, promising development of next-generation electronic devices. Herein, we designed and presented flexible X-ray detectors using Ni-DABDT (DABDT = 2,5-diamino-1,4-benzenedithiol dihydrochloride) MOFs as the absorbing layer. The π-d coupling interactions of Ni-DABDT throughout the framework implement a conspicuous carrier transportation pathway. The detector that converts X-ray photons directly into carriers manifests an attractive achievement with high detection sensitivity of 98.6 μC Gyair-1 cm-2, with a low detection limit of 7.2 μGyair s-1 for the radiation robustness. This work provides insights for next-generation green and high-performance flexible sensor detectors by utilizing MOF materials with the benefits of a designable structure and tunable property, demonstrating a proof-of-concept in wearable X-ray detectors for radiation monitoring and imaging.

Facile fabrication of carbon-loaded covalent-organic framework composites with enhanced electrochemical performance for dopamine determination

In this work, a crystalline electroactive triphenylamine-based covalent-organic framework (TPA-COF) was composited with carbon black (CB) using a facile one-pot solvothermal method. It is shown that the loaded amount of CB significantly affects the electrochemical performance of the composites. On one hand, CB dispersed in the COF matrix can improve the conductivity of the composite. On the other hand, the π - π interactions between COF layers and carbon particles may affect the accumulation of COF layers, resulting in the increasement of the surface area and the exposure of active sites. These structural advantages promote the performance of the composite toward dopamine (DA) detection. When 30 wt% CB was loaded, the composite modified electrode demonstrates best activity with a wide linear range of 20 μ M–1000 μ M and a low detection limit of 0.17 μ M (S/N = 3). Moreover, due to its high selectivity, satisfying stability, and good repeatability, the constructed electrochemical sensor was successfully used to detect the DA concentration in real medical injection with satisfactory recovery results, that is in the range of 98.7–111.0%. Further studies show that the good performance of the constructed sensor is attributed to its good conductivity, high specific surface area and effective host guest interaction between DA molecules and COF framework. This work provides a simple method to utilize COFs for quantitative detection of DA, as well as a new way to extend the applications of COFs in sensing. A serial of composites composed of crystalline two-dimensional COF and carbon black was synthesized by using one pot method. Owing to its improved conductivity and highly porous structure, TPA-COF/CB 0.3 was developed as an electrochemical sensor for dopamine determination. • A series of porous carbon-loaded TPA-COF composites were facile prepared by one-pot solvothermal method. • The loaded carbon black effectively promotes the conductivity and the specific surface area of the composites. • TPA-COF/CB 0.3 @GCE reveals good electrochemical performance toward dopamine detection. • TPA-COF/CB 0.3 @GCE was successfully used to detect the dopamine concentration in real medical injection.

Supramolecular hydrogelation via host-guest anion recognition: Lamellar hydrogel materials for the release of cationic cargo

•Lamellar hydrogels are formed utilizing host-guest anion recognition in water•Selective hydrogelation in the presence of iodide or perchlorate was demonstrated•Macrocyclic anion receptor was used as a low molecular weight hydrogelator•Hydrogels released choline derivatives via cation metathesis Hydrogel materials that utilize host-guest chemistry for their formation have been extensively investigated for cationic and neutral guests and successfully employed in various fields of life sciences. Host-guest anion recognition has been elusive in this respect in spite of the high importance of anionic species in biological systems and the environment. Such hydrogels could potentially be used as smart materials for the release of active pharmaceuticals or harvesting toxic anions from water and living systems. Here, we demonstrated hydrogel formation utilizing host-guest anion recognition. Using a “decade-old” anion receptor bambus[6]uril, hydrogels were selectively formed in the presence of perchlorate and iodide anions. The presented understanding of the hydrogel structure and exploitation of their dynamic features for the in vitro release of choline derivatives from the hydrogels will help develop smart materials for biomedical or environmental applications. Hydrogelation triggered by host-guest anion recognition is difficult to achieve due to the challenging anion recognition in water and de novo gelator design. Herein, we report such a hydrogel system, based on bambus[6]uril anion receptor, BU. Albeit not a gelator per se, BU formed hydrogels selectively in the presence of iodides or perchlorates. Anion recognition by BU governed the hydrogelation, indicated by the NMR, ATR-IR, and single-crystal X-ray. Gelation mechanism and lamellar nature of the network structure were elucidated by SAXS, cryoSEM, and holotomography methods. Rheological characterization revealed the hydrogels were stable and relatively strong. In physiological saline solutions, the hydrogels released cationic cargo by cation metathesis, leading to a gel-to-gel transformation. Choline derivatives, as model drugs, exhibited slow release from the hydrogels. Our simple hydrogel system may inspire the design of smart materials based on host-guest anion recognition, where the release or sequestration of specific charged species are desirable. Hydrogelation triggered by host-guest anion recognition is difficult to achieve due to the challenging anion recognition in water and de novo gelator design. Herein, we report such a hydrogel system, based on bambus[6]uril anion receptor, BU. Albeit not a gelator per se, BU formed hydrogels selectively in the presence of iodides or perchlorates. Anion recognition by BU governed the hydrogelation, indicated by the NMR, ATR-IR, and single-crystal X-ray. 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Herein, we report hydrogel formation triggered via host-guest anion recognition, utilizing a macrocyclic bambusuril anion receptor, where selective hydrogelation is evident only in the presence of iodide or perchlorate anions. Using a variety of analytical methods, we undoubtedly show anion recognition is the driving force for the formation of stable and strong supramolecular hydrogels, which exhibit lamellar structure of the hydrogel network. We demonstrate that the cations from the supramolecular hydrogels can exchange with cations from solution via cation metathesis, leading to a gel-to-gel transformation. We use this dynamic component-exchange feature to facilitate the release of model cationic drugs, choline derivatives, from the hydrogels at physiological NaCl concentrations. Hydrogels are composed of the macrocyclic dodecamethylbambus[6]uril anion receptor62Svec J. Necas M. Sindelar V. Bambus[6]uril.Angew. Chem. Int. Ed. Engl. 2010; 49: 2378-2381https://doi.org/10.1002/anie.201000420Crossref PubMed Scopus (185) Google Scholar,63Svec J. Dusek M. Fejfarova K. Stacko P. Klán P. Kaifer A.E. Li W. Hudeckova E. Sindelar V. Anion-free Bambus[6]uril and its supramolecular properties.Chemistry. 2011; 17: 5605-5612https://doi.org/10.1002/chem.201003683Crossref PubMed Scopus (76) Google Scholar (BU) and iodide (or perchlorate) salts (Figure 1). The gels were prepared by shortly sonicating the insoluble BU, 1% to 5% (≈ 10 to 50 mM) in the aqueous salt solutions, 50 or 100 mM, respectively (see supplemental information for details). Various (in)organic bio-relevant counter ions of iodide salts, including Li, Na, K, ammonium, tetramethylammonium (TMA), choline (Ch), and acetylcholine (AcCh), successfully formed hydrogels. The minimum gelling concentration for iodide and perchlorate salts was found ≈ 0.8% (≈ 8 mM) of BU by weight at 50 mM of the salt. Higher salt concentrations (> 200 mM) resulted in viscous material, which could turn hydrogel by increasing the BU content to 5%. Lower salt concentrations (< 30 mM), however, did not lead to hydrogelation, regardless of the BU content. The prepared hydrogels were translucent to opaque (Figures 1 and S24), and the self-supporting gel nature (up to 99% of water) was evident in the absence of flow upon vial inversion. Most hydrogels were stable for many months at ambient temperature in a closed vial. The Li, TMA, and AcCh iodide hydrogels tending to precipitate within days or months, depending on the composition (see supplemental information for details). Due to a greater biological significance, the focus of investigations herein was on iodide-derived hydrogels rather than perchlorate. Bambusurils are known to bind anions in the center of their cavity.62Svec J. Necas M. Sindelar V. Bambus[6]uril.Angew. Chem. Int. Ed. 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Int. Ed. Engl. 2015; 54: 276-279https://doi.org/10.1002/anie.201409895Crossref PubMed Scopus (151) Google Scholar Higher anion affinities usually result in solubilization of the water-insoluble BU. Therefore, we assessed the quantity of dissolved anion complexed BU in the presence of different salts in D2O by 1H NMR spectroscopy. Iodide and perchlorate showed proportional linear increase of BU concentration with increasing salt concentration (Figures S25–S32). From these data, the 1:1 association constant for iodide and perchlorate BU complexes in water could be determined as 1.7 × 103 and 1.3 × 103 M−1, respectively (Table S3). In contrast, other sodium salts (Cl−, Br−, BF4−, PF6−, NO3−, IO4−) exhibited poor solubilization of the BU, also indicating very weak anion binding (Table S2). Only up to 0.3 mM of BU was dissolved at 200 mM of these salts. This is the amount of BU that NaI or NaClO4 can dissolve at only 10 mM. In the case of NaCl, no BU was detected in the solution, indicating that chlorides are not bound at all by the BU in water. The observed differences in BU solubilization between the gelling and non-gelling salt systems strongly suggest that the dissolution of BU upon anion complexation is an important step in the hydrogel formation, in agreement with the observed selectivity. Although BU binds anions in solution with a 1:1 stoichiometry, the composition of the solid-state hydrogel network could differ from that of solution. The composition of the hydrogel network (i.e., salt:BU ratio) was, therefore, investigated by the 1H NMR. Hydrogels comprising 50 mM BU and 100 mM ChI, AcChI, or TMAI were placed in D2O for 10, 20, 30, and 60 min. Then the surrounding solution was removed, the hydrogels were completely dissolved in 50-mM NaCl D2O/CD3CN, and the cation:BU ratio was determined by 1H NMR. Slower diffusion is expected for the salt incorporated into the hydrogel network via BU anion binding in comparison with the salt in the entrapped liquid phase (Figure 2). Thus, with increasing time the hydrogels spent in D2O, the remaining salt/BU ratio is indicative of the hydrogel network composition. The NMR experiment strongly suggested the 1:1 salt/BU composition of the hydrogel network, further supporting the frequently observed 1:1 anion binding to BU.62Svec J. Necas M. Sindelar V. Bambus[6]uril.Angew. Chem. Int. Ed. Engl. 2010; 49: 2378-2381https://doi.org/10.1002/anie.201000420Crossref PubMed Scopus (185) Google Scholar,63Svec J. Dusek M. Fejfarova K. Stacko P

Construction of C-C bonds via photoreductive coupling of ketones and aldehydes in the metal-organic-framework MFM-300(Cr)

Construction of C-C bonds via reductive coupling of aldehydes and ketones is hindered by the highly negative reduction potential of these carbonyl substrates, particularly ketones, and this renders the formation of ketyl radicals extremely endergonic. Here, we report the efficient activation of carbonyl compounds by the formation of specific host-guest interactions in a hydroxyl-decorated porous photocatalyst. MFM-300(Cr) exhibits a band gap of 1.75 eV and shows excellent catalytic activity and stability towards the photoreductive coupling of 30 different aldehydes and ketones to the corresponding 1,2-diols at room temperature. Synchrotron X-ray diffraction and electron paramagnetic resonance spectroscopy confirm the generation of ketyl radicals via confinement within MFM-300(Cr). This protocol removes simultaneously the need for a precious metal-based photocatalyst or for amine-based sacrificial agents for the photochemical synthesis.

Geometry control of adsorption sites in sulfonate-pillared hybrid ultramicroporous materials for efficient C4 olefin separations

Efficient isolation of C4 olefins is of paramount importance in petrochemical industry yet a challenging task mainly realized via heat-driven processes owing to their similar physical properties. Herein, sulfonate anion-pillared hybrid ultramicroporous materials (HUMs), namely TMOF-1 and ZU-619 (BDS-1-Cu-i) were reported for the first time for the efficient separation of ternary C4 olefin mixtures (C4H6/n-C4H8/iso-C4H8). The geometry of adsorption sites was judiciously controlled via tuning the interpenetration direction of sulfonate anions through varying the length of anions. Interestingly, ethanedisulfonate anions in TMOF-1 exhibit the vertically interpenetrated direction, leading to TMOF-1 with pore size of 4.5 Å to exclude iso-C4H8. Furthermore, the vertical interpenetration makes the adjacent anions behave as synergetic adsorption sites for n-C4H8 and C4H6 trapping, thus endowing TMOF-1 with strong host–guest interactions and the benchmark Henry coefficient separation selectivities for C4H6/iso-C4H8 (519.2) and n-C4H8/iso-C4H8 (93.2) mixtures. In contrast, ZU-619 with butanedisulfonate anions as pillars exhibits normal interpenetration framework, giving rise to the anion-restricted pore size of 9.4 Å. This large pore size results in ZU-619 with weak host–guest interactions for C4 olefins through one sulfate anion. The specific host–guest interaction modes were unveiled by molecular simulations, presenting the efficiency of binding site geometry control for gas separation. The separation efficiency was confirmed by breakthrough experiments, the results presented that TMOF-1 showed excellent separation performances for C4H6/n-C4H8/iso-C4H8 mixtures and ZU-619 can be a good candidate for C4H6/n-C4H8 separation.