Selective Host Guest Research Articles

Electrochemical behavior of novel electroactive LaTi4Mn3O12/polyaniline composite for Li+-ion recovery from brine with high selectivity

With the increase in worldwide consumption of lithium owing to its use in electronic devices, it is necessary to develop less energy-intensive alternatives for Li production to meet its rapidly growing demand. Electrochemical Li harvesting is a simple approach that can complement existing extraction technologies. However, its effectiveness depends on the design of highly efficient electrodes that can preferentially adsorb Li ions in the presence of abundant interfering cations while exhibiting low energy consumption. Herein, we report the synthesis of delithiated LiLaTi4Mn3O12 (LTMO) as a novel electrode material for the effective recovery of Li+ ions from brine. The introduced LTMO/polyaniline (PANI) composite electrode exhibited excellent Li+-ion selectivity, high water stability, and rapid regeneration. The fast intercalation of Li+ ions was attributable to the presence of highly conductive Mn3+ ions along the A-sites and nanopores with suitable diameters for selective host–guest Li extraction. Under optimal conditions (potential = 0.5 V), PANI/LTMO exhibited a Li adsorption capacity as high as 38.7 mg/g after 60 min and a desorption ratio of 98.5 % when the current was reversed. Moreover, the delithiated electrode exhibited selectivity coefficients of 88.5 and 52.5 for Li+/Na+ and Li+/Mg2+ binary solutions, respectively. The PANI/LTMO electrode exhibited faster Li+-ion intercalation/deintercalation while using a small amount of energy and thus has immense potential for use in high-throughput electrodes for effective lithium extraction from seawater.

Oxidation of sodium cholate catalyzed by Au NPs and chiral selective binding of R- and S-binaphthyl derivatives

Au NPs generated in situ by photochemical reduction method were used as catalysts for the oxidation of sodium cholate. The circular dichroism of the oxidation product of sodium cholate exhibits a positive Cotton effect at 335 nm and an intense negative Cotton effect at 281 nm. Electrospray ionization (ESI) mass spectra and nuclear magnetic resonance (NMR) spectra were performed to characterize the chemical composition of the oxidation product of sodium cholate, revealing that two of the hydroxyl groups were selectively oxidized to oxo groups and the oxidation product is 12-hydroxy-3,7-diketo-cholanic acid (3,7-DKCA). The chiral recognition abilities of the aggregates of 3,7-DKCA were investigated by using planar chiral molecules R- and S-binaphthyl compounds. Compared with sodium cholate, the aggregates of 3,7-DKCA displayed higher chiral selective host–guest binding to the model molecules and the chiral recognition mechanism was clarified.

Highly selective detection of TNP over other nitro compounds in water: the role of selective host–guest interactions in Zr-NDI MOF

A fluorescent Zr-NDI based MOF shows the selective sensing of TNP in water, over other classes of nitro compounds. DFT studies reveal favourable host–guest interactions behind this phenomenon.

A pillar[5]arene-based covalent organic framework with pre-encoded selective host-guest recognition.

It is highly desirable to maintain both permanent accessible pores and selective molecular recognition capability of macrocyclic cavitands in the solid state. Integration of well-defined discrete macrocyclic hosts into ordered porous polymeric frameworks (e.g., covalent organic frameworks, COFs) represents a promising strategy to transform many supramolecular chemistry concepts and principles well established in the solution phase into the solid state, which can enable a broad range of practical applications, such as high-efficiency molecular separation, heterogeneous catalysis, and pollution remediation. However, it is still a challenging task to construct macrocycle-embedded COFs. In this work, a novel pillar[5]arene-derived (P5) hetero-porous COF, denoted as P5-COF, was rationally designed and synthesized. Featuring the unique backbone structure, P5-COF exhibited selective adsorption of C2H2 over C2H4 and C2H6, as well as significantly enhanced host–guest binding interaction with paraquat, in comparison with the pillar[5]arene-free COF analog, Model-COF. The present work established a new strategy for developing COFs with customizable molecular recognition/separation properties through the bottom-up “pre-porous macrocycle to porous framework” design.

Harnessing host–guest interactions to control structure at the nanoscale

Abstract Host–guest interactions mediate many chemical and biochemical transformations and are extensively exploited in a number of industrially-relevant chemical processes. Many porous inorganic (e.g., zeolite) and molecular (e.g., metal-organic framework) hosts engage reagents in their environment through selective host–guest interactions. While researchers frequently capitalize on host–guest interactions to sequester chemical species or to catalyze reactions, these interactions can also be used to direct nanomaterial synthesis. In this Perspective we highlight the promise and opportunities for harnessing host–guest interactions to control the structure and dimensionality of materials. We focus our discussion on emerging strategies in soft chemistry and promising new directions which use porous ionic solids to direct the growth of complex nanoscale dimers and Janus nanoparticles.

Selective host-guest chemistry, self-assembly and conformational preferences of m-xylene macrocycles probed by ion-mobility spectrometry mass spectrometry.

We demonstrated ion-mobility spectrometry mass spectrometry (IMS-MS) as a powerful tool for interrogating and preserving selective chemistry including non-covalent and host-guest complexes of m-xylene macrocycles formed in solution. The technique readily revealed the unique favorability of a thiourea-containing macrocycle MXT to Zn2+ to form a dimer complex with the cation in an off-axis sandwich structure having the Zn-S bonds in a tetrahedral coordination environment. Replacing thiourea with urea generates MXU which formed high-order oligomerization with weak binding interactions to neutral DMSO guests detected at every oligomer size. The self-assembly pathway observed for this macrocycle is consistent with the crystalline assembly. Further transformation of urea into squaramide produces MXS, a rare receptor for probing sulfate in solution. Tight complexes were observed for both monomeric and dimeric of MXS in which HSO4- bound stronger than SO42- to the host. The position of HSO4- at the binding cavity is a 180° inversion of the reported crystallographic SO42-. The MXS dimer formed a prism-like shape with HSO4- exhibiting strong contacts with the 8 amine protons of two MXS macrocycles. By eliminating intermolecular interferences, we detected the low energy structures of MXS with collisional cross section (CCS) matching cis-trans and cis-cis squaramides-amines, both were not observed in crystallization trials. The experiments collectively unravel multiple facets of macrocycle chemistry including conformational flexibility, self-assembly and ligand binding; all in one analysis. Our findings illustrate an inexpensive and widely applicable approach to investigate weak but important interactions that define the shape and binding of macrocycles.

Controllable emulsion phase behaviour via the selective host-guest recognition of mixed surfactants at the water/octane interface

Emulsions are deeply involved in almost all aspects of the petroleum industry, especially in enhanced oil recovery. Supramolecular chemistry proposes a facile and controllable method to construct target assemblies. In this report, we investigated the effects of β-cyclodextrin (β-CD) on the emulsions stabilized by the mixed N-dodecyl-N-methylpyrrolidinium bromide (L12) and sodium dodecyl sulfate (SDS). The additional β-CD exerted strong influences on the water/n-octane interfacial tension (IFT) between n-octane and the mixed L12/SDS aqueous solutions, which should be attributed to its selective host-guest recognition. Interestingly, the additional β-CD in moderate concentrations could selectively remove the major surfactant molecules at the interface to adjust the hydrophilic-lipophilic balance of the mixed adsorption layers, thereby causing the transformation of the emulsion type from O/W to W/O. The addition of excess β-CD would generate the construction of n-octane/β-CD complexes to enhance the hydrophilicity of the interfacial layers, which leads again to phase inversion. Emulsions and their types were characterized and confirmed by the measurements of their conductivities, average droplet radii and rheological properties. To verify the proposed mechanism for the multiple phase inversion, the effects of L12/SDS molar ratios and β-CD concentrations were studied in depth in the control experiments.

Tuning the aggregation of an amphiphilic anionic calix[5]arene by selective host–guest interactions with bola-type dications

Bola-type dications of different length drive the formation of head-to-tail or capsular supramolecular amphiphiles and, in turn, that of the final aggregates.

Functionalized N-doped graphene quantum dots for electrochemical determination of cholesterol through host-guest inclusion.

Functionalized nitrogen-doped graphene quantum dots (N-GQD) with mean particle size of 8.5 ± 0.5nm were covalently linked to β-cyclodextrin (β-CD) to form a β-CD@N-GQD nanoprobe. The probe is shown to enable voltammetric determination of cholesterol via selective host-guest recognition and by using ferrocene (FC) as the redox indicator.FC is first included inβ-cyclodextrin. Cholesterol has ahigher affinity for β-CD (in comparison to FC). It forms a strong inclusion complex with β-CD and can replace FC from its cavities. The quantity of released FC is proportional to the concentration of cholesterol. The differential pulse voltammetric signal for FC (with a peak at typically 0.22V vs Ag/AgCl) increases linearly in the 0.5-100μM cholesterol concentration range, with a limit of detection as low as 80nM. The assay is found to be highly selective over 15 potentially interfering species. The method was successfully applied to the detection of cholesterol in spiked serum samples which gave recoveries between 96 and 101%. The probe can be stored for at least 28days after which the activity still is 87%. Graphical abstract This scheme illustrates the detection of cholesterol by differential pulse voltammetry (DPV) technique. The β-cyclodextrin functionalized nitrogen-doped graphene quantum dot (β-CD@N-GQD) probe was developed to enable voltammetric determination of cholesterol using selective host-guest recognition.

The improvement of the cationic/anionic surfactant interfacial activity via the selective host-guest recognition

Supramolecular chemistry proposed a controllable and convenient approach to construct the desired complexes used in various fields, including chemical enhanced oil recovery. β‑cyclodextrin (β-CD) can effectively enclose the surfactants to fabricate the stable inclusion complexes via the host-guest recognition. In the present report, the β‑CD effects on the interfacial activities of the mixed surfactant system consisting of N‑dodecyl‑N‑methylpyrrolidinium bromide (L12) and sodium dodecyl sulfate (SDS) were systematically evaluated. Interestingly, the additional β-CD molecules greatly reduced the interfacial tension (IFT) between the L12/SDS aqueous solution and model oil (toluene and n-decane, v/v = 1:1). Due to the electrostatic attraction of L12/SDS, the β-CD molecules could selectively enclose the majority surfactants to improve the intensive arrangements of mixed surfactants at the interface. In general, the host-guest recognition facilitates the fabrications of β-CD/surfactant inclusions and decrease surfactant interfacial concentrations. The competition between the host-guest recognition and the electrostatic attraction dominates the IFT variations. Then we changed the molar ratio of L12/SDS, the dissolved order of chemicals and explored the variations of the mixed surfactants hydrophile-lipophile balance to further confirm the proposed mechanism. Moreover, the salinity and temperature effects on the IFT were systematically investigated.

A crab claw shaped molecular receptor for selective recognition of picric acid: supramolecular self-assembly mediated aggregation induced emission and color change

2,6-Pyridine bis(iminoantipyrine) (PyBAP), a crab claw shaped open neutral molecular receptor with multiple non-covalent sites, showed selective recognition of picric acid (PA) through supramolecular interactions that lead to an intermolecular charge transfer induced naked-eye detectable color change both in solution as well as in the solid state and rare turn-on solid state fluorescence. The selective host–guest formation of PyBAP–PA has been confirmed using 1H-NMR, single crystal structural analysis and computational studies.

Selective Host–Guest Co‐crystallization of Pyridine‐Functionalized Tetraphenylethylenes with Phthalic Acids and Multicolor Emission of the Co‐crystals

Tetraphenylethylene (TPE) and its derivatives are the most typical and most widely studied organic compounds showing aggregation-induced emission (AIE). Due to their propeller-like structures, V-like clefts exist between the aryl rings, which make them promising host compounds. However, such a possibility is seldom explored. Herein, it is reported that TPE derivatives bearing two or four pyridine rings at the para positions of the phenyl rings (TPE-Pys) can selectively include triangular (Δ-like) m-phthalic acid from a mixture of o-, m-, and p-phthalic acids due to their shape complementary to form host-guest co-crystals, which showed redder emission than the TPE-Pys themselves. The emission of co-crystals 1-5 could be reversibly switched between yellow and red by alternating exposure to HCl and ammonia vapor. The host-guest co-crystals not only exhibited great potential for selectively recognizing and separating m-phthalic acid and as multicolor emission materials, but are also suitable for use as secret ink due to their reversible color change on varying the host-guest interactions.

Novel Water-Soluble Cyclodextrin-Based Conjugated Polymer for Selective Host–Guest Interactions of Cationic Surfactant CTAB and Reverse FRET with Rhodamine B Tagged Adamantyl Guest

A new water-soluble π-conjugated main-chain polymer P1 bearing a β-cyclodextrin (β-CD) pendant was designed and synthesized. The aggregation and disaggregation of P1 generated faded yellow-greenish and bright-yellow emissions, respectively. The inclusion complexation capability of P1 through β-CD pendant with a cationic surfactant cetyltrimethylammonium bromide (CTAB) guest and associative interactions of P1 with Fe3+ through triazole spacers resulted in significantly enhanced and completely diminished emission profiles of P1 in pure water, respectively. Interestingly, ADRhB as another rhodamine B (RhB) tagged adamantyl guest was transformed into ADRhB(O), i.e., the open form of ADRhB, to generate RhB emission in the presence of Fe3+ ion selectively for the pendent host β-CD of P1, and the further interaction of ADRhB(O)/Fe3+ with P1 prevailed a completely quenched RhB emission via the inclusion complexation of adamantyl terminal of ADRhB(O) in β-CD. Moreover, stronger interactions of CTAB with β-CD further generated RhB emission of ADRhB(O) even in the presence of acceptor P1. Finally, a novel β-CD bearing water-soluble P1 with selective and strong interactions of CTAB toward disaggregation events in pure water, and further electrostatic repulsion and utilization of RhB via RhB-tagged adamantyl guest ADRhB(O) as a donor revealed the reverse-fluorescence resonance energy transfer (FRET) process of P1.

Solution vs. gas phase relative stability of the choline/acetylcholine cavitand complexes.

How the information obtained from the gas phase experiments can reflect the processes in solution is a crucial question for analytical chemistry, and particularly the selective host-guest recognition mechanisms which are fundamental in biology. Here we combine ElectroSpray Ionization mass spectrometry (ESI-MS) and the Collision Induced Dissociation (CID) experiments to the density functional theory to investigate the interaction of acetylcholine and the choline cation with a triphosphonate cavitand. While the relative abundance of the cation complexes in the ESI mass spectrum reflects the preferential capture of the acetylcholine ion over the choline ion by the cavitand in the solution, the gas phase CID measurements indicate that after desolvation the choline cation is the most strongly bound to the host. The experimental results are interpreted by theory that underlines the role of the counterion in the stabilization of the complexes in solution and therefore in the selective recognition of substrates of biological interest.

β-Cyclodextrin coated CdSe/ZnS quantum dots for vanillin sensoring in food samples

An optical sensor for vanillin in food samples using CdSe/ZnS quantum dots (QDs) modified with β-cyclodextrin (β-CD) was developed. This vanillin-sensor is based on the selective host–guest interaction between vanillin and β-cyclodextrin. The procedure for the synthesis of β-cyclodextrin–CdSe/ZnS (β-CD–CdSe/ZnS-QDs) complex was optimized, and its fluorescent characteristics are reported. It was found that the interaction between vanillin and β-CD–CdSe/ZnS-QDs complex produced the quenching of the original fluorescence of β-CD–CdSe/ZnS-QDs according to the Stern–Volmer equation. The mechanism of the interaction is discussed. The analytical potential of this sensoring system was demonstrated by the determination of vanillin in synthetic and food samples. The method was selective for vanillin, with a limit of detection of 0.99µgmL−1, and a reproducibility of 4.1% in terms of relative standard deviation (1.2% under repeatability conditions). Recovery values were in the 90–105% range for food samples.

Polymer Brushes Exhibiting Versatile Supramolecular Interactions Grown by Nitroxide-Mediated Polymerization and Structured via Microcontact Chemistry

Functionalization of metal, glass, and semiconductor substrates with polymers and nanoparticles is a key challenge for surface-based material science. Such substrates have the potential to find widespread application in optical and electronic devices, microarrays, and materials for information storage. We report site-specific immobilization of nitroxide-mediated polymerization initiators via microcontact chemistry employing thiol–ene click chemistry on glass-supported alkene-terminated self-assembled monolayers. The polymer initiator covered substrates are used for preparation of poly(styrene) and poly(acrylate) brushes with defined and tunable brush thicknesses. Brush thickness dependent site-specific protein adsorption of streptavidin and concanavalin A on structured polystyrene brushes is reported. Poly(styrene) brushes with a thickness of 40 nm or larger showed protein repellence whereas brushes below 15 nm thickness reveal protein adhesive properties. We also disclose the site selective host–guest assisted immobilization of β-cyclodextrin-coated silica nanoparticles and the tethering of liposomes modified with amphiphilic β-cyclodextrin onto adamantane-functionalized poly(acrylate) brushes. Selective immobilization of these supramolecular colloids via the multivalent hydrophobic inclusion complex of β-cyclodextrin and adamantane can be readily verified by fluorescence microscopy imaging, atomic force microscopy, and quartz crystal microbalance with dissipation monitoring.

Selective Host–Guest Interactions of a Transformable Coordination Capsule/Tube with Fullerenes

AbstractAn M2L4 coordination capsule or an M2L2 coordination tube was selectively formed by the combination of HgII hinges and bent bispyridine ligands. The two structures reversibly interconvert at room temperature in response to modulation of the metal‐to‐ligand ratio and exhibit different host–guest interaction behavior. The capsule alone encapsulates large spherical molecules, fullerenes C60 and C70, and the bound guests are released upon capsule‐to‐tube transformation by the simple addition of metal ions.

Selective Host–Guest Interactions of a Transformable Coordination Capsule/Tube with Fullerenes

An M2L4 coordination capsule or an M2L2 coordination tube was selectively formed by the combination of Hg(II) hinges and bent bispyridine ligands. The two structures reversibly interconvert at room temperature in response to modulation of the metal-to-ligand ratio and exhibit different host-guest interaction behavior. The capsule alone encapsulates large spherical molecules, fullerenes C60 and C70, and the bound guests are released upon capsule-to-tube transformation by the simple addition of metal ions.

Identifying Selective Host–Guest Interactions Based on Hydrogen Bond Donor–Acceptor Pattern in Functionalized Al-MIL-53 Metal–Organic Frameworks

We present a study analyzing the selectivity of host–guest interactions in a series of functionalized Al-MIL-53-X metal–organic frameworks with X = H, NH2, and NHCHO using acetone, ethanol, and water as probe molecules. While the amino group introduces additional hydrogen bond donor centers the NHCHO anchors function as donor and acceptor. The guests were chosen due to their ability to act solely as an acceptor in the case of acetone, whereas ethanol and water provide acceptor and donor qualities with a gradual decrease of the acceptor strength toward ethanol. The characterization of the host–guest interactions includes a comprehensive solid-state NMR spectroscopic study based on a full assignment of 1H and 13C high-resolution spectra using CRAMPS decoupling schemes to enhance 1H resolution combined with advanced 2D HETCOR (1H–13C, 1H–27Al, and 1H–14N) spectra at high magnetic fields. In spite of a pronounced dynamical disorder of the guests, we could identify a preferred binding of the acetone via a NH··...

In Situ Supramolecular Assembly and Modular Modification of Hyaluronic Acid Hydrogels for 3D Cellular Engineering

A facile in situ supramolecular assembly and modular modification of biocompatible hydrogels were demonstrated using cucurbit[6]uril-conjugated hyaluronic acid (CB[6]-HA), diaminohexane-conjugated HA (DAH-HA), and tags-CB[6] for cellular engineering applications. The strong and selective host-guest interaction between CB[6] and DAH made possible the supramolecular assembly of CB[6]/DAH-HA hydrogels in the presence of cells. Then, the 3D environment of CB[6]/DAH-HA hydrogels was modularly modified by the simple treatment with various multifunctional tags-CB[6]. Furthermore, we could confirm in situ formation of CB[6]/DAH-HA hydrogels under the skin of nude mice by sequential subcutaneous injections of CB[6]-HA and DAH-HA solutions. The fluorescence of modularly modified fluorescein isothiocyanate (FITC)-CB[6] in the hydrogels was maintained for up to 11 days, reflecting the feasibility to deliver the proper cues for cellular proliferation and differentiation in the body. Taken together, CB[6]/DAH-HA hydrogels might be successfully exploited as a 3D artificial extracellular matrix for various tissue engineering applications.