Cationic Guests Research Articles

Atomic-Scale Imaging of Clay Mineral Nanosheets and Their Supramolecular Complexes through Electron Microscopy: A Supramolecular Chemist's Perspective.

Recent advancements in electron microscopy techniques have revolutionized the ability to directly visualize and understand the intricate world of supramolecular chemistry. This paper provides a concise overview of a study delving into the atomic-scale imaging of monolayer clay mineral nanosheets and their associated supramolecular complexes. The imaging is conducted by harnessing the power of aberration-corrected scanning transmission electron microscopy (STEM). Clay mineral nanosheets, with their anionic charge and ultrathin thickness (of 1 nm), serve as a stable Coulombic host material for cationic guest molecules through electrostatic interactions, facilitating exceptional stability and control during observation. By incorporation of heavy-metal atom markers coordinated within the target molecules, high-angle annular dark field STEM enables a clear visualization of these supramolecular complexes. This approach helps to overcome the limitations of graphene-based systems and expands the possibilities of atomic-scale imaging of nonperiodic molecular assemblies formed by weak supramolecular interactions. The fusion of electron microscopy techniques with the principles of supramolecular and material chemistry offers exciting opportunities for studying the structure, behavior, and properties of complex supramolecular systems. It sheds light on the intricate molecular architectures and design principles governing these systems. This study showcases the immense potential of electron microscopy in supramolecular chemistry and invites researchers from various disciplines to explore the transformative possibilities of atomic-scale imaging in the field.

Planar Polymer Membranes Accommodate Functional Self-Assembly of Inserted Resorcinarene Nanocapsules.

Solid-supported polymer membranes (SSPMs) offer great potential in material and life sciences due to their increased mechanical stability and robustness compared to solid-supported lipid membranes. However, there is still a need for expanding the functionality of SSPMs by combining them with synthetic molecular assemblies. In this study, SSPMs served as a flexible matrix for the insertion of resorcinarene monomers and their self-assembly into functional hexameric resorcinarene capsules. Resorcinarene capsules provide a large cavity with affinity specifically for cationic and polyhydroxylated molecules. While the capsules are stable in apolar organic solvents, they disassemble when placed in polar solvents, which limits their application. Here, a solvent-assisted approach was used for copolymer membrane deposition on solid support and simultaneous insertion of the resorcinarene monomers. By investigation of the molecular factors and conditions supporting the codeposition of the copolymer and resorcinarene monomers, a stable hybrid membrane was formed. The hydrophobic domain of the membrane played a crucial role by providing a sufficiently thick and apolar layer, allowing for the self-assembly of the capsules. The capsules were functional inside the membranes by encapsulating cationic guests from the aqueous environment. The amount of resorcinarene capsules in the hybrid membranes was quantified by a combination of quartz-crystal microbalance with dissipation and liquid chromatography-mass spectrometry, while the membrane topography and layer composition were analyzed by atomic force microscopy and neutron reflectometry. Functional resorcinarene capsules inside SSPMs can serve as dynamic sensors and potentially as cross-membrane transporters, thus holding great promise for the development of smart surfaces.

Enhancing Hydrogen Evolution Reaction Activity of Palladium Catalyst by Immobilization on MXene Nanosheets.

Efficient catalysts with minimal content of catalytically active noble metals are essential for the transition to the clean hydrogen economy. Catalyst supports that can immobilize and stabilize catalytic nanoparticles and facilitate the supply of electrons and reactants to the catalysts are needed. Being hydrophilic and more conductive compared with carbons, MXenes have shown promise as catalyst supports. However, the controlled assembly of their 2D sheets creates a challenge. This study established a lattice engineering approach to regulate the assembly of exfoliated Ti3C2Tx MXene nanosheets with guest cations of various sizes. The enlargement of guest cations led to a decreased interlayer interaction of MXene lamellae and increased surface accessibility, allowing intercalation of Pd nanoparticles. Stabilization of Pd nanoparticles between interlayer-expanded MXene nanosheets improved their electrocatalytic activity. The Pd-immobilized K+-intercalated MXene nanosheets (PdKMX) demonstrated exceptional electrocatalytic performance for the hydrogen evolution reaction with the lowest overpotential of 72 mV (@10 mA cm-2) and the highest turnover frequency of 1.122 s-1 (@ an overpotential of 100 mV), which were superior to those of the state-of-the-art Pd nanoparticle-based electrocatalysts. Weakening of the interlayer interaction during self-assembly with K+ ions led to fewer layers in lamellae and expansion of the MXene in the c direction during Pd anchoring, providing numerous surface-active sites and promoting mass transport. In situ spectroscopic analysis suggests that the effective interfacial electron injection from the Pd nanoparticles strongly immobilized on interlayer-expanded PdKMX may be responsible for the improved electrocatalytic performance.

Multiple Cations Nanoconfinement in Ultrathin V2 O5 Nanosheets Enables Ultrafast Ion Diffusion Kinetics Toward High-performance Zinc Ion Battery.

Nanoconfinement of cations in layered oxide cathode is an important approach to realize advanced zinc ion storage performance. However, thus far, the conventional hydrothermal/solvothermal route for this nanoconfinement has been restricted to its uncontrollable phase structure and the difficulty on the multiple cation co-confinement simultaneously. Herein, this work reports a general, supramolecular self-assembly of ultrathin V2 O5 nanosheets using various unitary cations including Na+ , K+ , Mg2+ , Ca2+ , Zn2+ , Al3+ , NH4 + , and multiple cations (NH4 + + Na+ , NH4 + + Na+ + Ca2+ , NH4 + + Na+ + Ca2+ +Mg2+ ). The unitary cation confinement results in a remarkable increase in the specific capacity and Zn-ion diffusion kinetics, and the multiple cation confinement gives rise to superior structural and cycling stability by multiple cation synergetic pillaring effect. The optimized diffusion coefficient of Zn-ion (7.5 × 10-8 cm2 s-1 ) in this assembly series surpasses most of the V-based cathodes reported up to date. The work develops a novel multiple-cations nanoconfinement strategy toward high-performance cathode for aqueous battery. It also provides new insights into the guest cation regulation of zinc-ion diffusion kinetics through a general, supramolecular assembly pathway.

Polysulfonated covalent organic framework as active electrode host for mobile cation guests in electrochemical soft actuator

Tailoring transfer dynamics of mobile cations across solid-state electrolyte-electrode interfaces is crucial for high-performance electrochemical soft actuators. In general, actuation performance is directly proportional to the affinity of cations and anions in the electrolyte for the opposite electrode surfaces under an applied field. Herein, to maximize electrochemical actuation, we report an electronically conjugated polysulfonated covalent organic framework ( p S-COF) used as a common electrolyte-electrode host for 1-ethyl-3-methylimidazolium cation embedded into a Nafion membrane. The p S-COF–based electrochemical actuator exhibits remarkable bending deflection at near-zero voltage (~0.01 V) and previously unattainable blocking force, which is 34 times higher than its own weight. The ultrafast step response shows a very short rising time of 1.59 seconds without back-relaxation, and substantial ultralow-voltage actuation at higher frequencies up to 5.0 hertz demonstrates good application prospects of common electrolyte-electrode hosts. A soft fluidic switch is constructed using the proposed soft actuator as a potential engineering application.

Hydro‐Photo‐Thermo‐Responsive Multicolor Luminescence Switching of a Ternary MOF Hybrid for Advanced Information Anticounterfeiting

AbstractDeveloping smart materials capable of solid‐state multicolor photoluminescence (PL) switching in response to multistimuli is highly desirable for advanced anticounterfeiting. Here, a ternary MOF hybrid showing hydro‐photo‐thermo‐responsive multicolor PL switching in the solid state is presented. This hybrid is constructed by co‐immobilizing Eu3+ and methyl viologen (MV) cations within an anionic MOF via the cation‐exchange approach. The confined guest cations are well arranged in the framework channels, facilitating the synergistic realization of stimuli‐responsive multiple PL color‐switching through intermolecular coupling. The hybrid undergoes a rapid and reversible PL color‐switching from red to blue upon water simulation, which is achieved by activating the blue emission of the framework linker while simultaneously quenching the Eu3+ emission. Furthermore, the hybrid displays photo‐thermo‐responsive PL switching from red to dark. UV‐light irradiation or heating triggers the chromic conversion of MV to its colored radical form, which exhibits perfect spectral overlap with Eu3+, thus activating Förster resonance energy transfer (FRET) from Eu3+ to MV radicals and quenching the Eu3+ emission. Inspired by these results, PL morse patterns are designed and fabricated using a novel triple‐level encryption strategy, showcasing the exciting potential of this hybrid in advanced anticounterfeiting applications.

A Ditopic Covalent Cage for Ion-Pair Binding: Influence of Anion Complexation on the Cation Exchange Rate.

A new hemicryptophane host with a ditopic molecular cavity combining a cyclotriveratrylene (CTV) unit with a tris-urea moiety was synthesized. The complexation of halides, tetramethylammonium (TMA+) cation, and ion pairs was investigated. A positive cooperativity was observed, since halides display a higher binding constant when a TMA cation is already present inside the cage. When TMA was complexed alone, a decrease of temperature from 298 K to 230 K was required to switch from a fast to a slow exchange regime on the NMR time scale. Nevertheless, the prior complexation of a halide guest in the lower part of the host resulted in significant decrease of the exchange rate of the subsequent complexation of the TMA+ cation. Under these conditions, the 1H NMR signals characteristic of a slow exchange regime were observed at 298 K. Addition of an excess of salts, increases the ionic strength of the solution, restoring the fast exchange dynamics. This result provides insight on how the exchange rate of a cation guest can be modulated by the complexation of a co-guest anion.

Cation Recognition by Dibenzoarsacrowns

AbstractWe recently reported dibenzoarsacrowns as a novel class of host molecules, and in this work, prepared four dibenzoarsacrowns:12‐dibenzoarsacrown‐4, 15‐dibenzoarsacrown‐5, 18‐dibenzoarsacrown‐6, and 21‐dibenzoarsacrown‐7, and investigated their guest recognition behaviors for alkali metal and ammonium cations (Li+, Na+, K+, and NH4+). It was found that the triphenylarsine moiety of the dibenzoarsacrowns could be electrochemically oxidized and that their oxidation potentials shifted in response to perturbation because of the weak interaction between the arsenic atom and guest cations. Thus, dibenzoarsacrowns could electrochemically detect cations with sizes that fit the host cavity. Electron spin resonance measurements revealed the generation of cation radical species of arsenic under the application of voltage and supported the idea that the interaction between the arsenic atom and guest cations played a crucial role in the detection of cations. In addition, ion chromatography studies showed that size‐selective cation recognition by dibenzoarsacrowns was achievable even in aqueous solutions.

D2/H2 separation by quantum sieving in LiNaA zeolites: the role of aperture size and strong guest–cation interactions

D2/H2 separation by quantum sieving in LiNaA zeolites: the role of aperture size and strong guest–cation interactions

In Situ Photoisomerization of an Azobenzene-Based Triple Helicate with a Prolonged Thermal Relaxation Time.

The phosphate-coordination triple helicates A2 L3 (A=anion) with azobenzene-spaced bis-bis(urea) ligands (L) have proven to undergo a rare in situ photoisomerization (without disassembly of the structure) rather than the typically known, stepwise "disassembly-isomerization-reassembly" process. This is enabled by the structural self-adaptability of the "aniono" assembly arising from multiple relatively weak and flexible hydrogen bonds between the phosphate anion and bis(urea) units. Notably, the Z→E thermal relaxation rate of the isomerized azobenzene unit is significantly decreased (up to 20-fold) for the triple helicates compared to the free ligands. Moreover, the binding of chiral guest cations inside the cavity of the Z-isomerized triple helicate can induce optically pure diastereomers, thus demonstrating a new strategy for making light-activated chiroptical materials.

In Situ Photoisomerization of an Azobenzene‐Based Triple Helicate with a Prolonged Thermal Relaxation Time

AbstractThe phosphate‐coordination triple helicates A2L3 (A=anion) with azobenzene‐spaced bis‐bis(urea) ligands (L) have proven to undergo a rare in situ photoisomerization (without disassembly of the structure) rather than the typically known, stepwise “disassembly‐isomerization‐reassembly” process. This is enabled by the structural self‐adaptability of the “aniono” assembly arising from multiple relatively weak and flexible hydrogen bonds between the phosphate anion and bis(urea) units. Notably, the Z→E thermal relaxation rate of the isomerized azobenzene unit is significantly decreased (up to 20‐fold) for the triple helicates compared to the free ligands. Moreover, the binding of chiral guest cations inside the cavity of the Z‐isomerized triple helicate can induce optically pure diastereomers, thus demonstrating a new strategy for making light‐activated chiroptical materials.

Catalytic Inhibition of Base-Mediated Reactivity by a Self-Assembled Metal-Ligand Host.

Spacious M4 L6 tetrahedra can act as catalytic inhibitors for base-mediated reactions. Upon adding only 5 % of a self-assembled Fe4 L6 cage complex, the conversion of the conjugate addition between ethylcyanoacetate and β-nitrostyrene catalyzed by proton sponge can be reduced from 83 % after 75 mins at ambient temperature to <1 % under identical conditions. The mechanism of the catalytic inhibition is unusual: the octacationic Fe4 L6 cage increases the acidity of exogenous water in the acetonitrile reaction solvent by favorably binding the conjugate acid of the basic catalyst. The inhibition only occurs for Fe4 L6 hosts with spacious internal cavities: minimal inhibition is seen with smaller tetrahedra or Fe2 L3 helicates. The surprising tendency of the cationic cage to preferentially bind protonated, cationic ammonium guests is quantified via the comprehensive modeling of spectrophotometric titration datasets.

Synthesis and Host-Guest Chemistry of Chiral Spirobifluorene-Based Macrocycles Soluble in Basic Aqueous Solution.

Synthesis and host-guest chemistry of water-soluble (pH 12.5) chiral spirobifluorene-based macrocycles 2-[n] were carried out. Cationic guests, such as quaternary ammonium salts, were accommodated well in the hosts. Cp2Co+ was especially strongly bound in 2-[4] (Ka of up to 3.0 × 105 M-1). Enantioselective recognition with (l)-carnitine was also achieved.

Scalable Synthesis of Pre‐Intercalated Manganese(III/IV) Oxide Nanostructures for Supercapacitor Electrodes: Electrochemical Comparison of Birnessite and Cryptomelane Products

AbstractManganese(III/IV) oxide is a promising pseudocapacitive material for supercapacitor electrodes due to favorable attributes such as its chemical resilience, high earth abundance and low specific cost. Herein, the morphological, compositional and electrochemical characteristics of co‐precipitated manganese(III/IV) oxide products, each described by the general formula NaxKyMnOz, are investigated to establish how these properties are influenced by synthesis conditions. NaxKyMnOz growths in low‐temperature (&lt;100 °C) basic and acidic environments are shown to promote the formation of turbostratic birnessite and cryptomelane phases, respectively, with the latter polymorph containing a relatively low concentration of interstitial Na+ and K+ cations. It is demonstrated that K+ pre‐insertion during synthesis yields lower initial charge‐transfer resistances than equivalent Na+ intercalation, and that this parameter correlates strongly with storage performance. Accordingly, Na‐mediated storage initially delivers inferior specific capacitances and Coulombic efficiencies than K‐based mechanisms, but K+ intercalation/deintercalation causes faster capacitance decay during prolonged galvanostatic cycling. Furthermore, whilst crystallographic phase is shown to have a weaker effect on NaxKyMnOz storage properties than the choice of intercalating guest cations, cryptomelane electrodes are more susceptible to cycling‐induced capacitance and efficiency losses than their birnessite counterparts. In combination, these insights provide an instructive foundation for the optimization of NaxKyMnOz in high‐power storage applications.

Kinetics of base-promoted transformation of berberrubine-cucurbit[7]uril inclusion complex: Active role of alkali cations

A pH-responsive inclusion complex was created from berberrubine, a pharmacological active natural isoquinoline alkaloid and cucurbit[7]uril (CB7) macrocycle exploiting the more than four orders of magnitude larger binding affinity of the cationic guest (BOH+) compared to the deprotonated uncharged conjugate base (BO). Since only the CB7-encapsulated BOH+ emitted strong fluorescence, the transformation of this host–guest complex could be selectively monitored in real time by stopped-flow measurements. Alkali cations accelerated the exit of BOH+ from the CB7 cavity in a pseudo-first order reaction and their impact grew with the ion radius. In contrast, the gradual rise of alkali hydroxide concentration brought about parabolic increase in the apparent rate constant of the deprotonation of the CB7-embedded BOH+ and the reaction had the partial order of 1 with respect to alkali and hydroxide ions alike. LiOH induced the proton loss of the BOH+-CB7 complex much more efficiently than NaOH or KOH. These unexpected findings highlight the active role of alkali cations in the control of the kinetics of pH-responsive guest release from CB7 and provide a new way for the tuning of the temporal behavior of base-induced transformations of host–guest complexes.

Iron-triggered exsolution of FeNi alloy nanoparticles via topotactic cation exchange on Pr0.7Sr0.3Cr0.9Ni0.1O3−δ perovskite for CO2 electrolysis

Perovskites with in situ exsolved metal nanoparticles have been extensively studied for CO2 electrolysis in solid oxide electrolysis cell. However, exsolution process is strongly governed by the sluggish diffusion rate of cations and poor structural stability issues. Here we present a new exsolution process on redox stable Pr0.7Sr0.3Cr0.9Ni0.1O3−δ (PSCN) perovskite by topotactic exsolution. This process tends to generate host stoichiometric Pr0.7Sr0.3Cr0.9(FeNi)0.1O3−δ perovskite, triggering Ni cations segregation from the host while maintaining structural stability via supplement of Fe guest cations. The FeNi alloy nanoparticles decorated cathode showed a current density of 1.49 A cm−2 at 800 °C and 1.6 V for CO2 electrolysis, demonstrating over 62.0 % improvement compared to the primitive PSCN cathode. Experimental studies and density functional theory calculations revealed that the activity originated from the unique ability to adsorb and activate CO2 at the metal/perovskite interfaces. This cation supplement strategy may expand the frontiers in the evolution of exsolution on perovskite catalysts for CO2 utilization and other heterogeneous catalytic reactions.

Supramolecular Chemistry of Windmill-like Al10 Clusters: Adjustable Guests and Hydrogen-Bonding Networks for Enhanced Optical Limiting.

The interest in cluster chemistry lies not only in the development of new types of geometric structures but also in the higher-level connectivity and assembly of clusters at the supramolecular level. Here, we report a novel windmill-like Al10 cluster and consider this geometrically unique cluster as an anionic node assembled together with different cationic guests such as imidazolium and guanidinium. These guests with different hydrogen-bond angles can help to obtain a series of diverse hydrogen-bonding networks and then manipulate the stacking mode of hosts and guests. Furthermore, we realized a supramolecular approach to fine-tune the optical limiting properties of the cluster. This work not only enriches the host-guest chemistry of ionic windmill-like clusters but also opens up more possibilities for aluminum oxo cluster-based hydrogen-bonded frameworks.

Composition-Dependent Optical Properties of Cu–Zn–In–Se Colloidal Nanocrystals Synthesized via Cation Exchange

Copper chalcogenide-based nanocrystals (NCs) are a suitable replacement for toxic Cd/Pb chalcogenide-based NCs in a wide range of applications including photovoltaics, optoelectronics, and biological imaging. However, despite rigorous research, direct synthesis approaches of this class of compounds suffer from inhomogeneous size, shape, and composition of the NC ensembles, which is reflected in their broad photoluminescence (PL) bandwidths. A partial cation exchange (CE) strategy, wherein host cations in the initial binary copper chalcogenide are replaced by incoming cations to form ternary/quaternary multicomponent NCs, has been proven to be instrumental in achieving better size, shape, and composition control to this class of nanomaterials. Additionally, adopting synthetic strategies which help to eliminate inhomogeneities in the NC ensembles can lead to narrower PL bandwidths, as was shown by single-particle studies on I–III–VI2-based semiconductor NCs. In this work, we formulate a two-step colloidal synthesis of Cu–Zn–In–Se (CZISe) NCs via a partial CE pathway. The first step is the synthesis of Cu2–xSe NCs, which serve as a template for the subsequent CE reaction. The second step is the incorporation of the In3+ and Zn2+ guest cations into the synthesized Cu2–xSe NCs via simultaneous injection of both metal precursors, which results in gradient-alloyed CZISe NCs with a Zn-rich surface. The as-synthesized NCs exhibit near-infrared (NIR) PL without an additional shell growth, which is typically required in most of the developed protocols. The photoluminescence quantum yield (PLQY) of these Cu chalcogenide-based NCs reaches 20%. These NCs also exhibit intriguingly narrow PL bands, which challenges the notion of broad PL bands being an inherent property of this class of NCs. Additionally, a variation in the feed ratios of the incoming cations, i.e., In/Zn, results in the variation of the composition of the synthesized NCs. Henceforth, the optical properties of these NCs could be tuned by a simple variation of the composition of the NCs achieved by varying the feed ratios of the incoming cations. Within a narrow size distribution, the PL maxima range from 980 to 1060 nm, depending on the composition of the NCs. Post-synthetic surface modification of the synthesized NCs enabled the replacement of the parent long-chain organic ligands with smaller species, which is essential for their prospective applications requiring efficient charge transport. With PL emission extended into the NIR, the synthesized NCs are suitable for an array of potential applications, most importantly in the area of solar energy harvesting and bioimaging. The large Stokes shift inherent to these materials, their absorption in the solar range, and their NIR PL within the biological window make them suitable candidates.

Inside Cover: Supramolecular Enhancement of Charge Transport through Pillar[5]arene‐Based Self‐Assembled Monolayers (Angew. Chem. Int. Ed. 19/2023)

Non-covalent interaction modulation is a promising strategy to guide the design of applicable (supra)molecular electronics. A rare investigation of the relationship between host-guest interaction and supramolecular charge transport is reported by Xiaobing Li, Siyuan Zhou, Cunlan Guo, Shigui Chen, and co-workers in their Research Article (<url href=“https://doi.org/10.1002/anie.202216987”>e202216987). The current density through the pillar[5]arenes-based self-assembled monolayers can be raised up to ∼2.1 orders of magnitude after the introduction of cationic guest molecules, providing a new route for the design of molecular electronic devices and functional sensors with tunable electronic components.

Stimuli-Responsive Cucurbit[n]uril-Based Supramolecular Nanocarriers for Delivery of Chemotherapeutics

Chemotherapeutics commonly exhibit low bioavailability and systemic adverse effects. Supramolecular nanovesicles, such as pillar[n]arenes, calix[n]arenes, cucurbit[n]urils (CBs), and cyclodextrins, have been introduced as promising nanocarriers due to their remarkable encapsulation capacity and ability to host hydro-philic/-phobic guest molecules. Additionally, such nanovesicles can be decorated with various stimuli-responsive entities to enable drug targeting and controlled drug release. Self-assembly of amphiphilic cavitands and host–guest complexation represent the two common approaches for preparation of supramolecular nanovesicles with customizable surfaces capable of accommodating different biologically active guest molecules. CBs have been used as smart and multifunctional host macromolecules in cancer therapy. CBs are fabricated via a condensation reaction between formaldehyde and glycoluril units generating barrel-shaped supramolecules with partially enclosed cavities. The unique structure of CBs surrounding an internal hydrophobic cavity allows them to accommodate cationic and neutral guest molecules via ion-dipole and hydrophobic interactions, respectively. Additionally, CBs are stable, safe, and biocompatible, and their surfaces can be decorated with various functional targeting moieties. These advantages have promoted CBs as promising candidates for stimuli-responsive targeted delivery of chemotherapeutics. This review presents the most recent advances in the design of stimuli-responsive nanosystems based on CBs for effective cancer treatment.