Crown Ether Research Articles

Tailored Supramolecular Interactions in Host-Guest Complexation for Efficient and Stable Perovskite Solar Cells and Modules.

Host-guest complexation offers a promising approach for mitigating surface defects in perovskite solar cells (PSCs). Crown ethers are the most widely used macrocyclic hosts for complexing perovskite surfaces, yet their supramolecular interactions and functional implications require further understanding. Here we show that the dipole moment of crown ethers serves as an indicator of supramolecular interactions with both perovskites and precursor salts. A larger dipole moment, achieved through the substitution of heteroatoms, correlates with enhanced coordination with lead cations. Perovskite films incorporating aza-crown ethers as additives exhibited improved morphology, reduced defect densities, and better energy-level alignment compared to those using native crown ethers. We report power-conversion efficiencies (PCEs) exceeding 25 % for PSCs, which show enhanced long-term stability, and a record PCE of 21.5 % for host-guest complexation-based perovskite solar modules with an active area of 14.0 cm2.

Effect of crown ethers and polyglycols on the catalytic oxidation of cyclohexane and alkylarenes

Effect of crown ethers and polyglycols on the catalytic oxidation of cyclohexane and alkylarenes

Study of complexation of Li, Na and K trichloroacetates in extraction systems with benzo-15-crown-5 ether and its lipophilic analog

The extraction of Li, Na and K trichloroacetates by benzo-15-crown-5 ether and its lipophilic analog in chloroform has been studied. Extraction isotherms were obtained and the transition of extractants into the equilibrium aqueous phase was determined. The metal: crown ether ratios in the extracted compounds were determined by the slope analysis method. The thermodynamic extraction parameters of Li, Na and K trichloroacetates in systems with benzo-15-crown-5 ether (B15C5) and 3-tert-pentylbenzo-15-crown-5 ether (tPB15C5) were determined. The complexes [Li3(B15C5)(TCA)3], [Na(B15C5)(TCA)] and [K(B15C5)2](DCA)·H2O were isolated in crystalline form and characterized by IR spectroscopy and X-ray diffraction.

A mixed solvent system of amino crown ether and ionic liquids for a high-efficient extraction of cesium

Efficient extraction of Cs+ from aqueous solution was investigated by liquid–liquid extraction based on ionic liquids (ILs). In this study, Di(aminobenzo)-18-crown-6 (DAB18C6) was used as the extractant and three ILs (1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]), and 1-butyl-3-methylimidazolium bis-trifluoromethyl sulfonamide ([C4mim][NTf2])) were employed as co-extractants in the construction of a liquid–liquid extraction system for efficient and selective extraction of Cs+ from aqueous solutions. It was demonstrated that the DAB18C6-[C4mim][NTf2] mixed solvent system at 0.12 mol/L DAB18C6, a mass ratio of ILs/CHCl3 of 1:4 and a volumetric ratio of O/A of 1:1 exhibited a high % extraction of Cs+ up to 99.94 %, with a higher selectivity for Cs+ relative to coexisting ions such as K+ (βCs/K = 1216.7) and Rb+ (βCs/Rb = 139.03). The high selectivity of the extraction system for Cs+ was attributed to the lower hydration binding energy of Cs+ (−366.51 kJ/mol) and the stronger interaction between DAB18C6 and Cs+, g(r) = 12.7. Further, the hydrogen bonding interaction between the amino crown ether and ionic liquid increases the viscosity and surface tension of the extraction system, thus enhancing the stability of the system. Noteworthy, the most stable structure formed by DAB18C6-Cs+-[NTF2]− is attributed to cation exchange. In summary, this study demonstrates the great potential for efficient separation and extraction of cesium from aqueous solutions.

Janus Reactivity of Crownphyrinoids: Alkali- vs. Transition Metal-Mediated Transformations of Crown Ether-Porphyrin Hybrids.

Crownphyrinogens and crownphyrins constitute a group of macrocycles that combine the structural facets of porphyrinoids and crown ethers. The dual-nature cavity embedded in their molecules enables reactivity involving two structurally distinct parts of the macrocyclic ligand. Upon Ni(II) and Pd(II) insertion, coordination compounds are produced wherein the metal is incorporated into the porphyrinoid-like pocket, resulting in monomeric or accordion-like dimeric products, depending on the oxidation level of the macrocycle and metal cation. The reactions with Na(I) and K(I) resulted in the formation of complexes where only the crown ether segment of the molecule is involved in metal binding, yielding remarkable dimeric species. The exploitation of a crownphyrin large enough to accommodate two metal cations allowed the synthesis of an alkali/transition metal binuclear complexes wherein the macrocycle demonstrated the Janus reactivity with one cavity acting as a porphyrinoid, and the other mimicking the crown ether.

Facile synthesis of a new chiral polyimine macrocycle and its application for enantioseparation in high-performance liquid chromatography

Macrocyclic compounds such as crown ethers and cyclodextrins play an important role in the field of chromatography and show excellent separation performance. The design of simple and convenient methods for the efficient synthesis of novel chiral macrocycles for chromatographic separation is of great significance. In this work, a novel chiral polyimine macrocycle (PIMC) was designed and synthesized by the simply one-step reaction of 2,6-diformyl-4-tert-butylphenol with (S)-(-)-1,2-propanediamine. Then, it was bonded onto silica by the thiol-ene click reaction to construct a new chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC). The chiral separation performance of the proposed CSP was examined by separating various racemates in the normal-phase (NP) and reversed-phase (RP) HPLC. In total, twelve and nine racemates, including ethers, esters, amines, alcohols, organic acids, ketones, and epoxides, were separated to varying degrees via NP-HPLC and RP-HPLC, respectively, Moreover, the CSP offered good chiral separation complementarity to Chiralcel OD-H and Chiralpak AD-H columns for resolution of these test racemates, and it can separate several racemic compounds that either cannot be separated or cannot be separated well be separated by the two commercially available columns. After the column was used for hundreds of injections, the relative standard deviations of the retention time and resolution were below 0.56 % and 0.45 %, respectively, showing the good reproducibility and stability of the CSP. This study provides a simple and convenient approach to synthesize a novel chiral macrocycle and CSP and also indicates the broad application prospects of such chiral PIMCs in HPLC chiral separation.

Ultraselective Macrocycle Membranes for Pharmaceutical Ingredients Separation in Organic Solvents

Separations are core processes in the chemical and pharmaceutical industries. Several steps of fractionation and purification of multicomponent mixtures are required. Membrane technology can operate at fair temperatures, saving energy and processing sensitive compounds. However, breakthroughs require high stability and selectivity beyond those available today. Here, we propose membranes constituted by fully crosslinked crown ethers using interfacial polymerization. The 24 nm-thick nanofilms on robust porous supports exhibit up to 90% higher selectivity than commercially available membranes, with a 90% increase in solvent permeance. The membranes are tested with a complex mixture of structurally diverse solutes containing active pharmaceutical ingredients. The membranes are effective for the total retention and concentration of active pharmaceutical ingredients with molecular weights around 800 g mol–1. The ability to distinguish between smaller molecules in the range between 100 and 370 g mol–1 is confirmed with high separation factors, which could provide a significant advance for the pharmaceutical industry.

TPE-embedded butterfly bis-crown ether with controllable conformation and supramolecular chiroptical property

Understanding how subtle structural differences between macrocyclic conformational isomers impact their properties and separation has garnered increasing attention in the field of supramolecular synthetic chemistry. In this work, a series of tetraphenylene (TPE)-embedded butterfly bis-crown ether macrocycles (BCE[n], n = 4–7), comprising two crown ether side rings and a TPE core, are synthesized through intramolecular McMurry coupling. Unexpectedly, the presence of flexible oligoethylene chains with varying lengths are found to influence molecular conformation via multiple intramolecular interactions, resulting in the formation of two stabilized conformers with specific semi-rigid symmetric/asymmetric structures (sym-BCE[n] and asym-BCE[n], n = 5, 6). Moreover, it is noteworthy that neither symmetric nor asymmetric conformers are present in the more rigid BCE[4] or the more flexible BCE[7]. Interestingly, these conformers display distinct fluorescence properties and host-guest binding abilities, and only sym-BCE[5] can serve as a host for chiral polymer binding, resulting in the formation of chiral supramolecular assemblies through host-guest interaction induced chirality. Moreover, both circular dichroism and circularly polarized luminescence signals of the obtained assemblies can be switched off by the addition of sodium ion, suggesting potential applications in the field of dynamic chiral materials.

Crown ether dopant to reduce ion suppression and improve detection in the liquid microjunction surface sampling probe.

Sodium and potassium are required in agar media for the growth of some microorganisms (e.g., marine bacteria). However, alkali cations are a significant source of contamination for mass spectrometry causing ion suppression and adduct formation. Conventionally, salts can be removed before mass spectrometric analysis with appropriate and often lengthy sample preparation. The direct mass spectrometric sampling of bacterial colonies grown on agar media seeks to minimize or eliminate sample preparation to improve workflow. However, this may exacerbate ion suppression and contamination since these metal cations will degrade spectral quality and limit the rapid profiling of microbial metabolites. Different approaches are needed to sequester sodium and potassium ions to minimize unwanted background interferences. Herein, we use crown ethers (CEs) in combination with a liquid microjunction surface sampling probe (LMJ-SSP) to directly sample the surface of the bacterial colonies from two marine bacteria species (Pseudoalteromonas rubra DSM6842 and Pseudoalteromonas tunicata DSM 14096). CEs (e.g., 18-crown-6 or 15-crown-5) are added to the carrier solvent of the LMJ-SSP, the chemical noise is reduced, and spectra are easier to interpret. The liquid microjunction formed at the tip of LMJ-SSP was used to directly touch bacterial colonies on agar. The carrier solvent was either methanol (100%) or methanol: H2O (50:49.9%) with or without 0.01% CEs. Information-theoretic measures are employed to investigate qualitative changes between spectra before and after adding CEs. Our work demonstrates the capability of CEs to reduce background interferences within the direct profiling of bacterial colonies from agar plates. The data obtained from both P. rubra DSM6842 and P. tunicata DSM 14096 show that CEs can be used to mitigate the salty background and improve compound detection. Our approach can be implemented in natural product discovery using LMJ-SSP to allow fast and accurate detection of interesting/novel compounds.

Bioinspired Microgel-Loaded Smart Membrane Filtration with the Thermo- and Ion-Dual Responsive Water Gate for Selective Lead(II) Separation.

Lead (Pb2+) is a ubiquitous pollutant. Membrane filtration represents one of the most common water treatment methods, but nanofiltration and ultrafiltration require high transmembrane pressure, while microfiltration has larger pore sizes than ions, making them unfavorable for direct ion removal at low cost. Selective and direct separation of Pb2+ via membrane filtration at high efficiency without sacrificing the flux of clean water still remains challenging. Herein, inspired by the Pb2+-tolerable oleander that enriches and prevents Pb2+ in roots from permeating the plant body, a smart Pb2+-adsorptive filtration membrane with a temperature- and ion-tunable water gate was prepared by loading dual-responsive poly(N-isopropylacrylamido-co-acrylamido-benzo-18-crown-6) (PNB-5-20) microgels onto a commercial membrane. The PNB-5-20 microgel exhibits pronounced temperature-responsive swelling/deswelling (hydrodynamic diameter, 650-330 nm) with a volume phase transition temperature (VPTT) at ∼33 °C. Moreover, the microgel shows a high Pb2+-adsorption capacity (qmax, 85.4 mg/g) and good selectivity (distribution coefficient Kd ∼ 1000 mL/g) thanks to its complexation with the crown ether, as well as good Pb2+ responsiveness, having the VPTT positively shifted to 40 °C in the presence of Pb2+ with enhanced swelling behaviors. Functionalized with PNB-5-20, the smart membrane integrates Pb2+ detection, adsorption, and tunable water drainage in a single device. The membrane selectively recognizes Pb2+ in the polluted water with the gates in membrane pores switching from "open" to "closed", intercepting and adsorbing Pb2+ with water permeation reduced. Once purified, the gates can be "re-opened" by increasing the temperature. Construction of such an intelligent membrane filtration device with a tunable water gate and excellent Pb2+ recognition and adsorption performance will greatly simplify the remediation of Pb2+-polluted water.

Ultra-sensitive detection of cadmium and lead in water using crown ether gel electromembrane extraction coupled with miniaturized electrochemical system

This study presents the development of an electrochemical technique combined with gel electromembrane extraction (G-EME) for the simultaneous detection of cadmium and lead in environmental water samples. Crown ether (18C6) was added to the gel as a complexing agent and cationic carrier. The electrochemical responses were evaluated using differential pulse anodic stripping voltammetry (DPASV) across various pH levels and deposition times. The most sensitive response (acetate buffer pH 4, deposition time 90 s) was selected for the development of the G-EME process. By applying a 30 V electrical potential across the gel membrane containing 1 % (w/v) of 18C6 for 10 min, positively charged Cd2+ and Pb2+ ions migrated from the donor phase (pH 5.0) through the 18C6@gel membrane (pH 5.0) into the acceptor phase (pH 5.0). This resulted in a linear range from 0.3 to 5 µg/L for Cd2+ and 0.5 to 5 µg/L for Pb2+, with detection limits of 0.10 µg/L and 0.19 µg/L, respectively— up to 120 times more sensitive than direct electrochemical measurements. Furthermore, the proposed technique maintained selectivity for cadmium and lead, despite the presence of other potential heavy metal ions in the environment.

Crystal structure of (1,4,7,10,13,16-hexa-oxa-cycloocta-decane-κ6 O)potassium-μ-oxalato-tri-phenylstannate(IV), the first reported 18-crown-6-stabilized potassium salt of tri-phenyl-oxalatostannate.

The title complex, (1,4,7,10,13,16-hexa-oxa-cyclo-octa-decane-1κ6 O)(μ-oxalato-1κ2 O 1,O 2:2κ2 O 1',O 2')triphenyl-2κ3 C-potassium(I)tin(IV), [KSn(C6H5)3(C2O4)(C12H24O6)] or K[18-Crown-6][(C6H5)3SnO4C2], was synthesized. The complex consists of a potassium cation coordinated to the six oxygen atoms of a crown ether mol-ecule and the two oxygen atoms of the oxalatotri-phenyl-stannate anion. It crystallizes in the monoclinic crystal system within the space group P21. The tin atom is coordinated by one chelating oxalate ligand and three phenyl groups, forming a cis-trigonal-bipyramidal geometry around the tin atom. The cations and anions form ion pairs, linked through carbonyl coordination to the potassium atoms. The crystal structure features C-H⋯O hydrogen bonds between the oxygen atoms of the oxalate group and the hydrogen atoms of the phenyl groups, resulting in an infinite chain structure extending along a-axis direction. The primary inter-chain inter-actions are van der Waals forces.

Macrocycle-Based Supramolecular Drug Delivery Systems: A Concise Review.

Efficient delivery of therapeutic agents to the lesion site or specific cells is an important way to achieve "toxicity reduction and efficacy enhancement". Macrocycles have always provided many novel ideas for drug or gene loading and delivery processes. Specifically, macrocycles represented by crown ethers, cyclodextrins, cucurbit[n]urils, calix[n]arenes, and pillar[n]arenes have unique properties, which are different cavity structures, good biocompatibility, and good stability. Benefited from these diverse properties, a variety of supramolecular drug delivery systems can be designed and constructed to effectively improve the physical and chemical properties of guest molecules as needed. This review provides an outlook on the current application status and main limitations of macrocycles in supramolecular drug delivery systems.

Photoinduced synthesis of polymer-coated covalent organic framework microspheres for highly efficient lithium recovery

The increasing demand for lithium-ion batteries has led to a surge in global lithium consumption, calling for efficient extraction and recovery methods. Adsorption-based lithium recovery has gained attention for its simplicity, selectivity, and low energy requirements. However, conventional adsorption materials for lithium-ion (Li+) suffer from low surface area and covered active sites, resulting in slow recovery and inefficient uptake. Herein, we present a facile photoinduced synthesis of crown ether (CE)-based polymer grafted covalent organic framework (COF) microspheres, termed COF-CE, as an efficient lithium adsorbent. The COF-CE hybrid material possesses abundant nanochannels and highly porous surfaces, enabling rapid ion diffusion and enhancing ion accessibility to functional groups with the exclusive selectivity imparted by the grafted CE polymer towards Li+ over other monovalent cations. Notably, COF-CE exhibits exceptional absorption capacity (7.4 mg/g), rapid adsorption rates (k2 = 0.137 g mg−1 min−1) and high selectivity towards Li+, outperforming existing adsorbents. Moreover, COF-CE demonstrates remarkable Li+ regeneration and recycling capabilities, achieving near-unity recovery of lithium during the desorption phase and retaining 97 % of its adsorption capacity after five cycles. These results highlight the potential of COF-CE as an advanced adsorbent for lithium recovery in various applications, including industrial wastewater treatment and environmental remediation efforts.

Crown Ethers with Different Cavity Diameters Inhibit Ion Migration and Passivate Defects toward Efficient and Stable Lead Halide Perovskite Solar Cells.

Organic-inorganic hybrid metal halide perovskite solar cells have been considered as one of the most promising next-generation photovoltaic technologies. Nevertheless, perovskite defects and Li+ ionic migration will seriously affect the power conversion efficiency and stability of the formal device. Herein, we designed two crown ether derivatives (PC12 and PC15) with different cavity diameters, which selectively bind to different metal cations. It is found that PC15 in perovskite precursor solution can actively regulate the nucleation and crystallization processes and passivate the uncoordinated Pb2+ ions, while PC12 at the interface between the perovskite layer and hole-transporting layer can effectively inhibit the migration of Li+ ions and reduce nonradiative recombination losses. Therefore, PC12 and PC15 can act as "lubricant" and defect passivators, as well as inhibitors of ion migration, when they are synergistically applied at the surface and bulk of perovskite layer. Consequently, the optimized device achieved a champion efficiency of 24.8% with significantly improved humidity, thermal, and light stability.

Regulation of Zn2+ Solvation Configuration in Aqueous Batteries via Selenium-Substituted Crown Ether Engineering.

The efficient utilization of the metallic Zn in rechargeable aqueous Zn-ion batteries (RAZBs) struggle to suffer from parasitic Zn dendrite formation, hydrogen evolution reactions as well as severe interfacial degradation at high areal capacity loadings. This study thus proposes to employ the modified crown ether as an aqueous electrolyte additive to regulate the Zn2+ desolvation kinetic and facilitates the horizontally oriented (002) deposition of Zn, extending the lifespan of both the symmetric cell and full cell models. Specifically, zincophilic cyano and hydrophobic selenium atoms are incorporated into the crown ether supramolecule to enhance Zn2+ coordination and desolvation capability. The addition of 4-cyanobenzo-21-crown-7-selenium at a low concentration of 0.5 wt.% effectively mitigates hydrogen evolution and Zn corrosion caused by water, promoting the oriented deposition of Zn2+. The Zn||V2O5 full cell prototype, assembled with the areal capacity loadings of 2 mAh cm-2 and N/P ratio of 2.95, exhibits negligible capacity fading at 2.0A g-1 for 300 cycles, highlighting the commercial feasibility of supramolecular macrocycles additive for practical RAZBs applications.

Supramolecular Complexation-Enhanced CO2 Chemisorption in Amine-Derived Sorbents.

A supramolecular complexation approach is developed to improve the CO2 chemisorption performance of solvent-lean amine sorbents. Operando spectroscopy techniques reveal the formation of carbamic acid in the presence of a crown ether. The reaction pathway is confirmed by theoretical simulation, in which the crown ether acts as a proton acceptor and shuttle to drive the formation and stabilization of carbamic acid. Improved CO2 capacity and diminished energy consumption in sorbent regeneration are achieved.

Fabrication of Azacrown Ether-Embedded Covalent Organic Frameworks for Enhanced Cathode Performance in Aqueous Ni-Zn Batteries.

Crown ethers (CEs), known for their exceptional host-guest complexation, offer potential as linkers in covalent organic frameworks (COFs) for enhanced performance in catalysis and host-guest binding. However, their highly flexible conformation and low symmetry limit the diversity of CE-derived COFs. Here, we introduce a novel C3-symmetrical azacrown ether (ACE) building block, tris(pyrido)[18]crown-6 (TPy18C6), for COF fabrication (ACE-COF-1 and ACE-COF-2) via reticular synthesis. This approach enables precise integration of CEs into COFs, enhancing Ni2+ ion immobilization while maintaining crystallinity. The resulting Ni2+-doped COFs (Ni@ACE-COF-1 and Ni@ACE-COF-2) exhibit high discharge capacity (up to 1.27 mAh ⋅ cm-2 at 8 mA ⋅ cm-2) and exceptional cycling stability (>1000 cycles) as cathode materials in aqueous alkaline nickel-zinc batteries. This study serves as an exemplar of the seamless integration of macrocyclic chemistry and reticular chemistry, laying the groundwork for extending the macrocyclic-synthon driven strategy to a diverse array of COF building blocks, ultimately yielding advanced materials tailored for specific applications.

Supramolecular Assembly of Cesium Copper Iodine Resulting in Rich Emission Properties

AbstractCrown ether‐assisted supramolecular assembly is a robust strategy for manipulating low‐dimensional metal halides. In this study, the supramolecular assembly of 0D‐Cs3Cu2I5 is presented. Upon the addition of 15‐crown‐5 (15C5) to Cs3Cu2I5, 15C5 immediately coordinates with Cs+ to form the cone‐shaped [(15C5)Cs]+. Simultaneously, one of the iodine atoms is removed from the [Cu2I5]3‐ cluster, resulting in the formation of a sub‐planar rhombic [Cu2I4]2− unit. This process leads to white emission, specifically [(15C5)Cs]2[Cu2I4], which exhibits a photoluminescence quantum yield (PLQY) close to unity. The [(15C5)Cs]+ further reacts with 15C5 to form the sandwich‐type cationic structure [(15C5)2Cs]+, accompanied by the generation of red emission [(15C5)2Cs]2[Cu2I4]. By carefully controlling the amount of 15C5, various emission composites can be achieved, particularly tunable white emission. The assembly process is reversible. The pristine Cs3Cu2I5 can be recovered after thermal curing because of the volatility of crown ether and the weak Cs‐crown ether bond. Theoretical calculations have demonstrated that the coordination of the crown ether primarily affects the energy level, leading to changes in the excited state and photophysical properties. The applications in anticounterfeiting and LED phosphors have been demonstrated. This work provides a new approach for the development of low‐dimensional copper halides with promising applications in optoelectronics.

A Matthew MXene (Ti3C2Tx) Lamellar Membrane as a Potassium-Sieving Amplifier

Transport channels with ultrahigh K+ selectivity over other ions play a crucial role for living beings, but constructing ionic channels with promising K+ selectivity and permeability remains a challenge. Here, an asymmetric bilayer membrane based on MXene (Ti3C2Tx) lamellar channels consisting of a recognition layer (RL) on top of an enhancement layer (EL) exhibits an amazing Matthew effect: amplification of the preferred transport of K+, resulting in an excellent K+-separation performance. The K+ ion is selected by the 1-aza-18-crown-6 ether-modified RL, owing to preferential affinity energy, and then rapidly transported as a hydrated ion through the EL, based on the confinement effect. Other undesired ions such as Na+ are hindered from entering the RL by the preferred K+ occupation of the crown ether. The MXene (Ti3C2Tx)-based Matthew membrane presents high K+-permeation rates of 0.1–0.2 mol∙m–2∙h–1, with a significant K+/Na+ selectivity of 5–9. The molecular separation mechanism of the Matthew membrane is investigated deeply to explore the nature of the Matthew amplification effect on K+ sieving, where the precise matching of the RL and EL within the membrane governs the fast K+ permeation with good selectivity. The asymmetric structure of our Matthew membrane is the key to understanding the biological function of ion channels for precise and fast ion transport, which will guide us in the creation of artificial ion channels or membranes.