Functionalized Crown Ethers Research Articles

Molecular insight into the separation mechanism of crown Ether-Based channels for lithium Extraction

The shortage of lithium resources can be effectively improved by using membrane separation technology to extract lithium from salt lake brines that contain rich Li. In this study, GO modified with functionalized crown ether group (2)-hydroxymethyl-15-crown-5,15C) was used as a separation membrane for Li+/Mg2+. The effect of 15C and its content on the separation mechanism of Li+/Mg2+ in membrane was designed and studied by molecular dynamics simulation. Improving water permeability of the membrane can be achieved with the appropriate amount of 15Cs, but an excessive amount of 15C will result in channel obstruction, which is not conducive to the transport of water molecules. In addition, the special recognition of Li+ by 15Cs enhances the transmission of Li+ within the channel. Finally, it is found that the dehydration behavior of Li+ is facilitated by the interaction between 15Cs and Li+. As the diameter of Li+ is smaller than the diameter of the 15C cavity, dehydrated Li+ passes through the 15C cavity with ease under pressure. This means that during the separation process, Li+ enters a “dual transport” mode. The membrane gains higher permeability for Li+ while blocking Mg2+. This study clarifies the rapid transport mechanism of Li+ in GO-15C，which provides a feasible strategy for designing highly selective Li+/Mg2+ separation membranes.

Selective Separation of Lithium Chloride by Organogels Containing Strapped Calix[4]pyrroles

Reported herein are two functionalized crown ether strapped calix[4]pyrroles, H1 and H2. As inferred from competitive salt binding experiments carried out in nitrobenzene-d5 and acetonitrile-d3, these hosts capture LiCl selectively over four other test salts, viz. NaCl, KCl, MgCl2, and CaCl2. Support for the selectivity came from density functional theory (DFT) calculations carried out in a solvent continuum. These theoretical analyses revealed a higher innate affinity for LiCl in the case of H1, but a greater selectivity relative to NaCl in the case of H2, recapitulating that observed experimentally. Receptors H1 and H2 were outfitted with methacrylate handles and subject to copolymerization with acrylate monomers and cross-linkers to yield gels, G1 and G2, respectively. These two gels were found to adsorb lithium chloride preferentially from an acetonitrile solution containing a mixture of LiCl, NaCl, KCl, MgCl2, and CaCl2 and then release the lithium chloride in methanol. The gels could then be recycled for reuse in the selective adsorption of LiCl. As such, the present study highlights the use of solvent polarity switching to drive separations with potential applications in lithium purification and recycling.

Crown ether-based anion exchange membranes with highly efficient dual ion conducting pathways

Anion exchange membranes (AEMs) are a crucial constituent for alkaline fuel cells. As the core component of fuel cells, the low performance AEMs restrict the development and application of the fuel cells. Herein, the trade-off between the OH– conductivity and dimensional stability was solved by constructing AEMs with adequate OH– conductivity and satisfactory alkali resistance using Tröger’s base (TB) poly (crown ether)s (PCEs) as the main chain, the embedded quaternary ammonium (QA) and Na+-functionalized crown ether units as the cationic group. Crown ether is an electron donator, and can capture Na+ to form Na+-functionalized crown ether units to conveniently transfer OH– and significantly promote the alkaline stability of the AEMs. The influence of the Na+-functionalized crown ether units on the performance of AEMs was studied in detail. The PCEs based AEMs show an obvious hydrophobic-hydrophilic microphase separation. These features make them ideal platforms for the OH– conduction applications. As expected, the as-prepared PCEs-QA-100% (100% is the degree of cross-linking) AEM with an ionic exchange capacity (IEC) of 2.07 meq g−1 has a high OH– conductivity of 159 mS cm−1 at 80 °C. Furthermore, the membrane electrode assemblies fabricated using the PCEs-QA-100% AEM possess a maximum power density of 291 mW cm−2 under the current density of 500 mA cm−2.

Novel polymer crafted sugar thiacrown ether and its applications in recovery of metal ions

Polymeric macrocycles are important as complexation agents in chemistry. The multivalent binding of heteroatoms inside the macrocycle to metals and organic pollutants has gained much interest. A protecting group strategy was applied to synthesise functionalized crown ether based on glucose. The 4,6-position was protected by benzylidene, and arms were introduced on the remaining hydroxyls in 2- and 3-positions. Cyclization was achieved through sodium sulfide in ethanol. The selective cleavage of the benzylidene protecting group left the free hydroxyl group on C-6 position. The propargyl group was introduced and attached the macrocycles to polyvinyl azide by click reaction. The compounds were identified by nuclear magnetic resonance, infrared spectroscopy and mass spectrometry, and the morphology and thermal stability of the polymer were characterized via field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray powder diffraction and differential scanning calorimetry. The removal of metal ions Co, Cd and Pb was performed by atomic absorption spectrometry in different experimental conditions. The results indicated that synthesised crown ether can effectively removal such metals and has highly sufficient recyclability.

Preparation and Spectroscopic Characterization of Iron(III) Complexes of a Functionalized Crown Ether

Preparation and Spectroscopic Characterization of Iron(III) Complexes of a Functionalized Crown Ether

Synthesis and applications of (5-substituted benzimidazolo)-benzo-15-crown-5 and 4,4′-bis-benzimidazolo-dibenzo-15-crown-5 for the colorimetric detection of Au3+

AbSTRACTIn the present work, we have reported the synthesis of benzimidazoles functionalized crown ether derivatives of 4-formyl benzo-15-crown-5/4,4′-diformyl dibenzo-15-crown-5 and substituted diamine pyridine using sulfamic acid as a catalyst in DMSO. These molecules are used for the colorimetric determination of Au3+ selectively among other metal cations such as Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Pb2+, Hg2+, Au3+ and Ag+ ions.

Exploring crown-ether functionalization on the stabilization of hexavalent neptunium.

Crown-ether molecules are used in radiochemical separations due to their high selectivity for a range of metal cations. Previous investigations regarding the interactions of 18-crown-6 (18C6) with 237Np suggested the formation of a Np(v) inclusion complex, but also reported rapid reduction of Np(vi) to Np(v) in the presence of the ether molecule. Herein, we investigate the impact of crown ether functionalization by exploring the Np(v) and Np(vi) dicyclohexano-18-crown-6 (DCH-18C6) systems. Two [X(DCH-18C6)]2[Np(vi)O2Cl4] compounds (X = K (1) and Na (2)) were crystallized and characterized by single crystal X-ray diffraction and Raman spectroscopy. Additional studies of Np(vi), Np(v), and Np(v)/Np(vi) in solution indicated redox stability in the presence of functionalized crowns and preferential crystallization of Np(vi) DCH-18C6 solids. These results indicate that functionalization of the crown can lead to higher resistance to radiolysis and increased stability of the Np(vi) oxidation state in solution.

Desymmetrization of disubstituted aromatic crown ethersviaintramolecular Cannizzaro reactions

Ba++templated Cannizzaro reactions convert symmetrical aromatic crown ether dialdehydes of various types [dibenzo and bis(meta-phenylene)] and sizes (20–32 atom rings) to acid–alcohol functionalized crown ethers in 70–98% yields.

Structure, Dynamics, and Adsorption of Charged Guest within the Nanocavity of Polymer-Functionalized Neutral Macrocyclic Host.

Host-guest encapsulation has been widely applied for purification and seizing of the metal ions. Macrocyclic crown ethers are one of the most popular hosts in the field of host-guest chemistry, which on functionalization with polymers are employed as an effective adsorbent. In spite of their vast applications, the microscopic information about their sensing mechanism toward cations/molecules is very scarce. Therefore, the present study is focused on the molecular insights of ion-exchange mechanism within the cavity of crown ether-functionalized polymers using molecular dynamics (MD) simulations. This present study investigates the molecular-level events of chloromethylated polystyrene (CMPS) bearing dibenzo-18-crown-6 (DB18C6) in the aqueous and acidic environment, which has been found to be particularly successful in sensing of various alkali and alkali earth metal ions. A strategy has been envisaged to design a crown ether-based functionalized polymeric resin, which exhibits good match of properties with the in-house-synthesized resin. The MD studies well capture the experimentally observed Langmuir-type adsorption isotherms of Li+ ions on crown ether-grafted polymer resins. The presence of acid reduces the adsorption of Li+ ions due to the competition with H3O+ ions. In addition, the results revealed that the "adsorption in crown cavity" follows a dual residence time function. To the best of our knowledge, this is the first report on the adsorption isotherm of functionalized crown ether using MD simulations. The structure and dynamics of binding sites were explored using radial distribution functions and diffusion coefficients. All of these effects have been studied for different Li+-ion concentrations, acid concentrations, and counterions as well as different lengths of polymer chains and degrees of polymerization. Overall, the present study provides insights into and quantitative information about adsorption on the CMPS-DB18C6 resin, which might be useful in myriads of host-guest-based adsorption experiments.

Molecular engineering of functionalized crown ether resins for the isotopic enrichment of gadolinium: from computer to column chromatography

Computer aided molecular engineering of functionalized crown ethers for isotope separation of gadolinium using column chromatography.

Clustomesogens: Liquid Crystalline Hybrid Nanomaterials Containing Functional Metal Nanoclusters.

Inorganic phosphorescent octahedral metal nanoclusters fill the gap between metal complexes and nanoparticles. They are finite groups of metal atoms linked by metal-metal bonds, with an exact composition and structure at the nanometer scale. As their phosphorescence internal quantum efficiency can approach 100%, they represent a very attractive class of molecular building blocks to design hybrid nanomaterials dedicated to light energy conversion, optoelectronic, display, lighting, or theragnostic applications. They are obtained as AnM6X(i)8X(a)6 ternary salt powders (A = alkali cation, M = Mo, Re, W, X(i): halogen inner ligand, X(a) = halogen apical ligand) by high temperature solid state synthesis (750-1200 °C). However, their ceramic-like behavior has largely restricted their use as functional components in the past. Since these last two decades, several groups, including ours, started to tackle the challenge of integrating them in easy-to-process materials. Within this context, we have extensively explored the nanocluster ternary salt specificities to develop a new class of self-organized hybrid organic-inorganic nanomaterials known as clustomesogens. These materials, combine the specific properties of nanoclusters (magnetic, electronic, luminescence) with the anisotropy-related properties of liquid crystals (LCs). This Account covers the research and development of clustomesogens starting from the design concepts and synthesis to their introduction in functional devices. We developed three strategies to build such hybrid super- or supramolecules. In the covalent approach, we capitalized on the apical ligand-metal bond iono-covalent character to graft tailor-made organic LC promoters on the {M6X(i)8}(n+) nanocluster cores. The supramolecular approach relies on the host-guest complexation of the ternary cluster salt alkali cations with functional crown ether macrocycles. We showed that the hybrid LC behavior depends on the macrocycles structural features. Finally, a third strategy, known as the ionic-assembling strategy, exploits the anionic character of the [M6L14](n-) nanocluster units whose charge is counterbalanced by tailor-made organic cations. We first focused on rationalizing the structural-LC behavior relationships of these noncovalent nanostructured materials by using NMR, SAXS, DSC, and POM technics. Depending on the hybrid organic-inorganic volumic fraction, thermotropic layered or nematic phases were observed. In this last case, the nematic phase being the most fluid of all LC phases, we further investigated this class of clustomesogen by introducing them in electro-controlled devices to tune either their photoluminescence or observe polarized emission. We hope this Account will provide useful tools for the development of new materials integrating such bright but still underused inorganic phosphors.

Selective recognition and extraction of KBr via cooperative interactions with a urea functionalized crown ether dual-host.

Selective solid-liquid extraction of KBr is demonstrated for the first time with a crown ether based pentafluorophenyl urea functionalized dual-host receptor. (1)H-NMR and ITC studies have been carried out to illustrate the effect of cooperativity towards the recognition of alkali metal salts.

Direct and indirect single electron transfer (SET)-photochemical approaches for the preparation of novel phthalimide and naphthalimide-based lariat-type crown ethers.

In this review, we describe direct and indirect photochemical approaches that have been developed for the preparation of phthalimide- and naphthalimide-based, lariat-type crown ethers. The direct route utilizes a strategy in which nitrogen-linked side chains containing polyethoxy-tethered phthalimides and naphthalimides, possessing terminal α-trialkylsilyl groups, are synthesized utilizing concise routes and UV-irradiation to form macrocyclic ring systems. In contrast, the indirect route developed for the synthesis of lariat-type crown ethers employs sequences in which SET-promoted macrocyclization reactions of α-trialkylsilyl-terminated, polyethoxy-tethered phthalimides and naphthalimides are followed by a side chain introduction through substitution reactions at the amidol centers in the macrocyclic ethers. The combined observations made in these investigations demonstrate the unique features of SET-promoted photocyclization reactions that make them well-suited for the use in the synthesis of functionalized crown ethers. In addition, while some limitations exist for the general use of SET-photochemical reactions in large-scale organic synthesis, important characteristics of the photoinduced macrocyclization reactions make them applicable to unique situations in which high temporal and spatial control is required.

Convenient Synthesis of Building-Blocks for Pyridine/Piperidine-Decorated Crown Ethers

A convenient way to 1-(pyridin-2-yl)ethan-1,2-diol, 2-(oxiran-2-yl)pyridine and two diastereomeric forms of 1-(piperidin-2-yl)ethan-1,2-diol, valuable building-blocks for the synthesis of functionalized crown ethers, has been developed. It is based on the Wagner oxidation or NBS-mediated epoxydation of 2-vinylpyridine, and the Schwenk-Papa reduction of 1-(pyridin-2-yl)ethan-1,2-diol, accompanied by fractional crystallization of a diastereo-meric mixture of the target product.

Influence of the ring size in diphosphorylated dibenzo crown ethers on extraction of metals from nitric acid solutions

Extraction of metals from 0.1–7 M HNO3 with 0.05 M chloroform solutions of functionalized crown ethers containing (n-C4H9O)2P(O)- fragments and differing in the polyether ring size (18-crown-6, 21-crown-7, 24-crown-8) was studied. An increase in the size of the macroring in diphosphorylated dibenzo crown ethers leads to an appreciable increase in the performance of the extractants toward a number of metals, due to participation of phosphoryl groups in the complexation. At the same time, the reactivity of the macroring varies insignificantly, which decreases the selectivity of the recovery of metals forming host-guest complexes. These features should be taken into account when designing new macrocyclic extractants of the lariat type.

Binding of a hemoregulatory tetrapeptide by a bis-guanidinium crown ether

A synthetic receptor for the molecular recognition of a tetrapeptide in aqueous buffer was obtained by combining a luminescent crown ether with two pyrrole-guanidinium moieties. The compound interacts with ammonium carboxylates of complementary geometry and binds the hemoregulatory peptide Ac-Ser-Asp-Lys-Pro with K=7×10 3 M −1 at physiological pH. Shorter fragments and other tetrapeptides show no or significant reduced affinity. The binding of the target peptide to the functionalized crown ether is signalled by an increase of its emission intensity.

ChemInform Abstract: Photoaddition of Aliphatic Ethers to 4-Methyl-1,2,4-triazoline-3,5-dione: Application to the Synthesis of Functionalized Crown Ethers and Mechanism.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Preparation and spectroscopic characterization of iron(II) and copper(II) complexes of a functionalized crown ether

Condensation between 4′-aminobenzo-15-crown-5- and 4-antipyrinecarboxaldehyde yielded the functionalized crown ether (L = 1,5-dimethyl-4-[(2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin-15-ylimino)methyl]-2-phenyl-1,2-dihydro-3H-pyrazol-3-one). A 1:1 (Na+:L) complex has been prepared. The reaction of Fe(II) and Cu(II) salts with L gave complexes of composition [Fe(L)Cl2] and [Cu(L)2Cl2]. Heteronuclear complexes [Fe(L)Cl2Na]ClO4 and [Cu(L)2Cl2Na]ClO4 have also been synthesized from the reactions of [Fe(L)Cl2] and [Cu(L)2Cl2] with NaClO4. The compounds have been characterized by microanalyses and spectroscopic methods.

ChemInform Abstract: Short and Efficient Synthesis of Thiol Group Functionalized Crown Ethers.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Short and Efficient Synthesis of Thiol Group Functionalized Crown Ethers

A synthesis of thiol group functionalized crown ethers is reported. The reaction is accomplished by the direct chlorosulfonation of simple crown ethers with chlorosulfonic acid and the reduction of the sulfonyl chloride moiety with LiAlH4 in two steps. This new process is simple to operate, and it generates high‐purity mercaptobenzocrowns with excellent yields.