Crown Ether Structure Research Articles

Study on the preparation and properties of lignin-based flexible polyurethane foams with NaCl as a medium.

Currently, most polyols used in polyurethane foam (PUF) synthesis are derived from petrochemicals. However, lignin as the most abundant aromatic biopolymer rich in hydroxyl groups, is a suitable filler for synthesizing polyurethane foam. Therefore, in this study, Kraft lignin (KL) was utilized as a partial substitute for flexible polyethylene glycol 400 (PEG400). After adding 15 % KL, NaCl was introduced as a medium for synthesizing LFPUF and Polydimethylsiloxane (PDMS) was used as a foam stabilizer. Lignin-based flexible polyurethane foam (LFPUF) with high elasticity was synthesized. The aromatic ring structure of KL acted as a reinforcement for the foam, while the flexible PEG400 provided excellent flexibility to LFPUF. Na+ interacts with oxygen atoms in the long chain of PEG to form a cyclic crown ether structure. This promotes proximity and ordering of the hydroxyl groups, thereby facilitating proton transfer and optimising the cell size of the foam. Ultimately, the foam synthesized with 3 % NaCl (LFPUF-3%NaCl) exhibited an average cell size and hole size of 484.1 and 183.6 μm, respectively, significantly smaller than those of the foam synthesized without NaCl (843.5 and 249.3 μm, respectively). The foam resilience and elastic recovery of LFPUF-3%NaCl were 39.56 and 99.03 %, respectively, which was higher than that of the foam synthesized without NaCl (20.36 % and 97.08 %, respectively). In addition, LFPUF-3%NaCl maintained a high elastic recovery of 97.61 % after 20 cycles of compression. The egg drop test demonstrated that the foam effectively provided protective cushioning for fragile items.

Conformational Selectivity and Chiral Self-Assembly Structures of Crown Ethers on Metal Surfaces.

Crown ethers (CEs), macrocyclic polyethers, have attracted significant attention in supramolecular chemistry. It is known that they have many isomers due to their flexibility. It is challenging to select some exact conformation and tune the following self-assembly structure of CEs, and it has rarely been reported to date. Herein, by choosing 18-crown-6-ether and dibenzo-18-crown-6-ether for study, we report an effective stereoisomeric selectivity of CEs by a strategy of both chemical modification and CEs hosting Na/K ions. The conformational difference in CEs can further tune the molecular interactions, resulting in the chiral self-assembly structures of CEs. By the combination of scanning tunneling microscopy, density functional theory, and X-ray photoelectron spectroscopy, this study reveals the underlying mechanism of CEs in both conformational selectivity and the formation of chiral assembly structures.

Solvent-free synthesis of covalent-framework 2D crown ether and its application for polylactic acid nanocomposites having antibacterial property

This study showed the synthesis of a covalent-frameworked 2D crown ether, named C2O, consisting of carbon and oxygen in a 2:1 mol ratio, using solvent-free synthesis for the first time. The synthesized C2O is distinguished by its structure, which includes numerous phenol groups akin to phlorotannins, conferring high antibacterial property through contact-based mechanisms and biocompatibility. The inherent crown ether structure of C2O facilitates efficient metal adsorption, allowing for the easy facile preparation of C2O containing Cu atom (Cu@C2O). Cu@C2O exhibits enhanced antibacterial property at much lower concentrations compared to the native C2O. For practical application, polylactic acid (PLA) nanocomposite films were prepared using C2O as a filler, achieving 99.99 % of antibacterial property at just 0.1 wt% concentration. When the PLA nanocomposite films were prepared using Cu@C2O as the filler, the required concentration was further reduced to 0.03 wt%, while still demonstrating 99.99 % of antibacterial property. Additionally, the excellent copper ion adsorption capacity of Cu@C2O ensures minimal leaching, thus mitigating cytotoxicity concerns. Given their high and long-term antibacterial properties, biocompatibility, these materials represent promising candidates for various biomedical, packaging and antifouling paint applications, demonstrating significant potential across diverse domains.

Reverse osmosis membrane with crown ethers decoration for enhanced radionuclides sieving

Reverse osmosis (RO) membranes have been widely applied in the increasingly discharged radioactive wastewater treatment. However, conventional RO membranes suffer from the issues of the limited nuclides rejections and the relatively low water permeance. In this work, a new type of RO membrane with decoration of crown ethers (15C5 and 18C6) was prepared via an interfacial polymerization process to remove the radionuclide-contaminated components. Due to the special hollow structure of crown ethers (CEs) and the hydrogen bonding within the amidogen, the obtained MPD@15C5-TMC and MPD@18C6-TMC membranes exhibited smoother surfaces and thinner polyamide active layers than the pristine MPD-TMC membrane. The optimized MPD@15C5-TMC and MPD@18C6-TMC RO membranes presented excellent pure water permeances up to 2.16 and 2.91 L m−2 h−1 bar−1, and maintained high rejections towards Cs+, Sr2+ and Co2+, respectively. Furthermore, the membrane possessed a remarkable operational stability and an excellent anti-fouling property. These results confirmed the possibility of adopting crown ethers for RO membrane fabrication and verified their great potential for the practical application in removing radioactive elements from wastewater.

Synthesis of crown-ether-embedded graphene by the solution plasma

Crown ethers consisting of several ether linkages (R–O–R′) have been attracting attention in the fields of inorganic and organic chemistry, attributed to their cavity sizes and superior cation selectivity. However, they exhibit comparatively low selectivity and ion-binding affinities due to their structural flexibility. Recent studies have shown that crown ethers rigidly formed within 2D matrices, e.g., graphene, exhibit enhanced binding energy and selectivity. However, most of these studies were based on computational modeling and simulations. In this study, the synthesis of crown-ether-embedded graphene was attempted for the first time by the solution plasma process (SPP). Crown-ether-embedded graphene was successfully synthesized through C–H activation and polymerization reactions between as-produced intermediates (i.e., polycyclic aromatic hydrocarbons, including multiply fused benzene rings) and activated cation radicals. Structural and chemical analyses were conducted to verify the existence of the crown ether structure (cyclic ether, C–O–C) in the carbon matrix, and a 2D graphene structure with a cavity originating from the crown ether was observed by transmission electron microscopy analysis. Moreover, adsorption test confirmed successful synthesis of crown ether-embedded graphene with ordered cavity size. We believe that the proposed synthesis approach for crown ether-embedded graphene will be valuable for a wide range of applications, such as ion-selective membrane applications and waste cleanup.

Supported ionic liquid membrane contactor with crown ether functionalized polyimide membrane for high-efficient Li+/Mg2+ selective separation

Worldwide demand for lithium is increasing rapidly. Implementing an efficient extraction for lithium from salt-lake brines with low concentration and high Mg/Li (m/m) ratio remains challenging. A supported ionic liquid membrane (PI@14C4-SILM) contactor was developed in this work using a crown ether functionalized polyimide membrane material (Poly(DAB14C4-6FDA)) as the support and tributyl phosphate (TBP) and (1-butyl-3-methylimidazolium bis-trifluoromethylsulfonimide salt) ([C4mim][NTf2]) mixture as the liquid phase for high-efficiency Li recovery. The results show that when the feed phase Mg/Li ratio is 35 and the stripping phase is 0.5 mol/L HCl, the Li+ penetration rate, initial flux and Li/Mg selectivity of PI@14C4-SILM contactor are 0.354 μm/s, 0.128 mol/m2·h and 19.1, respectively. Molecular dynamics (MD) simulation results show that Poly(DAB14C4-6FDA) and TBP have greater interaction with Li+ than other ions (Na, Mg, K). Meanwhile, the binding energies of Poly(DAB14C4-6FDA)-Li-NTf2 and TBP-Li-NTf2 were calculated by density functional theory (DFT), which were −163.26 and −182.1 kcal/mol, respectively. The higher binding energies of the complexes indicated that their structures were more stable. The mechanism of the PI@14C4-SILM contactor's excellent Li+ mass transfer performance may be the formation of a fast Li+ transfer channel between the solid phase containing the crown ether structure and the liquid mobile phase in the pore structure. Besides, the TBP·Li·NTf2 and TBP·H·NTf2 structures in the liquid membrane phase effectively maintained the cyclic operation of the SILM system. This study provides an effective solution for selective separation of Mg/Li and utilization of Li resources in salt lake water.

Extraction of cesium and strontium from nitric acid hlw by a mixture of extractants of -18-crown-6 and -21-crown-7 derivatives in organic solvents

The processes of extraction of stable isotopes of cesium and strontium by solutions of macrocyclic polyesters in organic solvents from nitric acid mediums have been studied. The e ect of the crown ether structure and solvent type on the distribution coe cients of cesium ( D Cs) and strontium ( D Sr) has been studied. Extraction systems for the combined extraction of cesium and strontium were tested, in which 1,1,7-trihydrododeca uoroh eptanol and chlorohydrocarbons were used as solvents. It is shown that the highest D Cs and D Sr in the combined extraction of metals are observed when using a mixture of DTBDB18C6 and DCH18C6. Experimental data con rm the high e ciency of the use of crown ethers for the extraction of cesium and strontium into a separate fraction when handling radioactive waste.

Synergistic Effect of Crown Ether and Main‐Chain Engineering for Boosting Hydrogen Evolution of Polymer Photocatalysts in Seawater

AbstractPhotocatalytic hydrogen evolution from natural seawater faces the severe challenges of abundant salts, which adsorb on the active sites and result in undesirable side reactions and photocatalyst poisoning. Herein, a series of main‐chain‐engineered discontinuously conjugated polymer (DCP) photocatalysts is presented with bifunctional crown ether (CE) structures for hydrogen evolution from seawater. The hydrophilic CE can significantly inhibit the aggregation of DCPs induced by salts. Meanwhile, cyclic CE can effectively adsorb cations to uncover the active sites to increase their interaction with protons, which can increase the hydrogen evolution rates and significantly reduce the efficiency roll‐off in natural seawater. Through atomistic studies, the formation of hydrogen bonds with bifunctional CE is elucidated and further analysis of the microscale mechanisms is also conducted using molecular dynamics and ab initio techniques. This work suggests that CE‐based polymer has the potential to enhance its ability to produce hydrogen through photocatalysis using seawater.

Structural engineering on 6FDA-Durene based polyimide membranes for highly selective gas separation

In this work, four diamine monomers, selected based-on steric hindrance and affinity with gas to be separated, were separately introduced into 6FDA-Durene to prepare co-polyimides. The influences of incorporating diamine monomer geometry on free volume elements (FFV, FAV, cavity size distribution, surface area and cavity connectivity) and gas transport properties (solubility and diffusion) of synthesized co-polyimide membranes were systematically investigated. The introduction of second amino monomer can increase gas selectivity, however leaded to lower gas permeability. Gas solubility and solubility selectivity of membrane remained almost stable with introduction of different amino monomer. While the gas diffusion changed remarkably, and the diffusion selectivity increased by about 170%. The FDDA membrane with crown ether structure displayed the highest gas selectivity (increased by 122%, 121%, 158%, 115% and 115% for H2/N2, H2/CH4, O2/N2, CO2/N2 and CO2/CH4, respectively, compared to 6FDA-Durene membrane), whose selectivity was relatively high among the PI-based membranes. This can be explained that the crown ether group granted the membrane with largest FAV ratio of specific gas pair, as well as the smallest pore size that would cause stronger size sieving effect. These results indicated that gas separation property of polyimide membranes can be effectively adjusted via tuning monomer structure, which is easily synthesized or has been commercialized, to realize the industrial application of membrane-based gas separation.

Cellulose-Based Hectocycle Nanopolymers: Synthesis, Molecular Docking and Adsorption of Difenoconazole from Aqueous Medium.

The goal of this work was to develop polymer-based heterocycle for water purification from toxic pesticides such as difenoconazole. The polymer chosen for this purpose was cellulose nanocrystalline (CNC); two cellulose based heterocycles were prepared by crosslinking with 2,6-pyridine dicarbonyl dichloride (Cell-X), and derivatizing with 2-furan carbonyl chloride (Cell-D). The synthesized cellulose-based heterocycles were characterized by SEM, proton NMR, TGA and FT-IR spectroscopy. To optimize adsorption conditions, the effect of various variable such as time, adsorbent dose, pH, temperature, and difenoconazole initial concentration were evaluated. Results showed that, the maximum difenoconazole removal percentage was about 94.7%, and 96.6% for Cell-X and Cell-D, respectively. Kinetic and thermodynamic studies on the adsorption process showed that the adsorption of difenoconazole by the two polymers is a pseudo-second order and follows the Langmuir isotherm model. The obtained values of ∆G ° and ∆H suggest that the adsorption process is spontaneous at room temperature. The results showed that Cell-X could be a promising adsorbent on a commercial scale for difenoconazole. The several adsorption sites present in Cell-X in addition to the semi crown ether structure explains the high efficiency it has for difenoconazole, and could be used for other toxic pesticides. Monte Carlo (MC) and Molecular Dynamic (MD) simulation were performed on a model of Cell-X and difenoconazole, and the results showed strong interaction.

Products and kinetics of the cationic ring-opening polymerization of 3-glycidoxypropylmethyldimethoxysilane by lithium perchlorate

The cationic ring-opening polymerization (ROP) of 3-glycidoxypropylmethyldimethoxysilane (GMDM) induced by anhydrous lithium perchlorate (LiClO4) was investigated along with the sol-gel reaction of the methoxy groups. The polymer constructed using poly(ethylene oxide) (PEO) prepared from the ROP of epoxy groups and a subsequent sol-gel reaction of the methoxy groups was found to be a free-standing and transparent solid. The polymer exhibited ionic conductivity explained by the Vogel–Tamman–Fulcher (VTF) equation. Study of the PEO polymerization process and analysis of the byproducts were performed. A study of the reaction kinetics estimated the activation energy of ROP to be 77.9 ± 2.0 kJ mol−1. In addition to the linear PEO structure, cyclic products with a crown ether structure were also produced. It was also determined that the ROP and sol-gel reactions of the methoxy groups proceeded independently. The color change obtained following the reaction was explained by considering the Rayleigh scattering of visible light from the nanoparticles constructed from the ring-opened polymerized products of the epoxy groups.

LCST phase behavior of benzo-21-crown-7 with different alkyl chains.

The introduction of hydrophobic units into crown ethers can dramatically decrease the critical transition temperature of LCST and realize macroscopic phase separation at low to moderate temperature and concentration. Minor modifications in the chemical structure of crown ethers (benzo-21-crown-7, B21C7s) can effectively control the thermo-responsive properties.

Structure and Dynamic Behavior of the Na–Crown Ether Complex in the Graphite Layers Studied by DFT and 1H NMR

Diffusion of alkali metals in graphite layers is significant for the chemical and electrochemical properties of graphite intercalation compounds (GICs). Crown ethers co-intercalate into graphite with alkali metal (Na and K) cations and form ternary GICs. The structures and molecular dynamics of 15-crown-5 and 18-crown-6 ether coordinating to Na+ or K+ in GICs were investigated by DFT calculations and 1H solid state NMR analyses. DFT calculations suggest a stacked structure of crown ether–metal complex with some offset. 1H NMR shows two kinds of molecular motions at room temperature: isotropic rotation with molecular diffusion and axial rotation with fluctuation of the axis. The structure and dynamics of crown ether molecules in GIC galleries are strongly affected by the geometry of the crown ether molecules and the strength of the interaction between alkali metal and ligand molecules.

Synthesis of SPR Nanosensor using Gold Nanoparticles and its Application to Copper (II) Determination

This research describes a colorimetric assay for Cu (II) ions that is highly selective over other metal ions. It is based on the measurement of changes in the surface plasmon resonance absorbance (at 525 nm) of gold nanoparticles (Au NPs) modified with 1,7-diaza-15-crown-5 (Crown-Au NPs). The unique structure of crown ethers and presence of heteroatoms enable the crown-Au NPs to recognize very low concentrations of Cu (II) ions. After aggregation, the surface plasmon absorption band has a red shift so that the nanoparticle solution shows a violet color. The TEM images data show that this color change is a result of crown-Au NPs aggregation upon addition of Cu (II), In contrast, other metal ions Al3+, Ca2+, Cd2+, Co2+, Cr3+, Ag+, Fe2+, Fe3+, Hg2+, K+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, and Zn2+ do not aggregate. The recognition mechanism is attributed to the formation of a sandwich (2+1) between the Cu (II) ion and two diaza-15-crown-5 moieties that are attached to separate nanoparticles. This simple and fast method can be used to determine the Cu (II) ions with a detection limit as low as 200 nM.

Synthesis, photochemical and luminescent properties of ortho-hydroxystyrylquinazolinone-linked benzocrown ethers

Abstract Photoinduced transformations of (E)-2-(2-hydroxystyryl)quinazolinone-linked benzo[15(18)]crown-5(6) ethers in solutions have been studied by using UV–vis absorption and NMR spectroscopy. These crown ethers were found to have dual emission at 520 and 650 nm, associated with proton-transfer tautomer emission (ESIPT-luminescence) as a rare case of excited-state proton-transfer reaction in the non-pseudocyclic chromophoric systems. It was established also, that the organic bases affect the luminescence intensity of solutions of these compounds in the 550–650-nm wavelength range. An X-ray crystallography analysis of molecular structures of crown ethers and their complexes in crystals has been carried out. The fact of reversible photo/thermal E-Z isomerization in DMF and Et3N for these macroheterocyclic compounds has been confirmed. An opportunity to control the photochemical isomerization rate of quinazolinone 2-(hydroxyphenyl)ethenyl derivatives by changing pH of the medium has been demonstrated.

Invariom-model refinement and Hirshfeld surface analysis of well-ordered solvent-free dibenzo-21-crown-7.

Crown ethers and their supramolecular derivatives are well-known chelators and scavengers for a variety of cations, most notably heavier alkali and alkaline-earth ions. Although they are widely used in synthetic chemistry, available crystal structures of uncoordinated and solvent-free crown ethers regularly suffer from disorder. In this study, we present the X-ray crystal structure analysis of well-ordered solvent-free crystals of dibenzo-21-crown-7 (systematic name: dibenzo[b,k]-1,4,7,10,13,16,19-heptaoxacycloheneicosa-2,11-diene, C22H28O7). Because of the quality of the crystal and diffraction data, we have chosen invarioms, in addition to standard independent spherical atoms, for modelling and briefly discuss the different refinement results. The electrostatic potential, which is directly deducible from the invariom model, and the Hirshfeld surface are analysed and complemented with interaction-energy computations to characterize intermolecular contacts. The boat-like molecules stack along the a axis and are arranged as dimers of chains, which assemble as rows to form a three-dimensional structure. Dispersive C-H...H-C and C-H...π interactions dominate, but nonclassical hydrogen bonds are present and reflect the overall rather weak electrostatic influence. A fingerprint plot of the Hirshfeld surface summarizes and visualizes the intermolecular interactions. The insight gained into the crystal structure of dibenzo-21-crown-7 not only demonstrates the power of invariom refinement, Hirshfeld surface analysis and interaction-energy computation, but also hints at favourable conditions for crystallizing solvent-free crown ethers.

Odd-even alternation in molecular structure and self-assembling of some macrocyclic polyethers

Abstract It was found that the alternation of the melting points of 3 n -crown- n retains its amplitude within a large range of the number of oxygen atoms ( n = 4–8) in the crown's ring. This behavior is different from that observed for the compounds having n -alkyl chain, where the odd-even effect gradually disappears with increasing number of carbon atoms in the chain. So, the molecular structures of crown ethers containing in their rings even or odd number of oxygen atoms essentially differ from each other and the differences do not disappear when the ring increases. On the basis of temperature behavior of the increment of orientational entropy it was found that in liquid 12-crown-4 and 15-crown-5, the molecules self-organize into entities where the molecules are arranged in a head-to-tail way, while the molecules of 18-crown-6 are behaving quite differently: self-assemblies with antiparallel orientation of the molecular dipoles are predominant.

Synthesis and characterization of novel substituted and cyclic benzoquinone derivatives

ABSTRACTNovel substituted benzoquinone compounds were synthesized from the reactions of p-chloranil and p-fluoranil with some thiols, amines, and diols in different reaction media. Interesting cyclic compounds like crown ether structures were obtained. The structures of all compounds were characterized by spectroscopic methods and microanalysis.

Ab initio molecular dynamics investigation of proton delocalization in crown ether complexes with H3O+ and NH4 +

The simple structure of crown ethers has found a wide range of applications in macrocyclic chemistry, largely due to its ability to capture positively charged ions either in atomic or molecular state. In the present work, ab initio molecular dynamics calculations are performed to characterize the host–guest interactions and conformational dynamics of the complexes formed by the H3O+ and NH4 + cations with the native crown ethers 15-crown-5 and 18-crown-6. A particular focus is set on the proton delocalization effects unveiled in recent spectroscopy experiments for some of these complexes under well-defined isolated (solvent-less) conditions. The calculations confirm that the infrared signature of these benchmark crown ether complexes provides a sensitive probe for proton delocalization. The ab initio study also shows that proton delocalization occurs for the H3O+ host (and not for NH4 +), provided that the size of the crown ring allows for tight H-bonding interactions between the cationic guest and the crown ether, leading short H2O···H+···O (crown) bonds.

Percolative Behavior Models Based on Artificial Neural Networks for Electrical Percolation of AOT Microemulsions in the Presence of Crown Ethers as Additives

Abstract A series of models, based on artificial neural networks, of the percolative behaviour of AOT microemulsions in the presence of crown ethers as additives have been developed. Input variables, related to the chemical structure of crown ethers and their packing with surfactant film, have been selected. As a result, a model has been chosen with a good forecast capability for percolation threshold of such microemulsions.