Crown Ether Complexes Research Articles

Conductometric Study of Complexation of Macrocyclic Compounds with Zinc(II) and Copper(II) Ions in Aqueous-Organic Solvent Mixtures

The conductance behavior of Zn2+ and Cu2+ and their complexes with two ligands (crown ethers) have been inspected in 10, 20, 30, and 40% DMF–water mixed solvent at 298.15, 308.15, 318.15, and 328.15 K. The conductance study indicates a 1 : 1 complexation mode amongst the metal ions and ligands hereby studied. The order of stability constants with crown ethers was found to be Cu(II) > Zn(II). The stability constant for Zn2+ ion with crown ether complexes in 10 and 40 wt % solvent composition varies in the order of benzo-18-crown-6 > benzo-15-crown-5. The stability constant for Cu2+ ion with crown ether complexes in 10% solvent composition varies in the order of benzo-18-crown-6 > benzo-15-crown-5, and for 40% solvent composition, it is benzo-18-crown-6 > benzo-15-crown-5. The enthalpy and the entropy of complexation were estimated from the variation of stability constants with respect to the variation of temperature. The observed results elicit that the complexation is enthalpy stabilized, but entropy destabilized.

Conformation of K+(Crown Ether) Complexes Revealed by Ion Mobility-Mass Spectrometry and Ultraviolet Spectroscopy.

The conformation and electronic structure of dibenzo-24-crown-8 (DB24C8) complexes with K+ ion were examined by ion mobility-mass spectrometry (IM-MS), ultraviolet (UV) photodissociation (UVPD) spectroscopy in the gas phase, and fluorescence spectroscopy in solution. Three structural isomers of DB24C8 (SymDB24C8, Asym1DB24C8, and Asym2DB24C8) in which the relative positions of the two benzene rings were different from each other were investigated. The IM-MS results at 86 K revealed a clear separation of two sets of conformers for the K+(SymDB24C8) and K+(Asym1DB24C8) complexes whereas the K+(Asym2DB24C8) complex revealed only one set. The two sets of conformers were attributed to the open and closed forms in which the benzene-benzene distances in the complexes were long (>6 Å) and short (<6 Å), respectively. IM-MS at 300 K could not separate the two conformer sets of the K+(SymDB24C8) complex because the interconversion between the open and closed conformations occurred at 300 K and not at 86 K. The crown cavity of DB24C8 was wrapped around the K+ ion in the complex, although the IM-MS results availed direct evidence of rapid cavity deformation and the reconstruction of stable conformers at 300 K. The UVPD spectra of the K+(SymDB24C8) and K+(Asym1DB24C8) complexes at ∼10 K displayed broad features that were accompanied by a few sharp vibronic bands, which were attributable to the coexistence of multiple conformers. The fluorescence spectra obtained in a methanol solution suggested that the intramolecular excimer was formed only in K+(SymDB24C8) among the three complexes because only SymDB24C8 could possibly assume a parallel configuration between the two benzene rings upon K+ encapsulation. The encapsulation methods for K+ ion (the "wraparound" arrangement) are similar in the three structural isomers of DB24C8, although the difference in the relative positions of the two benzene rings affected the overall cross-section. This study demonstrated that temperature-controlled IM-MS coupled with the introduction of appropriate bulky groups, such as aromatic rings to host molecules, could reveal the dynamic aspects of encapsulation in host-guest systems.

Crown ethers as shift reagents in peptide epimer differentiation \u2013conclusions from examination of ac-(H)FRW-NH2 petide sequences

Crown ethers with different ring sizes and substituents (18-crown-6, dibenzo-18-crown-6, dicyclohexano-18-crown-6, a chiral tetracarboxylic acid-18-crown-6 ether, dibenzo-21-crown-7, and dibenzo-30-crown-10) were evaluated as shift reagents to differentiate epimeric model peptides (tri-and tetrapeptides) using ion mobility mass spectrometry (IM-MS). The stable associates of peptide epimers with crown ethers were detected and examined using traveling-wave ion mobility time-of-flight mass spectrometer (Synapt G2-S HDMS) equipped with an electrospray ion source. The overall decrease of the epimer separation upon crown ether complexation was observed. The increase of the effectiveness of the microsolvation of a basic moiety - guanidine or ammonium group in the peptide had no or little effect on the epimer discrimination. Any increase of the epimer separation, which referred to the specific association mode between crown substituents and a given peptide sequence, was drastically reduced for the longer peptide sequence (tetrapeptide). The obtained results suggest that the application of the crown ethers as shift reagents in ion mobility mass spectrometry is limited to the formation of complexes differing in stoichiometry rather than it refers to a specific coordination mode between a crown ether and a peptide molecule.

Specific Host-Guest Interactions in the Crown Ether Complexes with K+ and NH4+ Revealed from the Vibrational Relaxation Dynamics of the Counteranion.

The specific host-guest interactions in the corresponding complexes of K+ and NH4+ with typical crown ethers were investigated by using FTIR and ultrafast IR spectroscopies. The counteranions, i.e., SCN-, were employed as a local vibrational probe to report the structural dynamics of the complexation. It was found that the vibrational relaxation dynamics of the SCN- was strongly affected by the cations confined in the cavities of the crown ethers. The time constant of the vibrational population decay of SCN- in the complex of NH4+ with the 18-crown-6 was determined to be 6 ± 2 ps, which is ∼30 times faster than that in the complex of K+ with the crown ethers. Control experiments showed that the vibrational population decay of SCN- depended on the size of the cavities of the crown ethers. A theoretical calculation further indicated that the nitrogen atom of SCN- showed preferential coordination to the K+ ions hosted by the crown ethers, while the NH4+ can form hydrogen bonds with the oxygen atoms in the studied crown ethers. The geometric constraints formed in the complex of crown ethers can cause a specific interaction between the NH4+ and SCN-, which can facilitate the intermolecular vibrational energy redistribution of the SCN-.

Thermodynamics of complexation and membrane activity of crown ethers

Thermodynamics of complexation and membrane activity of crown ethers

Cover Feature: Selective Phase Transfer Reagents (OxP‐crowns) for Chromogenic Detection of Nitrates Especially Ammonium Nitrate (Chem. Eur. J. 58/2020)

A color-based detector for ammonium nitrate consists of crown ether-appended oxoporphyrinogens, the OxP-Crowns, which extract ion pairs into an organic phase based on cation binding at crown ether and anion complexation. Selective mauve chromogenic response is observed when ammonium nitrate, commonly used in improvised explosive devices, is extracted from water to chloroform providing a simple test. As illustrated, a network of responses is found when considering other anions and aqueous phase pH. More information can be found in the Full Paper by J. P. Hill et al. on page 13177.

Evaluation of Chemical Bonding in Actinyl(VI/V) Oxo-Crown-Ether Complexes for Actinide Series from Uranium to Curium.

The separation and management of nuclear waste is one of the problems that needs to be solved urgently, so finding a new radiation-proof and durable extractant to deal with nuclear waste is a difficult but desirable task. Since the successful isolation of the first pentavalent plutonium crown ether complex recently (Wang et al. CCS Chem. 2020, 2, 425-431), complexes with actinyl(V/VI) inserted into the cavity of 18-crown-6 ether (oxo-18C6), as well as their bonding character, need to be explored. Here we present a series of novel crown ether complexes containing actinyl(V/VI) and oxo-18C6 via computational prediction and analysis. On the basis of the calculations, actinyl(V/VI) are thermodynamically feasible and can be stabilized by oxo-18C6 ligand via six dative bonds between An ions and the oxo-18C6 O atoms in the "insertion" structure of [AnO2(18C6)]2+/+ complexes. The stability of actinyl(VI) species generally falls at minor actinides, ascribed to the reduced highest possible oxidation states of curium, which is mainly attributed to the mixing of bonding orbitals and non-bonding orbitals as well as the increase of occupation on partially 5f antibonding orbitals. It is found that the interactions between the actinyl(V/VI) and oxo-18C6 are mainly electronic interactions, with the well-known covalency contributions generally decreasing from uranium to curium due to energy degeneracy and spatial orbital contraction. This work would give a basic understanding of the coordination chemistry of actinyl(V/VI), which also provides inspirations on the design of new extractants for actinide separations.

Experimental and theoretical insight into the extraction mechanism, kinetics, thermodynamics, complexation and radiolytic stability of novel calix crown ether in ionic liquid with Sr2+

A comparative evaluation was carried out for the extraction of Sr2+ using novel calix crown ether in molecular diluent and in ionic liquid. Though the trend in extraction profiles was found to be similar for both the systems, still, almost 5 times higher distribution ratio (D) values were observed in ionic liquid. The speciation studies revealed that; neutral Sr (NO3)2. DHCC species was formed in dodecane and the extraction followed through ‘solvation’ mechanism. However, ionic liquid medium (IL), anionic species, [Sr(NO3)3. DHCC]− was found to be predominating indicating ‘anion exchange’ mechanism. The slower kinetics of extraction in IL was attributed to the high viscosity of IL. The extraction process was found to be spontaneous, endothermic and entropy driven.IL based system was found to be radiolytically more stable compared to the molecular diluent (Mol dil) based system. The electron paramagnetic resonance (EPR) spectroscopic investigation revealed the formation of oxygen centered radical with orthorhombic symmetry (gx = 2.00105, gy = 2.00475, gz = 2.00835) in irradiated ligand. The density functional theoretical (DFT) calculation was utilized to investigate the complexation and speciation in detail in microscopic level.

Synthesis, structure, supramolecular architecture and Hirshfeld surface analysis of 4-aminobenzene-1-sulfonic acid with 18-crown-6

Abstract (4-Ammoniobenzene-1-sulfonate-18-crown-6)2.9.5(H2O) single crystals were grown by the slow evaporation method. The characteristic functional groups present in the molecules are identified by FT-IR analysis. The direct band gap energy is estimated by Kubelka–Munk algorithm and the complex qualifies as a wide-band gap material. Photoluminescence exhibits fluorescent emission of title complex in the solid-state at room temperature. The crystal structure is elucidated by single-crystal X-ray diffraction analysis and the crown ether complex belongs to the triclinic system with a centric space group Pī. Inter- and intramolecular hydrogen-bonding interactions and weak van der Waals forces construct the supramolecular architecture in the crystal packing. The organic 4-aminobenzene-1-sulfonic acid exists as a zwitterion and interacts directly via N H•••O hydrogen bonds with the cavity of 18-crown-6 (18C6). Molecular interactions are analyzed by Hirshfeld surfaces, derived from single-crystal XRD data. Fingerprint plots of Hirshfeld surfaces are used to locate and analyze the percentage of hydrogen bonding interactions.

Radiation-induced macrocycle cleavage in crown ether complexes with Sr(II) and Y(III) chlorides: A comparative study

Macrocyclic 18-crown-6⋅SrCl2 and 18-crown-6⋅YCl3⋅4.25H2O complexes were synthesized, characterized by FTIR and DSC/TGA analysis and exposed to X-rays irradiation to study their resistance to polyether ring cleavage at early radiolysis stages by using EPR spectroscopy. Yttrium complex was found to be less stable in comparison with that of strontium as evidenced by a higher fraction of acyclic radicals resulted from the macrocycle destruction. An analysis of conformationally sensitive regions of FTIR spectra of 18-crown-6⋅YCl3⋅4.25H2O points to the strong distortion of the macrocycle symmetry that is one of the probable factors affecting the radiolytic cleavage of the polyether ring. The results obtained in the present study contribute to theoretical framework required to develop a radiation stable macrocyclic extractant for separation of the Sr/Y radionuclides.

Empirical Models of Stability of Crown Ether Complexes with Alkaline and Alkaline-Earth Metals in Selected Pure Solvents

An approach to predict the stability constants of coronates from the properties of solvents, cations, and crown ethers has been developed based on exploratory and neural network methods for mathematical modeling of equilibria in solutions. Exploratory (factor, cluster, discriminant, canonical, decision trees), regression, and neural network (supervised and Kohonen network) models of the stability of crown ethers (12С4, 13С4, 14С4, 15С4, 15С5, 18С6, 21С7, 24С8, B12C4, B15C5, CH15C5, CH18C6, DCH18C6, DCH21C7, DB18C6, DB21C7, DB24C8, DB27C9, and DB30C10) complexes with cations of alkali (Li+, Na+, K+, Cs+, Rb+) and alkaline-earth (Ca2+, Sr2+, Ba2+) metals in aqueous and non-aqueous (acetone, acetonitrile, dimethyl sulfoxide, methanol, pyridine, dimethylformamide, dioxane, propylene carbonate, 1,2-dichloroethane, and nitrobenzene) solutions have been developed according to the properties of solvents (diameter of solvent molecule, Kamlet–Taft parameter, Dimroth–Reichardt parameter, dielectric constant), crown ethers (Balaban topological index), and cations (cation diameter) at 298.15 K.

Small Crown-Ether Complexes as Molecular Models for Dihydrogen Adsorption in Undercoordinated Extraframework Cations in Zeolites

1:1 metal complexes of small crown-ethers are structurally similar to extraframework sites in metal-exchanged zeolites. Using ab initio calculations, we show that adsorbed molecular hydrogen follow...

Ionic Dopant-Encapsulating Single-Walled Carbon Nanotube Films with Metal-Like Electrical Conductivity.

Heavy doping is inevitable for utilizing single-walled carbon nanotubes for wiring. However, the electrical conductivity of their films is currently as low as one tenth of the films made from typical metal pastes. Herein we report on metal-comparable electrical conductivity from single-walled carbon nanotube network films. We use ionic liquids and crown ether complexes for p-type and n-type doping, respectively. The encapsulation of counterions into carbon nanotubes promotes the conductivities in the range of 7000 S cm-1 , approximately ten times larger than those of undoped films.

Investigation of photophysical behaviours and antimicrobial activity of novel benzo-15-crown-5 substituted coumarin and chromone derivatives

Two different series of crown ether compounds (4-11) were synthesized by the reactions of 4′,5′-bis(bromomethyl)benzo-15-crown-5 (3) and 4′-amino-benzo-15-crown-5 with hydroxycoumarin and chromone derivatives. Coumarin-crown ether compounds (4 and 5) were synthesized by the reactions of 4′,5′-bis(bromomethyl)benzo-15-crown-5 (3) with 4-hydroxycoumarin and 7-hydroxycoumarin. Chromone-crown ether compounds (6-11), were synthesized by the condensation reactions of 4′-amino-benzo-15-crown-5 with 3-formylchromone and 6-methyl-3-formylchromone in different solvent media. Sodium and potassium complexes (4a-11a, 4b-11b) of new coumarin and chromone substituted benzo-15-crown-5 (B15C5) ligands (4-11) were prepared with NaSCN and KSCN, respectively. The syntheses of the novel crown ether compounds (4-11) and complexes (4a-11a, 4b-11b) were elucidated by the elemental analysis, FTIR, 1H NMR, 13C NMR and MS spectral data. The metal selectivities and effects of metal cations (Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Ag+, Al3+, Cu2+, Zn2+, Ni2+, Pb2+, Fe3+, Cr3+) to the new crown ether compounds (4-11) were investigated by the absorption and fluorescence spectra. In addition, all of these substances were examined for antibacterial activity against pathogenic strains Listeria monocytogenes 4b, Staphylococcus aureus, Escherichia coli, Salmonella typhi H, Bacillus cereus, Micrococcus luteus, Shigella dysenteria type 2, Staphylococcus epidermidis, Proteus vulgaris, Klebsiella pneumonia sp., Serratia marcescens sp. and antifungal activity against Candida albicans.

Crown Ethers as Electrolyte Additives To Modulate the Electrochemical Potential of Lithium Organic Batteries

Organic batteries have attracted much attention because of their flexibility, high-power densities, and highly designable structures of electrode-active materials. The electrochemical potential of the batteries can be modulated using different organic redox species or by structural modification of the redox unit centers. In this study, the electrochemical potential of lithium organic radical batteries is modulated, without the structural modification of the redox unit centers. Two different crown ethers, 12-crown-4 (12C4) and 15-crown-5 (15C5), served as electrolyte additives to increase the electrochemical potential of the batteries. An average discharge voltage can be increased to 3.90 V through the electrolyte system using various concentrations of the electrolyte salt and crown ethers. The addition of 1 equiv of 12C4 to the Li|0.25 M LiClO4-ethylene carbonate/diethyl carbonate (= 1/1, v/v|poly(2,2,6,6-tetramethylpiperidin-1-oxy-4-yl methacrylate) cells significantly improved the capacity retention up to 21% after 300 cycles at a current rate of 3C. Furthermore, the structures and system energies of the lithium–crown ether complexes are investigated using density functional theory calculations.

Calculation of Lithium Isotope Effects in Extraction Systems with Benzo-15-crown-5 and Its Derivatives

With taking into account the β-factor value of the lithium ion aqua complex found earlier, the single stage extraction coefficient of isotope separation (α) of the 6Li–7Li pair has been calculated for the extraction system containing the benzo-15-crown-5–Li+ (H2O)Cl– complex in the organic phase, which corresponds to a real extraction process. Similar calculations have been carried out for other anions, as well as for various benzo-15-crown-5 derivatives with varying the number and type of donor atoms and different substituents in the benzene ring. Quantum-chemical calculations of the vibrational frequencies of the isotopic forms of the crown ether complex were performed using the Firefly program with the RHF/6-311++G** basis set. It has been shown that the isotope separation factor in this case is lower than in the case of the anhydrous benzo-15-crown-5–Li+Cl– complex and the model benzo-15-crown-5–Li+ (H2O) complex.

Determination of crown ether complexation with metal ıons by application Job’s Plot method to conductometry

Bu çalışma kapsamında benzo-tiyo ve benzo-okso taç eterler ile metal iyonları arasındaki iyon-dipol etkileşmeleri Job’s Plot yönteminin kondüktometriye uyarlanmasıyla belirlendi (Çözücü sistemi: %50 Asetonitril/su). Daha önce verilen mikrodalga sentez yöntemi kullanılarak yeniden sentezlenen U1 (bis(1,2-dibenzo) oktatiyo tetrakarbonil-29-crown-6), U2 (bis(1,2-dibenzo) tetratiyo tetrakarbonil-29-crown-6) taç eterlerinin NaCl, KCl, MgCl2, CaCl2, ZnCl2, FeSO4, AgNO3, CoCl2 metal tuzlarıyla komplesleşmeleri incelendi. Taç eter-katyon kompleksinin kompleksleşme oranı, kompleksleşme sabiti (Ke) ve Serbest Gibbs Enerjisi (ΔGθ ) hesaplandı. Kondüktometri ile gerçekleştirilen çalışmalara göre U1 bileşiği için kompleksleşme sabiti Na+ &amp;gt; Zn2+ &amp;gt; Ca2+ &amp;gt; Ag+ &amp;gt; K+ &amp;gt; Mg2+ &amp;gt; Co2+ &amp;gt; Fe2+ yönünde azalırken, U2 bileşiği için Zn2+ &amp;gt; Fe2+ &amp;gt; Na+ &amp;gt; K+ &amp;gt; Co2+ &amp;gt; Ag+ &amp;gt; Ca2+ &amp;gt; Mg2+ yönünde değiştiği gözlemlenmiştir. Bu çalışma sonuçlarına göre taç eterler metal sensörü, biyoorganizmalardaki enzimler için inhibitör veya aktivatör ve sanayi-çevre uygulamalarında metal iyonlarının giderimi için kullanılabilirler.

Record Low Ionization Potentials of Alkali Metal Complexes with Crown Ethers and Cryptands.

Electronic properties of series of alkali metals complexes with crown ethers and cryptands were studied via DFT hybrid functionals. For [M([2.2.2]crypt)] (M=Li, Na, K) extremely low (1.70-1.52 eV) adiabatic ionization potentials were found. Such low values of ionization energies are significantly lower than those of alkali metal atoms. Thus, the investigated complexes can be defined as superalkalis. As a result, our investigation opens up new directions in the designing of chemical species with record low ionization potentials and extends the explanation of the ability of the cryptates and alkali crown ether complexes to stabilize multiple charged Zintl ions.

Supramolecular Fe3O4@PEG/−diaza crown ether@Ni: a novel magnetically reusable nano catalyst for the clean synthesis of 2‐aryl‐2,3‐dihydroquinazolin‐4(1H)‐ones

Ni@diaza crown ether complex supported on magnetic nanoparticle was provided by grafting technique. The catalytic activity of Fe3O4@diaza crown ether@Ni was explored through one‐pot synthesis of 2,3‐dihydroquinazolin‐4(1H)‐ones and it was used as an efficient and recoverably constant nanocatalyst. FT‐IR, SEM, TEM, XRD, BET, ICP, EDS, and TGA techniques were employed to specify the nanocatalyst. This heterogeneous catalyst demonstrated acceptable recyclability and could be used again several times with no considerable loss of its catalytic activity.

New deep eutectic solvents composed of crown ether, hydroxide and polyethylene glycol for extraction of non-basic N-compounds

Here we firstly report a series of new deep eutectic solvents (DESs) induced by small amounts of crown ether complex and mainly formed by polyethylene glycol. These DESs not only presented the ultra-deep extraction of non-basic N-compounds from fuel oils, but also opened up the possibility of other new applications in chemistry and materials science.