Addition Of Crown Ethers Research Articles

Porous Liquids as Electrolyte: A Case Study of Li+ and Mg2+ Ion Transport in Crown Ether-Based Type-II Porous Liquids

We demonstrated an enhanced ion transport properties of type-II porous liquid-based electrolyte in which crown ether provides internal porosity and are capable of coordinating and transporting Li+ and Mg2+ ions. We investigated the solvation structure and transport properties of the porous liquid electrolytes with different functional groups and cavity sizes. Among the electrolytes studied, the 12-crown-4 (12C4)-based porous liquid electrolyte exhibited the most enhanced ionic conductivity due to size match between the crown ether cavity and the Li+ ion. Nuclear magnetic resonance and Fourier transform infrared analyses revealed that addition of crown ethers reduces the Li+ ion–solvent interaction, resulting in the formation of Li-crown ether complexes. Molecular simulations complement such observations by describing the detailed solvation environment at molecular scale, including complexation between Li+ and Mg2+ ions and 12C4. The strategy described here using crown ether-based porous liquids should be applicable to design versatile electrolytes for various metal-ion batteries.

Sodium Aminotroponiminates: Ligand‐Induced Disproportionation, Mixed‐Metal Compounds, and Exceptional Activity in Polymerization Catalysis

AbstractSodium complexes of aminotroponiminate (ATI) ligands have been reacted with a range of neutral donor ligands. Upon addition of crown ethers, they undergo an unusual ligand‐induced disproportionation reaction with formation of [Na(ATI)2]− sodiate complex anions. The same structural motif has also been found in the first well‐defined mixed‐metal ATI complexes, which have been accessed starting from monometallic sodium and potassium species. The mixed‐metal compounds confirm the possibility of ATIs to act as ditopic ligands. Using the polymerization of ϵ‐caprolactone as a model system, structure‐reactivity‐relationships in sodium and mixed‐metal ATI compounds have been studied by comparing the reactivity of [Na(ATI)] and [Na(ATI)2]− structural motifs. These studies revealed trends in the catalyst activity depending on the nuclearity of the complex and the substitution pattern at the ATI ligand. Exceptionally high activities were obtained for dinuclear sodium sodiates of type [Na(crown)2][Na(ATI)2], making them the most active alkali metal initiators for this reaction. The organometallic and polymeric compounds presented in this work have been characterized by techniques including (VT‐)NMR spectroscopy, single‐crystal X‐ray diffraction, gel permeation chromatography, mass spectrometry, and DFT calculations.

The Tris(pentafluoroethyl)silanide Anion.

Tris(pentafluoroethyl)silane, which is conveniently accessible by the treatment of Si(C2 F5 )3 X (X=Cl, Br) with Bu3 SnH, was successfully employed for hydrosilylation reactions. In the presence of a palladium catalyst, hydrosilylation of phenylacetylene with Si(C2 F5 )3 H affords the product of an α-addition whereas the reaction of trimethylsilylacetylene with the silane leads to the β-trans product. Tris(pentafluoroethyl)silane can be deprotonated by sterically demanding bases such as lithium diisopropylamide at low temperatures to give the corresponding silanide ion. The addition of crown ethers or cryptands to this highly reactive species enabled the isolation and characterization of salt-like tris(pentafluoroethyl)silanide at room temperature.

Rapid and specific detection of urea nitrate and ammonium nitrate by electrospray ionization time‐of‐flight mass spectrometry using infusion with crown ethers

Urea nitrate (UN) and ammonium nitrate (AN) are fertilizer-based explosives that are commonly used in improvised munitions and can have highly destructive effects. Because they are in the form of salts, their relatively low volatility makes them difficult to detect at trace levels. In addition, these salts readily undergo metathetic reactions in water to form urea, ammonium and nitrate, which are ubiquitous in the environment. Thus, selective methods are needed for their detection. In this study, a procedure was developed to detect UN and AN in non-aqueous environments by positive ion electrospray ionization mass spectrometry through the addition of 18-crown-6. The method is sensitive, with detection limits under 2 μM, and selective. The procedure is capable of differentiating urea from uronium ions (protonated urea) and a mixture of urea and AN did not interfere with the UN signal. The procedure is quite versatile and the addition of crown ethers to the sample matrix does not interfere with the detection of high explosives in the negative ionization mode. Experimental results are presented on the utilization of the method in the detection of UN and AN on various surfaces. Semi-quantitative studies showed that AN and UN can be detected at trace levels following finger transfer and a series of studies were performed to demonstrate the effect of various interferences. The results show the method to be a quick and robust procedure for trace detection.

Synergistic Enhancement and Separation of Zirconium(IV) and Hafnium(IV) with 3-Phenyl-4-Benzoyl-5-Isoxazolone in the Presence of Crown Ethers

3-Phenyl-4-benzoyl-5-isoxazolone (HPBI) was synthesized and examined with regard to the synergistic solvent extraction behavior of zirconium(IV) and hafnium(IV) in the presence of various crown ethers (CEs), namely, 18-crown-6 (18C6), dicylohexano-18-crown-6 (DC18C6) and benzo-15-crown-5 (B15C5) from hydrochloric acid solutions. The results demonstrated that zirconium(IV) and hafnium(IV) were synergistically extracted into chloroform with mixtures of HPBI and CEs as ZrO(PBI)2 · CE and HfO(PBI)2 · CE, respectively. The complexation strength follows the order DC18C6 >18C6 > B15C5. The addition of CEs not only enhances the extraction efficiency of zirconium(IV) and hafnium(IV) but also significantly, especially in the presence of B15C5, improves the selectivity (Zr/Hf = 4.73) between these metal ions as compared to HPBI alone (Zr/Hf = 2.09). On the other hand, selectivity has been moderately decreased by the addition of 18C6 or DC18C6 to the metal-chelate system.

Membrane Topology of a 14-mer Model Amphipathic Peptide: A Solid-State NMR Spectroscopy Study

We have investigated the interaction between a synthetic amphipathic 14-mer peptide and model membranes by solid-state NMR. The 14-mer peptide is composed of leucines and phenylalanines modified by the addition of crown ethers and forms a helical amphipathic structure in solution and bound to lipid membranes. To shed light on its membrane topology, 31P, 2H, 15N solid-state NMR experiments have been performed on the 14-mer peptide in interaction with mechanically oriented bilayers of dilauroylphosphatidylcholine (DLPC), dimyristoylphosphatidylcholine (DMPC), and dipalmitoylphosphatidylcholine (DPPC). The 31P, 2H, and 15N NMR results indicate that the 14-mer peptide remains at the surface of the DLPC, DMPC, and DPPC bilayers stacked between glass plates and perturbs the lipid orientation relative to the magnetic field direction. Its membrane topology is similar in DLPC and DMPC bilayers, whereas the peptide seems to be more deeply inserted in DPPC bilayers, as revealed by the greater orientational and motional disorder of the DPPC lipid headgroup and acyl chains. 15N{31P} rotational echo double resonance experiments have also been used to measure the intermolecular dipole-dipole interaction between the 14-mer peptide and the phospholipid headgroup of DMPC multilamellar vesicles, and the results indicate that the 14-mer peptide is in contact with the polar region of the DMPC lipids. On the basis of these studies, the mechanism of membrane perturbation of the 14-mer peptide is associated to the induction of a positive curvature strain induced by the peptide lying on the bilayer surface and seems to be independent of the bilayer hydrophobic thickness.

Insights on the Interactions of Synthetic Amphipathic Peptides with Model Membranes as Revealed by 31P and 2H Solid-State NMR and Infrared Spectroscopies

We studied the interaction between synthetic amphipathic peptides and model membranes by solid-state NMR and infrared spectroscopies. Peptides with 14 and 21 amino acids composed of leucines and phenylalanines modified by the addition of crown ethers were synthesized. The 14-mer and 21-mer peptides both possess a helical amphipathic structure. To shed light on their membrane interaction, 31P and 2H solid-state NMR experiments were performed on both peptides in interaction with dimyristoylphosphatidylcholine vesicles in the absence and presence of cholesterol, dimyristoylphosphatidylglycerol vesicles, and oriented bicelles. 31P NMR experiments on multilamellar vesicles reveal that the dynamics and/or orientation of the polar headgroups are weakly yet markedly affected by the presence of the peptides, whereas 31P NMR experiments on bicelles indicate no significant changes in the morphology and orientation of the bicelles. On the other hand, 2H NMR experiments on vesicles reveal that the acyl chain order is affected differently depending on the membrane lipidic composition and on the peptide hydrophobic length. Finally, infrared spectroscopy was used to study the interfacial region of the bilayer. Based on these studies, mechanisms of membrane perturbation are proposed for the 14-mer and 21-mer peptides in interaction with model membranes depending on the bilayer composition and peptide length.

Liquid–liquid–liquid phase microextraction of aromatic amines in water using crown ethers by high-performance liquid chromatography with monolithic column

Liquid–liquid–liquid phase microextraction (LLLME) coupled with high-performance liquid chromatography (HPLC) for the analysis of some aromatic amines is described. These compounds were extracted from 4.0 mL aqueous sample that adjusted to pH 13 with, NaOH–NaCl buffer solution (donor phase, P 1) into an organic phase (P 2) 150 μl benzyl alcohol and ethyl acetate (2:1) and then back extracted into a microdrop of aqueous acceptor phase (P 3), adjusted at pH 2, with Na 2HPO 4–H 3PO 4 buffer solution. The extraction time, T 1 (from P 1 to P 2) was 20 min and T 2 (from P 2 to P 3) was 1 min. Different crown ethers as complexing agents for amines were added to the acceptor phase to improve the extraction time. Factors such as organic solvents, extraction times, and addition of crown ethers to acceptor phase and stirring rate were optimised. The method was applied for determination of aromatic amines in wastewater samples. Enrichment factors ranged from 184.5 to 389.7. The linearity range was from 3 to 1000 ng/ml and the detection limits varied from 0.8 to 1.80 ng/ml. Relative standard deviations (%, n = 5) were found (at S/ N 3) in the range of 1.9 to 10.1. All experiments were carried out at room temperature, 22 ± 0.5 °C.

Radical clocks and electron transfer. Comparison of crown ether effects on the reactivity of potassium and magnesium towards 1-bromo-2-(3-butenyl)benzene. The incidence of homogeneous versus heterogeneous electron transfer on selectivity

The reaction of the title precursor of the aryl radical clock 1-bromo-2-(3-butenyl)benzene, 1Br, towards potassium and magnesium in THF was studied in the presence and absence of various additives, at ambient and low temperatures. The additives were cis-dicyclohexano-18-crown-6 or tert-butyl alcohol; the first one to render soluble potassium by forming its alkalide, the second to distinguish carbanionic from radical cyclization. The addition of 1Br to a THF stirred suspension of potassium pieces yields remarkably low amounts of products resulting from radical cyclization, in contrast to the amounts reported by Bunnett and Beckwith's group for the reaction in 67% ammonia–33% tert-butyl alcohol medium. The amount of cyclized products obtained with potassium pieces in THF is in the same range as that observed in the reaction of magnesium with 1Br in THF. This similarity allows us to discard the earlier triad hypothesis that we proposed to account for the unexpectedly low amounts of cyclized products of aryl halides radical clocks in Grignard reagent formation. The addition of crown ethers to the THF reaction medium induces contrasting effects for potassium and magnesium. A distinctive increase in the radical cyclization is observed for potassium, whereas the addition of crown inhibits the formation of Grignard reagent more efficiently when the solvent is diethyl ether than when it is THF. The observed effects are explained by putting in perspective the metal reactive dissolution with elementary steps occurring in the vicinity of a cathode. The reaction of potassium pieces or magnesium turnings is comparable to the heterogeneous electron transfer occurring at a cathode whereas the reaction of potassium in the presence of crown ether is comparable to homogeneous conditions of electron transfer obtained in redox catalysis. A discussion of the dianion hypothesis for the Grignard reaction of aryl halides is provided and the importance of considering the reactivity of reactive metal dissolution (or organic corrosion) in the framework of recent progress made in the modelling of electrode reactivity is emphasized. This paper shows that caution should be taken when radical clocks are used to study reactions at the metal–solution interface. More specifically, the non-observation of rearranged products from the radical clock (even for the very rapid ones) under these conditions does not necessary imply that there is no radical intermediate along the dominant reaction channel. This pattern of reactivity strongly contrasts with that usually observed when radical clocks are used in homogeneous media. The leading parameters in the rearranged/unrearranged products ratio seem to be the time that the reactive species (radical anions) created by the first electron transfer spend in the close vicinity of this surface, the rate constant of rearrangement of the radical formed by the cleavage of the radical anion and the redox properties of this radical. Copyright © 2005 John Wiley & Sons, Ltd.

Electron Spin Resonance Studies of Kinetic Effects of Substituent and Crown Ether on Intramolecular Sodium Cation Exchange in 2,5-Di-Tert-Amyl- and 2,5-Di-Tert-Butyl-1,4-Benzoquinone Radical Anions

Abstract Upon an addition of crown ethers to a solution of 2,5-di-tert-amyl-1,4-benzoquinone (2,5-DAQ) and 2,5-di-tert-butyl-1,4-benzoquinone (2,5-DBQ) radical anions, the significant broadening of the two-center lines was observed in their electron spin resonance (ESR) spectra. The formation constants for the complexation of sodium cation with three kinds of crown ethers in 2,5-DAQ and 2,5-DBQ radical ion pairs were estimated, and the intramolecular two-site jumping rates of sodium cation complexed with crown ethers were determined. Differential effects of steric and crown ether were found in the intramolecular sodium cation migration. The stabilization of inclusion complex of sodium cation with crown ethers gives rise to the acceleration effects on the rates of intramolecular migration of cation/crown-ether complex. Based on the results, a kinetic explanation for the intramolecular sodium cation migration in the presence of crown ethers was given.

A study of the effect of pH, solvent system, cone potential and the addition of crown ethers on the formation of the monensin protonated parent ion in electrospray mass spectrometry

A systematic investigation has been performed on the effect of pH, cone potential, solvent system and the influence of crown ethers on the relative intensity of the monensin protonated parent ion [M+H]+ in electrospray mass spectrometry (ESI-MS). The analyses were performed on either a triple quadrupole (Quattro-LC) or a quadrupole time-of-flight (Q-tof) mass spectrometer. The pH variation showed that it is possible to detect the protonated ion at low pH. An increase in the cone potential resulted in an increase of the observed signal and the best signal-to-noise was observed at 120 V. The addition of 15-crown-5 and 18-crown-6 ethers to the solution led to an increase of the protonated ion intensity through successful competition of the crown ether for the alkali metal cation. The 15-crown-5 ether, though, showed a distinct disadvantage over the 18-crown-6 ether due to retention of its sodium adduct in the source and detector of the instrument. Acetonitrile–water proved to be the best solvent system for these studies. The best conditions for the 18-crown-6 ether were then applied to an analysis on a Fourier-transform ion cyclotron resonance (BioApex II) mass spectrometer which clearly demonstrated the production of the protonated ion.

Indirect ultraviolet spectrophotometric detection in the ion chromatography of common mono- and divalent cations on an aluminium adsorbing silica gel column with tyramine-containing crown ethers as eluent

The application of laboratory-made aluminium-adsorbing silica gel (Al–Silica) as a cation-exchange stationary phase to ion chromatography–indirect photometric detection (IC–IPD) for common mono- and divalent cations (Li +, Na +, NH 4 +, K +, Mg 2+ and Ca 2+) was carried out by using protonated tyramine (4-aminoethylphenol) as eluent ion. When using 1.2 m M tyramine–0.2 m M oxalic acid at pH 4.5 as eluent, incomplete separation of the monovalent cations and complete separation of the divalent cations were achieved in 17 min. Then, the addition of crown ethers in the eluent was carried out for the complete separation of the mono- and divalent cations. As a result, when using 1.2 m M tyramine–0.2 m M oxalic acid at pH 4.5 containing either 5 m M 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane) or 0.5 m M and 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) as eluent, excellently simultaneous separation of these cations was achieved in 21 min. The proposed IC–IPD was successfully applied to the determination of major cations in natural water samples.

Reactions of aromatic compounds with nucleophilic reagents in liquid ammonia: XVII. Effect of ionic association on the orientation in aryloxydefluorination of 2,4-difluoronitrobenzene

The analysis of dependence of fluorine replacement orientation in 2,4-difluoronitrobenzene effected by nucleophiles Y-C6H4OM (Y =p-OMe,p-Me,m-Me, H,p-F,p-Cl,m-F,m-Cl; M = Li, Na, K, Et4N, Bu4N) in liquid ammonia medium at -35‡C on the nature of M, Y, on nucleophile concentration, on addition of crown ethers, diaminoalkanes, and dimethoxyethane indicates the occurrence of ionic association at M = K, Na.

Dielectric studies of molecular mobility and microphase separation in segmented polyurethanes

This work deals with molecular mobility and microphase separation studies on segmented polyurethanes with different fragments, including crown ethers, as chain extenders and/or chain end groups. The techniques used include thermally stimulated depolarization current (TSDC) in the temperature range −185°–30°C and broadband dielectric relaxation spectroscopy (DRS) in the frequency and temperature ranges of 10 −2–10 6 Hz and −55°–80°C. The combination of these techniques allowed the secondary γ and β mechanisms, the primary α mechanism, the Maxwell–Wagner–Sillars (MWS) mechanism associated with interfacial polarization and dc conductivity σ dc to be recorded. The results suggest that addition of crown ethers promotes microphase separation. Specific characteristics of the primary α and the MWS relaxations and σ dc were found to systematically change with the degree of microphase separation. They should be further quantified and tested on selected systems.

Ion chromatographic separation of common mono- and divalent cations on an unmodified silica gel column by elution with oxalic acid containing crown ethers

An unmodified silica gel (Zorbax BP-SIL) column (150 × 4.6 mm id) was applied to ion chromatography (IC) with conductimetric detection of common mono- and divalent cations (Li+, Na+, NH4+, K+, Mg2+ and Ca2+). The retention behavior of these mono- and divalent cations on the column under acidic eluent conditions was investigated and it was found that the Zorbax BP-SIL behaved as a cation-exchange stationary phase under acidic eluent conditions and incomplete separation of these mono- and divalent cations was achieved. Therefore, the addition of crown ethers [1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5) and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6)] to the acidic eluent was carried out for the simultaneous separation of these mono- and divalent cations. Using 1.5 mmol dm–3 oxalic acid–3 mmol dm–3 15-crown-5 as the eluent, both highly sensitive detection and excellent simultaneous separation of these mono- and divalent cations were achieved in 10 min. The proposed IC method was successfully applied to the determination of major mono- and divalent cations in various natural water samples.

Crystal growth of zincophosphates from conventional media and reverse micelles: mechanistic implications

Zincophosphates can be synthesized with frameworks analogous to aluminosilicate zeolites. Previous studies have shown that reverse micelles, which are microdroplets of water dispersed in an oil-like medium, can serve as nucleation and growth centers for microporous materials. Zincophosphates with the sodalite framework can be readily made from reverse micelles, whereas the more open structure resembling the faujasite framework (ZnPO-X) could not be made. The concentration of sodium ions is found to play an important role in the nucleation of both sodalite and ZnPO-X. At increased sodium ion concentrations under conventional synthesis conditions, sodalite growth is favored. On the other hand, the addition of crown ethers and cryptands which complex sodium ions leads to growth of ZnPO-X. Based on these studies, we propose that the high sodium ion concentrations in reverse micelles cause the formation of sodalite. Infrared spectroscopic studies indicate that zinc- and phosphate-containing reverse micelles also contain significant amounts of disordered water, which can inhibit the nucleation of open-pore frameworks, such as ZnPO-X.

Simulation of change in conproportionation constants of the windmill complex [Cp3Co3(S6C6)]n− in the mixed-valence states (n = 1,2) by addition of crown ethers to solutions of alkaline metal ions

Counterion size effects on the conproportionation constants K c1 and K c2 of the windmill complex [Cp 3 Co 3 (S 6 C 6 )](1)(Cp = η 5 -C 5 H 5 ) in the mixed-valence states 1 − and 1 2− respectively have been investigated electrochemically in solutions of alkaline metal ions and crown ether. Addition of 18-crown-6 (18C6) or 15-crown-5 (15C5) to a solution of 1 in NaBPII 4 δ THF brings enormous increases in both K c1 and K c2 at a concentration similar to that of NaBP 4 , and the change of K c2 is more significant than that of K c1 . This behaviour can be simulated using the complexation constants of crown ether with a cation obtained by conductivity analysis and several equations concerning association, ion pairing equilibrium, conproportionation and charge balance assuming that most of 1 − , 1 2− and 1 3− exist in the form of ion pairs.

Effects of crown ethers and small amounts of cosolvent on the activity and enantioselectivity of α-chymotrypsin in organic sofvents

Abstract

Synthesis of (trichloromethyl)organosilanes by catalytic decarboxylation of (trichloroacetoxy)organosilanes

A method for preparing (trichloromethyl)organosilanes by the catalytic decarboxylation of the corresponding trichloroacetoxysilanes RMe2SiOC(O)CCl3 (R = Me, ClCH2, Ph, Me3Si, and H) has been developed. The method involves heating the starting compounds without a solvent in the presence of a catalyst (quaternary ammonium salts or potassium salts with the addition of crown ethers). Tertiary amines (Et3N, Bu3N) catalyze this reaction only when heating is carried out in donor aprotic solvents (THF, acetonitrile) in the presence of oxygen. Thermal decomposition of (trichloroacetoxy)organosilanes, in contrast to catalytic decarboxylation, begins at a higher temperature and yields a mixture of products.

Polylactones: 32. High-molecular-weight polylactides by ring-opening polymerization with dibutylmagnesium or butylmagnesium chloride

The dibutylmagnesium (Bu 2Mg)-initiated polymerizations of l-lactide at 120°C in bulk yielded poly( l-lactide) of low molecular weights ( η inh ⩽ 0.4 dlg −1 in CH 2Cl 2), regardless of reaction time and initiator concentration. Higher molecular weights were obtained in solution when carried out in the presence of ethers. The addition of crown ethers to polymerizations conducted in toluene at 0°C gave the best results, with η inh values up to 3.0 dlg −1 (in Ch 2Cl 2), corresponding to number-average molecular weights ( M ns) the order of 3 × 10 5g mol −1. These high-molecular-weight poly( l-lactide)s possess almost complete optical purity and show melting temperatures of ∼170°C. Relatively high-molecular-weight poly( d,l-lactide)s were also obtained by the Bu 2Mg-initiated polymerizations of racemic- or meso- d,d-lactides, with η inh values up to 1.4 dl g −1 (in CH 2Cl 2), corresponding to M n = 10 5, being found. The Grignard reagent, BuMgCl, gave somewhat better results than Bu 2Mg when used as an initiator for l-lactide in bulk. However, BuMgCl is not reactive enough to initiate satisfactory polymerizations in solution at temperatures ⩽25°C.