Applications of Macrocyclic Polyethers in Analytical Sensors and Ion Separation

Artificial macrocyclic polyethers were synthesized and applied as neutral carriers for ion-selective PVC membrane electrodes, ion-chromatographic packing materials, extractants and adsorbents for ion separation, coating materials for piezoeletrical membrane sensors for organic species, and ion-transport carriers through liquid membranes. Ion-selective electrodes such as those for K⁺ Na⁺, UO₂²⁺, Cs⁺, Pb²⁺, Fe³⁺, Hg²⁺ and Ag⁺ ions based on crown ether-phosphotungstic acid (PW) precipitates and dithio crown ethers respectively were prepared and showed good sensitivity and selectivity. Crown ether-PW precipitates were applied as adsorbents of rare-earth ions and some common heavy-metal ions. Some rare-earth ions were easily extracted with crown ethers, especially 15-crown-5. Poly(stytene/divinyl benzene) cryptand-22 resin was synthesized and applied as a bifunctional stationary phase of ion chromatography to separate bom cations and anions, even some organic carboxylate geometric isomers. Crown ethers such as mono-benzo-15-crown-5 was successfully applied as a coating material on piezoelectric quartz membrane sensors for some organic species. The oscillation frequency of the crown-ether quartz-membrane sensor was sensitive to organic vapours such as amines and alcohols. Upon adsorption of organic species on the crown-ether quartz membrane, the oscillation frequency of the sensor decreased obviously. Special crown ether such as dibenzo-16-crown-5-oxyacetic acid, decyl-cryptand-22 and 1, 4-dihydro-pyridine-18-crown-5 were synthesized and successfully applied as ion-transport carriers (ionophores) for transport of Na⁺ K⁺ and Mg²⁺ ions through liquid membranes.     

Synthesis and Complexation Behavior Studies of Novel Bis-crown Ethers

The novel unique structures of bis-crown ethers were successfully synthesized from tri (propylene glycol) di-acrylate with amino- and aza-crown ethers through Michael addition. The crown ethers contained the primary and the secondary amine group such as 2-aminomethyl crown ethers, 4-aminobenzo crown ethers and 1-aza crown ethers. The newly synthesized bis-crown ethers were characterized by elemental analyses, IR, ¹H NMR, ¹³C NMR, mass spectrum, respectively. The newly synthesized host compounds of bis-crown ethers showed complex ability with various sizes of alkali metal cations such as Na⁺, K⁺, Rb⁺ and Cs⁺. The complexation behavior was examined by ¹H NMR spectroscopy and UV spectrometry.     

Determination of orders of relative alkali metal ion affinities of crown ethers and acyclic analogs by the kinetic method

Ladders of relative alkali ion affinities of crown ethers and acyclic analogs were constructed by using the kinetic method. The adducts consisting of two different ethers bound by an alkali metal ion, (M₁ + Cat + M₂)⁺, were formed by using fast atom bombardment ionization to desorb the crown ethers and alkali metal ions, then collisionally activated to induce dissociation to (M₁ + Cat)⁺ and (M₂ + Cat)⁺ ions. Based on the relative abundances of the cationized ethers formed, orders of relative alkali ion affinities were assigned. The crown ethers showed higher affinities for specific sizes of metal ions, and this was attributed in part to the optimal spatial fit concept. Size selectivities were more pronounced for the smaller alkali metal ions such as Li⁺, Na⁺, and K⁺ than the larger ions such as Cs⁺ and Rb⁺. In general, the cyclic ethers exhibited greater alkali metal ion affinities than the corresponding acyclic analogs, although these effects were less dramatic as the size of the alkali metal ion increased.     

Adsorption of polymers with crown ether substituents on muscovite mica

Ultrahigh specific surface area muscovite with different ions at the surface (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ca²⁺, Sr²⁺, Ba²⁺, Cu²⁺) was treated with aqueous solutions of low molecular weight crown ethers and polymers with crown ether substituents. The adsorption was assessed by UV analysis of the supernatant solution, and with TGA and IR spectroscopy of the mica solids. In contrast to other layered silicates, the low molecular weight crown ethers show no affinity to any of the muscovite surfaces. The polymers can adsorb, however, depending on the type of surface cation. The results indicate that at least some of the crown ether moieties are complexed to surface cations and that the diameter of the ions at the surface plays an important role in the adsorption process.     

Selective complexation of alkali metal ions using crown ethers derived from calix[4]arenes: a computational investigation of the structural and energetic factors

A systematic analysis of the structural, energetic, and thermodynamic factors involved in alkali metal (i.e., Na⁺, K⁺, Rb⁺, and Cs⁺) complexation by four calix[4]arene crown-6 ethers in the 1,3-alternate conformation is presented here. The ligands (or hosts) in this work are identical to, or closely related to, the four molecules whose selectivity towards complexing Na⁺, K⁺, Rb⁺, and Cs⁺ from aqueous solutions was studied experimentally by Casnati et al. (Tetrahedron 60(36):7869–7876, 2004). By dividing the complexation process into three different contributions, namely, the binding energy of the ion to the crown, the elastic energy of the crown, and the solvation effect, it becomes clear that the primary factor that determines ion selectivity in crown-6-ethers is not the size of the crown, as currently believed. All four crown ethers preferentially complex with the smallest ion (Na⁺) in the gas phase. In the condensed phase, these crown-6 ethers preferentially complex with the larger ions only because the aqueous solvation energies of the alkali metal ions make it thermodynamically less favorable to extract the smaller ions from aqueous solutions. This suggests that the current understanding of the factors influencing the selectivity of metal ion complexation by crown ethers may be in need of revision.     

Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali Cations

A series of double-armed benzo-15-crown-5 lariats (3–8) have been synthesized by the reaction of 4′, 5′-bis(bromomethyl)-benzo-15-crown-5 (2) with 4-hydroxybenzaldehyde, phenol, 4-chlorophenol, 4-methoxyphenol, 2-hydroxybenzaldehyde, and 4-acetamidophenol in 43 ~ 82% yields, respectively. The complex stability constants (K _S) and thermodynamic parameters for the stoichiometric 1:1 and/or 1:2 complexes of benzo-15-crown-5 1 and double-armed crown ethers 3–8 with alkali cations (Na⁺, K⁺, Rb⁺) have been determined in methanol–water (V/V=8:2) at 25 °C by means of microcalorimetric titrations. As compared with the parent benzo-15-crown-5 1, double-armed crown ethers 3–8 show unremarkable changes in the complex stability constants upon complexation with Na⁺, but present significantly enhanced binding ability toward cations larger than the crown cavity by the secondly sandwich complexation. Thermodynamically, the sandwich complexations of crown ethers 3-8 with cations are mostly enthalpy-driven processes accompanied with a moderate entropy loss. The binding ability and selectivity of cations by the double-armed crown ethers are discussed from the viewpoints of the electron density, additional binding site, softness, spatial arrangement, and especially the cooperative binding of two crown ether molecules toward one metal ion.     

Synthesis and complexing properties of bis-crown ethers incorporating benzo-15-crown-5 and metallocene

Bis-crown ethers in which the benzo-15-crown-5 units were linked to 1,1′-positions of metallocene (M = Fe or Ru) with amide, ester, or ? C? C? bonds were synthesized. Complexing ability of the compounds with alkali, alkali earth, and transition metal cations were measured by the solvent extraction method. The results showed that these crown ethers had high affinity toward alkali metal cations (Li⁺, Na⁺, K⁺, and Rb⁺) and heavy-metal cations (Ag⁺ and Tl⁺). The difference of complexing ability for metal cations between ferrocene and ruthenocene derivatives could not be detected significantly. The extractability of metallocene-bis-crown ethers for metal cations was more larger than that of the corresponding mono-crown ethers, and irregular increments of extractability were explained by assuming the existence of a mixture of 1:1 and 2:1 complexes.     

Synthesis and Complexing Properties of <Emphasis Type="Italic">N,N</Emphasis>′-Bis(2-hydroxyethyl) Diaza Crown Ethers

The stability constants of complexes of 12-, 15-, and 18-membered diaza crown ethers, N,N′-dimethyl diaza crown ethers, and N,N′-bis(2-hydroxyethyl) diaza crown ethers with alkali and alkaline-earth metal ions in 95% aqueous methanol at 25°C were determined. The stability of the complexes of unsubstituted diaza crown ethers with alkali metal cations is low, probably because of stabilization of the exo,exo conformation of the ligands due to interaction of the nitrogen lone electron pairs with the solvent. The complexes with the double-charged cations are appreciably more stable. N,N′-Dimethyl diaza crown ethers form stable complexes with all the ions studied. As compared to the dimethyl derivatives, N,N′-bis(2-hydroxyethyl) diaza crown ethers form more stable complexes with the Na⁺, K⁺, Ca²⁺, Sr²⁺, and Ba²⁺ ions, which is due to participation of the side hydroxyethyl groups in the coordination.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 4, 2005, pp. 665–669.Original Russian Text Copyright © 2005 by Kulygina, Vetrogon, Basok, Luk’yanenko.     

Density Functional Theory Study of Selectivity of Crown Ethers to Li+ in Spent Lithium-Ion Batteries Leaching Solutions

It is a challenge to recover lithium from the leaching solution of spent lithium-ion batteries, and crown ethers are potential extractants due to their selectivity to alkali metal ions. The theoretical calculations for the selectivity of crown ethers with different structures to Li ions in aqueous solutions were carried out based on the density functional theory. The calculated results of geometries, binding energies, and thermodynamic parameters show that 15C5 has the strongest selectivity to Li ions in the three crown ethers of 12C4, 15C5, and 18C6. B15C5 has a smaller binding energy but more negative free energy than 15C5 when combined with Li⁺, leading to that the lithium ions in aqueous solutions will combine with B15C5 rather than 15C5. The exchange reactions between B15C5 and hydrated Li⁺, Co²⁺, and Ni²⁺ were analyzed and the results show that B15C5 is more likely to capture Li⁺ from the hydrated ions in an aqueous solution containing Li⁺, Co²⁺, and Ni²⁺. This study indicates that it is feasible to extract Li ions selectively using B15C5 as an extractant from the leaching solution of spent lithium-ion batteries.     

Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali Cations

A series of double-armed benzo-15-crown-5 lariats (3–8) have been synthesized by the reaction of 4′, 5′-bis(bromomethyl)-benzo-15-crown-5 (2) with 4-hydroxybenzaldehyde, phenol, 4-chlorophenol, 4-methoxyphenol, 2-hydroxybenzaldehyde, and 4-acetamidophenol in 43 ~ 82% yields, respectively. The complex stability constants (K _S) and thermodynamic parameters for the stoichiometric 1:1 and/or 1:2 complexes of benzo-15-crown-5 1 and double-armed crown ethers 3–8 with alkali cations (Na⁺, K⁺, Rb⁺) have been determined in methanol–water (V/V=8:2) at 25 °C by means of microcalorimetric titrations. As compared with the parent benzo-15-crown-5 1, double-armed crown ethers 3–8 show unremarkable changes in the complex stability constants upon complexation with Na⁺, but present significantly enhanced binding ability toward cations larger than the crown cavity by the secondly sandwich complexation. Thermodynamically, the sandwich complexations of crown ethers 3-8 with cations are mostly enthalpy-driven processes accompanied with a moderate entropy loss. The binding ability and selectivity of cations by the double-armed crown ethers are discussed from the viewpoints of the electron density, additional binding site, softness, spatial arrangement, and especially the cooperative binding of two crown ether molecules toward one metal ion.Graphical Abstract Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali CationsYU LIU*, JIAN-RONG HAN, ZHONG-YU DUAN and HENG-YI ZHANG This revised version was published online in July 2005 with a corrected issue number.     

Structural and Chemical Features of Extraction with Crown Ethers

Unlike linear extracting agents, in the extraction of metal salts from aqueous solutions of inorganic acids with crown ethers, the inclusion compounds, whose composition depends on several external and internal factors, go to the organic phase. The study of the molecular structure of the formed complexes by X-ray diffraction analysis showed that adducts of crown ethers with inorganic acids are host–guest complexes in which the hydroxonium ion is in the polyether macrocycle cavity. When the aqueous phase contains metal ions capable of displacing the hydroxonium ions from the macrocycle (K⁺, Pb²⁺, Hg²⁺, Sr²⁺, NH₄ ⁺), complexes containing metal cations as the guest in the macrocycle cavity, according to X-ray diffraction data, go to the organic phase. In addition, metals forming ionic associates (AuCl₄ ^-, FeCl₄ ^-, GaCl₄ ^-) in an aqueous solution are extracted with crown ethers in accordance with the anion-exchange mechanism. A system in which traces of metals in the 2 M HNO₃ +5 M HCl mixture serve as the aqueous phase was proposed for estimation of the general extraction ability of crown ethers. Such a system can be used for metal extraction via any possible mechanism. The stereochemical peculiarities of the extraction ability of crown ethers (compared to linear molecules) can be used for selective extraction and separation of metals.     

Absorption and fluorescence properties of acridinones,thioacridinones, aminoacridines and related crown ethers

We report a study on the absorptive and emissive properties of 9‐acridinones, 9‐thioacridinones and 9‐aminoacridines including six crown ether derivatives. The effect of solvents and of the addition of cations (Na⁺, K⁺, Ca2⁺ and Mg2⁺) on these properties has been studied. The absorption of the crown ether derivative of 9‐thioacridinone is sensitive to solvents while the fluorescence of crown ethers derived from 9‐aminoacridines shows some specificity towards cations. Empirical modeling was used to discuss the emission characteristics of these compounds.     

Cation-crown ether complex formation in water. II. Alkali and alkaline earth cations and 12-crown-4, 15-crown-5, and 18-crown-6

The stability constants and the partial molal volume and isentropic partial molal compressibility changes of complex formation between cations and crown ethers in water at 25°C are presented. The cations involved are Na⁺, K⁺, Rb⁺, Cs⁺, Ca²⁺, and Ba²⁺, and the crown ethers are 12-crown-4, 15-crown-5, and 18-crown-6. Values of V of complex formation have been discussed in terms of two simple models, one based on the scaled particle theory, and the others on the Drude-Nernst continuum model. The results indicate that the charge of the potassium cation in 18-crown-6 is especially well screened from the water. On this basis hydration numbers of complexed cations have been calculated. This shows that the size of the cation compared to the crown ether hole is important for the contacts between complexed cations and water.     

Natural Abundance 17O-NMR. Study of Some Macrocyclic Complexes with Alkali Metal Cations

Complexation between crown ethers 12C4, 15C5, 18C6 and cryptand 222, and alkali cations Li⁺, Na⁺, K⁺ in various solvents were studied by ¹⁷O-NMR. spectroscopy. Small diamagnetic shifts arising from the cation electric field are observed. They increase according to the sequence K⁺ < Na⁺ < Li⁺. ¹⁷O-linewidth are discussed and compared to the ¹³C relaxation times. Linewidth modification results mainly from modifications of the effective correlation time. In general, for crown ethers, considerable line broadening occurs when the cation fits well into the cavity but line narrowing occurs when the cation is much smaller than the cavity.     

Fine‐tuning of electromembrane extraction selectivity using 18‐crown‐6 ethers as supported liquid membrane modifiers

Selectivity of electromembrane extractions (EMEs) was fine‐tuned by modifications of supported liquid membrane (SLM) composition using additions of various 18‐crown‐6 ethers into 1‐ethyl‐2‐nitrobenzene. Gradually increased transfer of K⁺, the cation that perfectly fits the cavity of 18‐crown‐6 ethers, was observed for EMEs across SLMs modified with increasing concentrations of 18‐crown‐6 ethers. A SLM containing 1% w/v of dibenzo‐18‐crown‐6 in 1‐ethyl‐2‐nitrobenzene exhibited excellent selectivity for EMEs of K⁺. The established host–guest interactions between crown ether cavities in the SLM and potassium ions in donor solution ensured their almost exhaustive transfer into acceptor solution (extraction recovery ～92%) within 30 min of EME at 50 V. Other inorganic cations were not transferred across the SLM (Ca²⁺ and Mg²⁺) or were transferred negligibly (NH₄⁺, Na⁺; extraction recovery < 2%) and had only subtle effect on EMEs of K⁺. The high selectivity of the tailor‐made SLM holds a great promise for future applications in EMEs since the range of similar selective modifiers is very broad and may be applied in various fields of analytical chemistry.     

Ion formation in fast atom bombardment mass spectrometry: a divided probe investigation of gas-phase reactions

Some ion-formation processes during fast atom bombardment (FAB) are discussed, especially the possibility of reactions in the gas phase. Divided (two halves) FAB probe tips were used for introducing two different samples into the source at the same time. Our results showed [M + A]⁺ ions (where M = crown ethers and A = alkali metal ions), can be produced, at least in part, in the gas phase when crown ethers and sources of alkali metal ion are placed on two halves of the FAB probe tip. The extent of this ion formation depends on the volatility of the crown ether and on steric factors. Cluster ions such as (M + LiCl)Li⁺, (2M + LiCl)Li⁺, [2M + K]⁺ and [2M + Na]⁺ are also observed to form in the gas phase. Unimolecular decompositions contribute to some ions detected in FAB. When the alkali ion salt and the crown ether are mixed together the probability of [M + A]⁺ ion formation increases significantly, regardless of the volatility of the crown ether.     

Separation of common monovalent and divalent cations by ion chromatography on calcined silica gel cation-exchange stationary phases, with tyramine-oxalic acid-containing crown ether mobile phases and indirect photometric detection

Summary Pure silica gels (Pia Seed 5S-60-SIL) calcined at 200, 400, 600, 800 and 1000°C for 5 h have been used as cation-exchange stationary phases in ion chromatography with indirect photometric detection for common monovalent and divalent cations (Li⁺, Na⁺, NH₄ ⁺, K⁺, Mg²⁺ and Ca²⁺); 0.75mm tyramine (4-(2-aminoethyl)phenol)-0.25mm oxalic acid, pH 5.0, containing crown ethers (18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane) or 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)) was used as mobile phase. With increasing calcination temperature, the amounts of the crown ethers adsorbed on the calcined silica gel column increased and, consequently, the effect of the crown ethers as retention modifiers for these cations increased. Excellent simultaneous separation and highly sensitive detection of these cations at 275 nm were achieved in 17 min by use of a 150 mm×4.6 mm i.d. column packed with silica gel calcined at 1000°C and use of 0.75mm tyramine-0.25mm oxalic acid, pH 5.0, containing either 0.5mm 18-crown-6 or 5.0mm 15-crown-5 as mobile phase.     

The synthesis of novel crown ethers,part X, 4‐propyl‐and 3‐ethyl‐4‐methylchromenone‐crown ethers

Starting from ethyl propionylacetate, and ethyl 2‐ethylacetoacetate we prepared 4‐propyl‐7,8‐, 4‐propyl‐6,7‐, 3‐ethyl‐4‐methyl‐7,8‐ and 3‐ethyl‐4‐methyl‐6,7‐dihydroxy‐2H‐chromenones which were allowed to react with the bis‐dihalides or ditosylates of glycols in DMF/Na₂CO₃ to afford the 6,7‐ and 7,8‐chromenone derivatives of 12‐crown‐4, 15‐crown‐4 and 18‐crown‐6. The products were identified using ir, ¹³C and ¹H nmr, ms and high resolution mass spectroscopy. The cation selectivities of chromenone crown ethers with Li⁺, Na⁺ and K⁺ cations were estimated from the steady state emission fluorescence spectra of free and cation complexed chromenone macrocyclic ethers in acetonitrile.     

Factors Influence Complexing Selectivity of Lariat Crown Ethers Toward Alkali Metal Ions in Electrospray Ionization Mass Spectrometry

The selectivity of eight lariat crown ethers in the sym‐dibenzo‐16‐crown‐5 series toward alkali metal ions was studied with electrospray ionization mass spectrometry under different conditions. With the exception of 2g , which is equally selective toward Na⁺ and Li⁺, all other lariat crown ethers show the best selectivity toward Li⁺ in methanol. Factors that influence the selectivity include the water content, counterions, nature of the side arms, and the externally added cations. Iodide gives the best Na⁺ selectivity with R_I > R_Br > R_Cl. Increased water content profoundly increases the Na⁺ selectivity when the side arm is hydrophilic and the steric hindrance is small. Externally added cations (Cs⁺ and/or Rb⁺) enhance the Na⁺ selectivity by exchanging the smaller Li⁺ from the cavity.     

Ion–molecule reactions between organometallic ions and crown ethers in the gas phase

Ion–molecule reactions of the metal-containing ions LM⁺ (L = (acac)₂, acac, C₆H₆, C₅H₅; M = In, Ga, Co, Fe, Ni, Cr, Mn, Pd, Rh, Tl, La, Pr, Yb, Nd) with crown ethers in the gas phase were studied. Two major reactions were observed: adduct formation and substitution of a metal atom ligand by a crown ether. The relative abundances of the two reactions depends on the ease with which the metal atom may be reduced. Ligand substitution can involve hydrogen rearrangements with loss of acetylacetone or cyclopentadiene for crown ethers having mobile H atom(s). The use of ion–molecule reactions in the structural characterization of crown ethers and transition metalcontaining ions is discussed.