Crown Ether Cavity Research Articles

Alkali metal cation complexation by 1,3-alternate, mono-ionisable calix[4]arene-benzocrown-6 compounds

Alkali metal cation extraction behaviour for two series of 1,3-alternate, mono-ionisable calix[4]arene-benzocrown-6 compounds is examined. In Series 1, the proton-ionisable group (PIG) is a substituent on the benzo group of the polyether ring that directs it away from the crown ether cavity. In Series 2, the PIG is attached to one para position in the calixarene framework, thereby positioning it over the crown ether ring. Competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform shows high Cs+ efficiency and selectivity. Single-species extraction pH profiles of Cs+ for Series 1 and 2 ligands with the same PIG are very similar. Thus, association of Cs+ with the calixcrown ring is more important than the position of the PIG relative to the crown ether cavity. Solid-state structures of two unionised ligands from Series 2 are presented. Also described is a crystal containing two different ionised ligand–Cs+ complexes.

Thermodynamics of alkali metal cation complexation by ionised calixcrown ligands

Binding of alkali metal cations (AMCs) by 1,3-alternate, ionised calix[4]arene-benzocrown-6 ligands was investigated by isothermal calorimetric titration in methanol. The groups of –C(O)NHSO2CH3 and more acidic –C(O)NHSO2CF3 were attached to the 1,3-alternate calix[4]arene-benzocrown-6 skeleton in two locations. In one series, the acidic group was attached to the para position of one aromatic ring in the calixarene framework, thereby positioning it over the polyether cavity. In the other series, the ionisable group was a substituent on the benzo group in the polyether ring. This oriented the acidic group away from the crown ether cavity. For these calixcrown ligands, the effects of the location of the ionisable group and its acidity and the identity of the AMC on the binding constant, enthalpy and entropy of complexation are assessed.

Development of Chemically Bonded Crown Ether Stationary Phases in Capillary Ion Chromatography

Three types of crown ethers (i.e. 1-aza-15-crown-5-ether, 1-aza-18-crown-6-ether and 2-aminomethyl-18-crown-6-ether) were chemically bonded to silica gels via a simple 2-step reaction and the resulted stationary phases were evaluated for the separation of both anions and cations in capillary ion chromatography. It was found that the chemically bonded stationary phases were most stable and relatively sharper peaks were obtained when a mixture of toluene:acetonitrile = 7:3 was used as the reaction solvent in the second step reaction. The size of crown ether cavity as well as the presence of nitrogen atom within the cavity affected the retention behaviors of the ions. As for the separation of anions, it was found that the eluent cations were trapped on the stationary phases and acted as the anion-exchange site, viz. the anions were separated in the ion-exchange mode. Without the obstruction of nitrogen atom, 2-aminomethyl-18-crown-6-ether could easily form complexes with metal cations, and the retention as well as elution order were dependant on the complex formation constant between crown ether and the metal cations. Eluent with higher pH favored the retention and separation of the metal cations.

Lipophilic, Mono-ionizable, Calix[4]arene-bis(benzocrown-6) Compounds for Solvent Extraction of Cesium from Nuclear Wastes: Synthesis and Evaluation

As potential radiocesium extractants from nuclear waste solutions, a series of lipophilic, proton-ionizable calix[4]arene-bis(benzocrown-6) compounds with their calixarene units locked in the 1,3-alternate conformation was prepared. In these ligands, the acidic side arm is positioned over one crown ether cavity to enhance metal ion extraction. Upon ionization of the acidic group, the ligand provides the requisite anion for electroneutral extraction complex formation. To enhance the lipophilicity of the extractants, a 2-ethylhexyl group was attached to the benzo group of each crown ether fragment. Using radiotracer techniques and ICAP spectrometry, the ligands were evaluated in terms of the efficiency and selectivity with which they extract Cs+ from aqueous solutions into chloroform.

Synthesis and application of novel magnetite nanoparticle based azacrown ether for protein recognition

This article is the first report showing the human serum albumin (HSA) binding studies by using a new magnetite nanoparticle containing azacrown ether moieties via solid-liquid extraction process. The structure of the newly prepared magnetite nanoparticle was clarified by using attenuated total reflectance (ATR) infrared spectro- scopy, scanning electron microscopy (SEM), UV-vis and elemental analysis. Analytic results indicated that modifi- cation of the surface of the magnetite nanoparticles with azacrown ether derivative was successfully carried out. The protein binding studies exhibited that the modified magnetite nanoparticles could be efficiently used for the binding of the human serum albumin (HSA) in aqueous solutions via non-covalent interaction between crown ether cavity and amino group of the protein.

ChemInform Abstract: Crown and Lariat Ethers

AbstractReview: 103 refs.

Electrochemical investigation of nano-baskets of calix[4]-1,3-crowns-5,6 complexes

Four nano-baskets of calixarene including cone 25,27-di(carboxymethoxy)calix[4]arene-crown-5, 1,3-alternate 25,27-di[carboxymethoxy]-calix[4]arene-crown-5, cone 25,27-bis[carboxymethoxy]calix[4]arene-crown-6 and 1,3-alternate 25,27-di[carboxymethoxy]-calix[4]arene-crown-6 were synthesized and their binding abilities towards alkali and alkaline earth metals as well as some lanthanides were studied using differential pulse voltammetry. The novelty of this study was investigation of those macrocyclic complexes by voltammetric behaviors of two acidic moieties in each scaffold during complexation of crown ether ring. Their voltammetric behaviors were closely related to the complex formation by entrapment of cation into crown ether cavity and ion–dipole interaction between cation and acidic moieties in calixcrowns. The results revealed the selective changes in voltammetric behavior of synthesized scaffolds toward the cations. Moreover, the position of crown ether in 1,3-alternate instead of cone enhanced the domain of binding ability to more cations. Furthermore, it was shown that those carboxylic acid moieties, which were far from the crown ether ring in the 1,3-alternate, did not affected by encapsulated cations in the coordination space of crown ether and showed no voltammetric behavior.

Voltammetric Study of Nano-baskets of Calix[4]-1,3-crowns-5, -crowns-6 Complexes

Four nano-baskets of calixarene including di(carboxymethoxy)calix[4]arene-crown-5 and -crown-6 in both cone and 1,3-alternate conformations, were synthesized and their binding abilities towards alkali and alkaline earth metals and some lanthanides were studied using differential pulse voltammetry. The novelty of this study is investigation of calixarene complexes by voltammetric behaviors of two acidic moieties during complexation with crown ether ring. Their voltammetric behaviors not only were related to complex formation (by entrapment of cation into crown ether cavity) but also were controlled by ion–dipole interaction between cation and carboxylic acid moieties. The results revealed the selective changes in voltammetric behavior of synthesized scaffolds toward cations. Moreover, the position of crown ether in 1,3-alternate conformations enhanced the domain of binding ability to more cations. Furthermore, carboxylic acid moieties, which were far from the crown ether ring in 1,3-alternate, were not affected by encapsulated cations in the coordination space of crown ether and hence, they showed no voltammetric behavior.

Response of Crown Ether Functionalized Polythiophenes to Alkaline Ions

The sensing response of 15-crown-5-ether functionalized polythiophene to Li+, Na+, and K+ has been investigated at the atomistic level using molecular dynamics simulations. The stability associated with all the identified binding sites has been corroborated by quantum mechanical calculations. Although the cavity of the macrocycle is not the most visited binding site, such receptor is responsible of the selective sensing response of this polythiophene derivative. PF6(-) counterions reduce the mobility of the alkaline cations, which do not occupy the crown ether cavity of consecutive repeating units due to electrostatic repulsions. Furthermore, the relative entropy for the “free state → bound state” has been estimated using a procedure based on the covariance matrix atom-positional fluctuations. Evaluation of the entropic contributions allow us to complete the thermodynamics scenario of binding process, which was recently initiated by calculating the enthalpies at quantum mechanical level [ Chem. Eur. J. 2009, 15, 4676]. Results indicate an entropycally driven binding preference.

Mono- and ditopic models of binding of a photochromic chromene annelated with an 18-crown-6ether with protonated amino acids

In this work, the interaction of protonated amino acids with a chromene bearing a fused 18-crown-6 ether moiety was studied by UV-vis and NMR spectroscopy. Initial closed forms of the chromene form monotopic 1 : 1 complexes, the ammonium group being localized inside the crown ether cavity. UV-irradiation leads to transformation of the ring-closed species into the ring-opened form. Depending on the amino acid length, either ditopic or monotopic 1 : 1 complexes are formed. Such complexes are stabilized by the additional H-bonding between the carboxylic group of the acid and the carbonyl oxygen atom of the ring-opened form. Cessation of the irradiation results in ring-closure to the chromene with concomitant change of the complexation mode.

Binding Study of Ionizable Calix[4]-1,3-Crowns-5,6 Nano-baskets by Differential Pulse Voltammetry

Four proton di-ionizable diacid conformers of cone 25,27-di(carboxymethoxy)calix[4]arene-crown-5, 1,3-alternate 25,27-di[carboxymethoxy]-calix[4]arene-crown-5, cone 25,27-bis[carboxymethoxy]calix[4]arene-crown-6 and 1,3-alternate 25,27-di[carboxymethoxy]-calix[4]arene-crown-6 were synthesized and their binding abilities toward alkali and alkaline earth metals as well as some lanthanides were studied by means of differential pulse voltammetry. The novelty of this study was investigation of those nano-baskets by voltammetric behavior of two acidic moieties in each scaffold during complexation of the crown ether ring. Their voltammetric behavior was closely related to the complex formation by entrapment of the cation into the crown ether cavity and ion-dipole interaction between cation and acidic moieties in calixcrowns. The results revealed the selective changes in voltammetric behavior of synthesized scaffolds toward the cations. Moreover, the position of crown ether in 1,3-alternate instead of cone enhanced the domain of binding ability to more cations. Furthermore, it was shown that those carboxylic acid moieties, which were far from the crown ether ring in the 1,3-alternate, were not affected by encapsulated cations in the coordination space of crown ether and showed no voltammetric response.

Binding Survey of Ionizable Calix[4]‐1,2‐crown‐3 Nano‐baskets by Differential Pulse Voltammetry

AbstractThree nano‐baskets of p‐tert‐butylcalix[4]arene‐1,2‐crown‐3 were synthesized and their binding abilities towards alkali and alkaline earth metals as well as some lanthanides were studied using differential pulse voltammetry. The novelty of this study was the investigation of macrocyclic complexes by voltammetric behaviors of two acidic moieties in each scaffold. Their voltammetric behaviors were closely related to the complex formation by entrapment of cation into crown ether cavity and ion‐dipole interaction between cation and acidic moieties in calixcrowns. The results revealed that the sulfur atom in the crown ring as well as the position of crown‐3 ether in 1,2‐alternate instead of cone conformer changed the binding ability of the scaffold to more cations.

Intraparticle Charge Delocalization of Carbene-Functionalized Ruthenium Nanoparticles Manipulated by Selective Ion Binding

Olefin metathesis reactions of carbene-stabilized ruthenium nanoparticles were exploited for the incorporation of multiple functional moieties onto the nanoparticle surface. When the nanoparticles were cofunctionalized with 4-vinylbenzo-18-crown-6 and 1-vinylpyrene, the resulting particles exhibited fluorescence characteristics that were consistent with dimeric pyrene with a conjugated chemical bridge, with three peaks observed in the emission spectra at 391, 410, and 485 nm. The behaviors were ascribed to intraparticle charge delocalization between the pyrene moieties afforded by the conjugated Ru═carbene interfacial linkages. Notably, upon the binding of metal ions in the crown ether cavity, the emission intensity of the nanoparticle fluorescence was found to diminish at 485 nm and concurrently increase at 391 and 410 nm rather markedly, with the most significant effects observed with K(+). This was accounted for by the selective binding of 18-crown-6 to potassium ions, where the positively charged ions led to the polarization of the nanoparticle core electrons that was facililated by the conjugated linkage to the metal surface and hence impeded intraparticle charge delocalization. Control experiments with a pyrene-crown ether conjugate (2) and with ruthenium nanoparticles cofunctionalized with 4-vinylbenzo-18-crown-6 and 1-allylpyrene suggested that the through-bond pathway played a predominant role in the manipulation of intraparticle electronic communication whereas the contributions from simple electrostatic interactions (i.e., through-space pathway) were minimal.

Crown Ether Cavity-Containing Copolymers via Controlled Alternating Cyclocopolymerization

The cyclocopolymerization of difunctional styrenic flexible monomers with maleic anhydride via reversible addition–fragmentation chain transfer (RAFT) has been investigated. The reaction proceeded to yield gel-free copolymers soluble in organic solvents. The kinetic study indicated that the cyclocopolymerization of difunctional styrenic flexible monomer with maleic anhydride proceeded in a controlled manner. The structures of resulting crown ether cavity-containing copolymers were characterized by the use of NMR spectroscopy and MALDI-TOF mass spectrometry. The crown ether cavities in copolymers exhibited a selective recognition for certain dialkylammonium ions.

Controlled self-assembly of bis(crown)stilbenes into unusual bis-sandwich complexes: structure and stereoselective [2+2] photocycloaddition

It was shown by 1H NMR spectroscopy that symmetrical bis(crown)stilbenes (L) and small alkali and alkaline-earth metal cations form 1(L) ∶ 1(Mm+) and 1(L) ∶ 2(Mm+) complexes in MeCN solutions. In the case of large or hydrated metal cations such as Cs+, Rb+, K+, Ba2+, Sr2+, [Ca(H2O)x]2+ and stilbenes with a small crown-ether cavity as compared with the metal cation size, stable bis-sandwich complexes 2(L) ∶ 2(Mm+) can also be formed. A stable bis-pseudosandwich 2 ∶ 2 complex is also produced from bis(18-crown-6)stilbene with the propanediammonium ion. The effect of the crown-ether size and the cation size and nature on the route of stilbene phototransformation and product composition was elucidated. The bis-(pseudo)sandwich complexes undergo effective stereoselective [2+2] photocycloaddition giving mainly rctt isomers of new 1,2,3,4-tetracrown cyclobutanes. The structures of complexes of bis(crown)stilbenes and obtained cyclobutanes were confirmed by X-ray diffraction.

Lower-rim versus upper-rim functionalization in di-ionizable calix[4]arene-crown-5 isomers. Synthesis and divalent metal ion extraction

Two series of di-ionizable calix[4]arene-crown-5 isomers in the cone conformation are synthesized to probe the effect of the pendant acidic group location on their metal ion extraction properties. In one series, the ionizable groups are attached to the lower rim of the calix[4]arene scaffold, which orients them near the crown ether cavity. In the second series, the ionizable groups are connected to the upper rim positioning them away from the crown ether ring, but close to the hydrophobic pocket of the calix[4]arene unit. The metal ion extraction behaviors of the two series of ligands are compared in extractions of alkaline earth metal cations, Hg 2+, and Pb 2+.

MOLECULAR MODELLING OF Mn<sup>+</sup>.[DBz16C5] COMPLEXES, M = Li<sup>+</sup>, Na<sup>+</sup> AND Zn<sup>2+</sup> BASED ON MNDO/d SEMIEMPIRICAL METHOD

The effect of substituent on dibenzo-16-crown-5 (DBz16C5) and interaction between these crown ether with metal cations was evaluated using computational chemistry calculations. Substituens where are connected to the benzene ring on the DBz16C5 are -COOH, -Br, -COOC2H5, -CHO, -CH=CHCO2H, -CH=CHCO2C2H5 and -CH(OH)CH3. The analysis based on computational chemistry calculation using MNDO/d semi empirical method was done. The first step is structure optimization of crown ether followed by optimization of crown ether-metals cation complexes Mn+.[DBz16C5], where M is Li+, Na+ and Zn2+. Interactions of the crown ether and cation were discussed in term of the structure parameter of crown ether, atomic charges and energy interaction of the crown ether-metals cation. Electron donating groups increase the capability of crown ether to bind cation by means of induction effect, while electron withdrawing groups reduce the ability of crown ether to bind cation. Any substituent on the benzene in DBz16C5 which can be make the symmetrical form of the crown ether-metals cation complexes will increase the selectivity of the crown ether to bind the cation. Selectivity of the crown ether to bind cation also depends on the compatibility of the diameter of cation and cavity of crown ether. DBz16C5 has higher selectivity to bind the Na+ compare to the Li+ and Zn2+. Keywords: selectivity, dibenzo-16-crown-5, MNDO/d

Supramolecular Architectures from Ammonium-Crown Ether Inclusion Complexes in Polyoxometalate Association: Synthesis, Structure, and Spectroscopy

The tetrahedral (Td) molecular cation ammonium ion (NH4+) gets incorporated with the smaller-cavity crown ethers through three N+−H···O hydrogen bonding interactions, while the fourth N−H bond is projected outward from the crown ether cavity. A hydrogen bonding acceptor, such as a polyoxometalate anion, if placed in suitable position in the crystal lattice, can interact with the ammonium-crown ether supramolecular complex involving the fourth N−H bond donation. This article describes supramolecular association of ammonium-crown ether host−guest complexes with polyoxometalate anions in five crystalline solids, formulated as [NH4(B18C6)][Bu4N][Mo6O19] (1), [NH4(B18C6)]4[SiW12O40]·2CH3CN (2), [NH4(DB18C6)]2[Mo6O19]·4H2O (3), [NH4(DC18C6)]2[Mo6O19] (4), and [NH4(DB30C10)]2[Mo6O19]·CH3COOH (5), where B18C6 = benzo-18-crown-6, DB18C6 = dibenzo-18-crown-6, DC18C6 = dicyclohexyl-18-crown-6, and DB30C10 = dibenzo-30-crown-10. Single crystal X-ray structural investigations on these solids confer P1̅ space symmetry (No. 2) for the compounds 1−2; C2/c space symmetry (No. 15) for the compound 3; P21/n space symmetry (No. 14) for the compound 4, and C2/m (No. 12) space symmetry for the compound 5. Careful examination of the supramolecular interactions between the different molecular fragments show direct contact between the ammonium cation and the polyoxometalate anion (N+−H···O) in the crystal structure of the compounds 1, 2, and 4. Lattice water molecules have taken the role of hydrogen bonding acceptor (N+−H···O) in the crystal structure of compound 3, while the larger and flexible crown ether DB30C10 has wrapped around the ammonium cation in the case of compound 5. Thus, there is no direct supramolecular interaction between the ammonium cation and the polyoxometalate anion (N+−H···O) in the crystal structures of compounds 3 and 5, where the ammonium−crown ether cations are associated with the polyoxometalate anions only via C−H···O hydrogen bonding interactions. Detailed spectroscopic (IR, 1H NMR, and UV−visible) analyses have been included in comprehending the supramolecular association between the inclusion complexes and polyoxometalate anions. The X-ray powder diffraction analyses have been performed to scrutinize the phase purity of the solids.

INTERACTION BETWEEN Li<sup>+</sup> CATION WITH CROWN ETHERS OF Bz15C5, DBz16C5 AND DBz18C6: MOLECULAR MODELING BASE ON MNDO/d SEMIEMPIRICAL METHOD

The aim of this research is to find information about the substituent effect to the structure of crown ether benzo-15-crown-5 (Bz15C5), dibenzo-16-crown-5 (DBz16C5) and dibenzo-18-crown-6 (DBz18C6), and also crown ether selectivity to coordinate a Li+ metal cation. The presence of substituent could change the conformations flexibility of crown ether during interact with metal cation. In this research semi empirical MNDO/d method was used for calculations. Firstly, geometry optimization was conducted to crown ethers structure using MNDO/d methods. The next steps were running the geometry optimization of complexes between cation Li+ with crown ethers. Data were produced from these calculation are the parameter of crown ether structures, structures of the complexes, and the binding energy of the cation-crown ethers. The presence of electron-withdrawing substituents decreased the binding energy while that of electron-donating one increase the binding energy (value of ΔE more negative). The substituents which are increase the degree of symmetry of the cation-crown ether complexes could give the increase of crown ether selectivity to bind the cation. Selectivity of crown ether to bind the cation depends on the structural match between ionic radii of crown ether cavity (the ion-cavity size concept). Bz15C5 what has higher selectivity to bind Li+ than DBz16C5 and DBz18C6. Keywords: selectivity, crown ether, MNDO/d.

The First Examples of a Crown Ether Intramolecularly Encapsulating Mono- and Diorganotin Dications: Synthesis and Structures of [PhSnCH2([16]crown-5)][ClO4]2and [HOSnCH2([16]crown-5)][Y]2(Y=ClO4, CF3SO3)

The reaction of silver perchlorate with [PhI(2)SnCH(2)([16]crown-5)] (1) and [I(3)SnCH(2)([16]crown-5)] (2) gave the organotin(IV)-substituted crown ether complexes [PhSnCH(2)([16]crown-5)][ClO(4)](2) (3) and [HOSnCH(2)([16]crown-5)][Y](2) (4: Y=ClO(4), 5: Y=CF(3)SO(3)), respectively. All compounds have been isolated as air-stable materials and characterised by (1)H, (13)C, (119)Sn and (119)Sn MAS (5) NMR spectroscopy, ESIMS spectrometry, elemental analysis and by single-crystal X-ray diffraction analysis. The molecular structures of 3-5 show that the tin(IV) cation fits perfectly into the crown ether cavity and is coordinated by the five oxygen atoms of the ring to give a pentagonal bipyramidal configuration about the central metal cation. Notably, compounds 4 and 5 contain the first monomeric monoorganotin dication. Moreover, there are (3)J((1)H,(119)Sn) coupling constants to the CH(2)CH proton of 377 (3) and 470 Hz (4, 5) that are, to the best of our knowledge, the biggest such couplings ever reported.