Crown Ether Units Research Articles

Calix[4]arenes Containing Urea and Crown/Urea Moieties: Effects of the Crown Ether Unit and Na+ Towards Anion Binding Ability.

Calix[4]arenes containing urea and crown/urea moieties, 7 and 10, respectively have been synthesized. 1H NMR titrations of 7 and 10 with anions in DMSO-d6 showed that 7 and 10 formed complexes with Cl−, Br−, NO3− and H2PO4− to a different extent. The association constants of 7 and 10 towards anions were calculated and found to vary as H2PO4−>Cl−>Br−>NO3−. However, compared to 7 the presence of the crown unit in 10 resulted in a slightly higher affinity to Cl− and Br−, but a lower affinity to H2PO4−. Upon addition of Na+, the binding ability of 10 towards H2PO4− is increased due to ion-pair enhancement.

Calix[4]arenes containing urea and crown/urea moieties: effects of the crown ether unit and Na + towards anion binding ability

Calix[4]arenes containing urea and crown/urea moieties, 7 and 10 , respectively have been synthesized. 1H NMR titrations of 7 and 10 with anions in DMSO- d 6 showed that 7 and 10 formed complexes with Cl −, Br −, NO 3 − and H 2PO 4 − to a different extent. The association constants of 7 and 10 towards anions were calculated and found to vary as H 2PO 4 −>Cl −>Br −>NO 3 −. However, compared to 7 the presence of the crown unit in 10 resulted in a slightly higher affinity to Cl − and Br −, but a lower affinity to H 2PO 4 −. Upon addition of Na +, the binding ability of 10 towards H 2PO 4 − is increased due to ion-pair enhancement.

Enantiomeric Separations in Capillary Electrochromatography with Crown Ether-Capped -Cyclodextrin-Bonded Silica Particles as Chiral Stationary Phase

Two novel types of crown ether capped β-cyclodextrin (β-CD) bonded silica, namely, 4′-aminobenzo-X-crown-Y (X=15, 18 and Y=5, 6, resp.) capped [3-(2-O-β-cyclodextrin)-2-hydroxypropoxy] propylsilyl-appended silica, have been prepared and used as stationary phases in capillary electrochromatography (CEC) to separate chiral compounds. The two stationary phases have a chiral selector with two recognition sites: crown ether and β-CD. They exhibit excellent enantioselectivity in CEC for a wide range of compounds. After inclusion of metal ions (Na+ or K+) from the running buffer into the crown ether units, the stationary phases become positively charged and can provide extra electrostatic interaction with ionizable solutes and enhance the dipolar interaction with polar neutral solutes. This enhances the host-guest interaction with the solute and improves chiral recognition and enantioselectivity. Due to the cooperation of the anchored β-CD and the crown ether, this kind of crown ether capped β-CD bonded phase shows better enantioselectivity than either β-CD- or crown ether bonded phases only. These new types of stationary phases have good potential for fast chiral separation with CEC.

Tuning the Charge-Separated Lifetimes of Ruthenium(II)polypyridyl-Viologen Dyads and Ruthenium(II)polypyridyl-Viologen Triads by the Formation of Supramolecular Assemblies with Crown Ethers

The synthesis and photophysical properties of a ruthenium dyad (4) and triad (5) are reported. Both biomimetic systems are physical models for the photosynthetic reaction center. They consist of a ruthenium(II)-polypyridyl sensitizer featuring chemically attached 3,3‘-dimethyl-4,4‘-viologen and 4,4‘-viologen electron acceptors. The binding of the chemically attached electron acceptors by the three structurally different crown ethers, DB30C10, BBO5O5, and AAO5O5, offers a remarkable tool for the enhancement of the lifetimes of the charge separated states (τCS), up to a factor of 2 × 104. The drastic increase in the lifetimes observed can be explained by a decrease in the reorganization energy λ due to the presence of the crown ether units bound to the viologen acceptor.

Copolymerization of 4′-vinylbenzo-15-crown-5 with Di(ethylene glycol) ethyl ether acrylate

Radical copolymerization behavior of 4′-vinylbenzo-15-crown-5, a vinyl monomer having apendant 15-membered crown ether unit (VCE) with di(ethylene glycol) ethyl ether acrylate (DEGEEA) was carried out in toluene solution using 2,2-azobisisobutyronitrile (AIBN) as an initiator. The copolymers were characterized by means of FT-IR,1H-NMR, and13C-NMR. The reactivity ratio of VCE and DEGEEA, determined by Fineman-Ross and Kelen-Tudos method, gave values 0.55 for VCE, and 0.11 for DEGEEA respectively.

Synthesis of 5‐vinyl‐m‐ phenylene‐m′‐phenylene‐32‐ crown‐10 and its radical polymerization behavior

AbstractSynthesis of a vinyl monomer, containing a 32‐membered crown ether unit (VCE) as a pendant group, was achieved by using tetra(ethylene glycol) dichloride, resorcinol, and 3,5‐dihydroxyacetophenone as starting materials. The product was identified by means of FTIR and 1H‐NMR. It was found that this monomer readily polymerizes by the conventional radical initiator 2,2′‐ azobisisobutyronitrile (AIBN) to afford a polymer whose number‐average molecular weight is 36 kg/mol; however, the final conversion of the polymer was < 80%. The results of the copolymerization of VCE with styrene (ST) or acrylonitrile (AN) are also discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2372–2379, 2002

PET fabric supported fixed site carrier membrane for selective metal ion transport

Development of a novel fixed site carrier membrane (FCM), supported by PET fabric for metal ion separation is reported. The membranes were prepared by dipping PET fabric into the methylene chloride solution of Poly(5-vinyl-m-phenylene-m′-phenylene-32-crown-10)_ (P(VCE)), a polymeric metal ion carrier. It was found that the flux of mono-valent metal ion transported across the membrane is significantly differed from each other and the flux decreases in the order Cs+>Rb+>K+>Na+>Li+ irrespective to the anion except perchlorate anion. It was explained in terms of the stability of the complex, formed by crown ether unit of the P(VCE) and the various metal ions, meanwhile, the lower rate of transport in the presence of perchlorate anion was ascribed to its low hydrophilicity.

Calix[4]arene-bis(dibenzocrown-6-ethers) with one proton-ionizable group

Two 1,3-alternate calix[4]arene-biscrowns with one proton-ionizable group and two dibenzocrown-6-ether units are synthesized. The compounds exhibit high Cs + extraction efficiency and selectivity. Cs +/Na + and Cs +/K + selectivities for the new N-(trifluoromethylsulfonyl)carbamoyl-substituted calix[4]arene-bis(dibenzocrown-6) are found to be higher than those for an analog with no benzo group substituents in the crown ether units.

OPTICAL LIMITING PROPERTIES OF OPTICALLY ACTIVE METAL-FREE AND METAL PHTHALOCYANINES SUBSTITUTED WITH CHIRAL BINAPHTHYL CROWN ETHER UNITS

The optical limiting properties of five optically active phthalocynines substituted with chiral binaphthyl crown ether units, (R)- and (S)- BNCE - H 2 Pc , (R)- and (S)-BNCE-CuPc, (S)-BNCE-PbPc, were investigated in solution at 532 nm with 10 ns pulses. The experimental results indicated that the (S)- and (R)-optical isomer exhibit similar optical limiting behavior and the central metal ions, Cu or Pb in the optically active metal phthalocyanine have not significantly enhanced the optical limiting behavior compared with that of the optically active metal-free phthalocyanine. In addition, the nonlinear absorption of the optically active metal-free and metal phthalocyanines was determined by the standard open aperture Z-scan technique.

Piezoelectric polymer with some optical characteristics

Limited information is available on the use of smart materials for smart optics technology, which requires the implementation of a material that combines both piezoelectric and optical characteristics. In this work an attempt was made to produce a flexible and transparent piezoelectric polymer. Network polymers with crown ether units were identified as prospective materials for this purpose. Experimental investigations on polyethylene glycol diepoxypropyl ether (PEGDE) were conducted by complexation with several inorganic salts under different heat treatment process and pressure conditions. An electronic circuit, which provides different ranges of electric fields, was developed to investigate the piezoelectric response of the synthesised polymer–salt complexes. A piezoelectric polymer was developed which showed a deformation of 0.78 mm, which is promising for focal length variation; however further work is needed to improve the transparency of the material.

Synthesis and properties of optically active 6,6′-didodecyl-1,1′-binaphthyl-phthalocyanine linked through crown ether units

A novel optically active 6,6′-didodecyl-1,1′-binaphthyl-metallophthalocyanine linked through crown ether units (( S)- Pc ) has been synthesized. A stable monolayer of ( S)- Pc that is able to bind metal ions can be formed at the air–water interface. Nonlinear absorption and optical limiting behavior of ( S)- Pc have also been observed.

New hybrid ditopic ligands containing fused phenanthroline and crown ether units

Reaction of 5,6-dihydroxy-1,10-phenanthroline with various poly(ethylene)glycol-ditosylates affords, in good yield, a series of ligands in which a phenanthroline binding site is attached to an adjacent crown ether unit; the NN chelating site may be coordinated to {Ru(bipy)2}2+ units to afford [Ru(bipy)3]2+ derivatives with pendant crown ether units, which can bind alkali metal ions.

Synthesis of optically active 1,1′-binaphthyl-phthalocyanines linked via a crown ether unit

Novel optically active metal and metal-free phthalocyanines, substituted with 1,1′-binaphthyl crown ether units, have been synthesized and characterized.

Effect of Alkali Metal Ion on the Ionic Conductivity of a Novel Liquid Crystal Containing a Dibenzo-18-Crown-6 Unit

Abstract A novel liquid crystal containing a dibenzo-18-crown-6 unit was prepared. The ionic conductivity was increased 1.5 orders of magnitude by the addition of an equimolar amount of K+. However neither Na+ nor Li+ yielded suitable samples corresponding to the ion-size matching of the crown ether unit.

Selective Potassium Ion Recognition by Benzo-15-crown-5 Fluoroionophore/γ-Cyclodextrin Complex Sensors in Water

Three fluoroionophores Cn (n = 1, 3, 5), in which the crown ether unit and pyrenyl moiety are connected by a -(CH2)n- spacer, have been used to construct supramolecular Cn/gamma-cyclodextrin (gamma-CyD) complexes for alkali metal ion sensing in water. The Cn (n = 3, 5) are found to selectively form 2:1 complexes with K+ in the presence of gamma-CyD and exhibit the pyrene dimer emission in water. Equilibrium analysis of the C3/gamma-CyD complex reveals that the observed dimer emission arises from a 2:1:1 complex of C3 with K+ and gamma-CyD. In the absence of K+, the fluorescence lifetimes for the dimer species ((C3)2CyD and (C3)2(CyD)2) and the monomer species (C3CyD and C3(CyD)2) are 13-18 and 130-180 ns, respectively. Upon addition of 0.10 M KCI, a rising component corresponding to pyrene excimer formation is observed at the dimer emission region. For the C3/gamma-CyD complex, the apparent association constant for K+ of (3.8 +/- 1.3) x 10(9) M(-2) is only slightly affected by the presence of Na+. Although the C5/gamma-CyD complex shows high sensitivity for K+, the selectivity for K+ over Na+ is lower than that of the C3/gamma-CyD complex. In contrast, fluoroionophore C1 with the shortest methylene spacer exhibits no response for alkali metal cations in the presence of gamma-CyD. These results demonstrate that the response function of supramolecular Cn/gamma-CyD complexes is strongly affected by the methylene spacer length of Cn. The highest K+ selectivity is obtained for the C3/gamma-CyD complexes in water.

Synthesis and cation complexation properties of crown ether polyamic acids/imides

The preparation and characterisation of the cation complexation properties of a series of polyamic acid and polyimides containing crown ether units are presented. It is found that the complexing power of the amic acid form of the polymers is significantly higher than that of the imide form; implying the ability of the carboxylic acid grouping to exhibit lariat behaviour. The carboxylic acid group enters into co-ordination with the cation, increasing the binding energy and hence the binding constant. Computer modelling has been used to provide insight into the various factors that influence the binding energy of the cation to the crown ether segment of the polymer chain. The complexation characteristics in aqueous and non-aqueous media are examined and the results are discussed in the context of changes in the contribution of the solvent to solvation sheath of the cation.

Kronenethersubstituierte 1,4-Distyrylbenzole und ihre Komplexierung mit Alkalipikraten

Crown Ether Substituted 1,4-Distyrylbenzenes and their Complexation with Alkali Picrates The 1,4-distyrylbenzenes 8 and 9, which contain two crown ether units, each, were prepared by Wittig—Horner reactions. Their complexation tendencies with alkali picrates (Li—Cs) in water/dichloromethane were investigated. Potas sium ions give the strongest complexes. Generally monomo-lecular 1:1-complexes are formed; however, [K-8] + [Pik]—, [K-9]+ [Pik]— and [Rb-8] + [Pik]— generate aggregates, for which a stairway structure is proposed.

Membranes Containing Oriented Supramolecular Transport Channels

The surface-induced alignment of crown ether units bearing amphiphiles into columnar structures within the pores of track-etched membranes is reported (see Figure). The ion-transport properties of these membranes are characterized by salt diffusion experiments. It is found that the membranes containing oriented supramolecular channels display strongly enhanced transport rates compared to those with non-oriented channels.

Redox Switchable Ionophores for Heavy and Transition Metal Cations

First examples of new, modular, redox switchable ionophores for heavy and transition metal cations are presented. These systems are based on a crown ether or polyethylene glycol unit substituted by the 1,2,4-thiadiazole/iminoylthiourea redox system (2a-4a, 2b-4b). The syntheses via a Boulton-Katritzki rearrangement are described and their cation selectivities, studied by extraction experiments, proved to be determined by the systems' redox state. Additionally, simple 5-anilino-3-phenyl-1,2,4-thiadiazole (5a) and the corre-sponding iminoylthiourea (5b), which do not contain a potential cation binding polyether substituent were also tested to investigate the complexation property of the redox active building block itself.

Cation recognition by self-assembled monolayers of oriented helical peptides having a crown ether unit.

Cation recognition of self-assembled monolayers (SAMs) of helical peptides having a crown ether unit was investigated by the impedance spectroscopy and cyclic voltammetry. Lipo-(Ala-Aib)8-Ala-Cr and Boc-Glu(Cr)-(Ala-Aib)8-Lipoa (Lipo, Lipoa, and Cr represent lipoic acid, lipoamide, and amidobenzo-18-crown-6, respectively) were synthesized and the helix SAMs were prepared. The peptides having a crown ether unit formed SAMs oriented nearly vertically to the substrate. The capacitance of the Lipo-(Ala-Aib)(8)-Ala-Cr SAM changed specifically with the addition of cations, and the binding constants of the SAM were larger than those of the crown ether in aqueous solution because of a large dipole moment of the helical peptide. In the case of the Boc-Glu(Cr)-(Ala-Aib)8-Lipoa SAM, the cation binding to the SAM showed a drastic decrease in the peak current of the cyclic voltammetry around 10(-5)M of K+ ion. In either capacitance measurement or cyclic voltammetry, the helical peptide SAM played an important role in the sensitive response to cations.