Crown Ether Moiety Research Articles

Controlled Interconversion of Superposed-Bistriangle, Octahedron, and Cuboctahedron Cages Constructed Using a Single, Terpyridinyl-Based Polyligand and Zn(2.).

Metallomacromolecular architectural conversion is expanded by the characterization of three different structures. A quantitative, single-step, self-assembly of a shape-persistent monomer, containing a flexible crown ether moiety, gives an initial Archimedean-based cuboctahedron that has been unequivocally characterized by 1D and 2D NMR spectroscopy, mass spectrometry, and collision cross section analysis. Both dilution and exchange of counterions, transforms this cuboctahedron into two identical octahedrons, which upon further dilution convert into four, superposed, bistrianglar complexes; increasing the concentration reverses the process. Ion binding studies using the cuboctahedral cage were undertaken.

Engineering Functionalization in a Supramolecular Polymer: Hierarchical Self-Organization of Triply Orthogonal Non-covalent Interactions on a Supramolecular Coordination Complex Platform.

Here we present a method for the construction of functionalizable supramolecular polymers by controlling three orthogonal interactions within a single system: (i) coordination-driven self-assembly; (ii) H-bonding; and (iii) host-guest interactions between crown ether and dialkylammonium substrates. Three unique molecules constitute the supramolecular construct, including a 2-ureido-4-pyrimidinone (UPy)-functionalized rigid dipyridyl donor and a complementary organoplatinum(II) acceptor decorated with a crown ether moiety that provide the basis for self-assembly and polymerization. The final host-guest interaction is demonstrated by using one of two dialkylammonium molecules containing fluorophores that bind to the benzo-21-crown-7 (B21C7) groups of the acceptors, providing a spectroscopic handle to evaluate the functionalization. An initial coordination-driven self-assembly yields hexagonal metallacycles with alternating UPy and B21C7 groups at their vertices. The assembly does not interfere with H-bonding between the UPy groups, which link the discrete metallacycles into a supramolecular network, leaving the B21C7 groups free for functionalization via host-guest chemistry. The resultant network results in a cavity-cored metallogel at high concentrations or upon solvent swelling. The light-emitting properties of the dialkylammonium substrates were transferred to the network upon host-guest binding. This method is compatible with any dialkylammonium substrate that does not disrupt coordination nor H-bonding, and thus, the unification of these three orthogonal interactions represents a simple yet highly efficient strategy to obtain supramolecular polymeric materials with desirable functionality.

The Influence of Alkali Metal Cation Size on the Formation and Dissociation of Crown Ether Fullerene Dimers in Electrospray Mass Spectrometry

Crown ether fullerenes, C60H(cr – H), form two different dimers in electrospray ionization mass spectrometry, a noncovalently bound, metal-bridged dimer [C60H(cr – H)]2M+, and a singly bonded fullerene dimer of the type (cr – H)–C60–C60–(cr – H)Mnn+, with n = 1, 2. In this work, the dependence of both the formation and the dissociation of these dimers on the respective sizes of the crown ether moiety (12cr4, 15cr5, 18cr6) and of the alkali metal ion (M+ = Li+, Na+, K+, Rb+, Cs+) is studied. The size ratio of crown ether cavity to metal cation size has a profound influence on the formation of the noncovalent dimers, [C60H(cr – H)]2M+. These are only formed if the cation is larger than the crown ether cavity. Also, the doubly charged, covalent dimers [C60(cr – H)]2M22+ show a dependence on the size ratio. The proposed formation mechanism involves the recombination of two C60(cr – H)M•+ radical cations, which can only occur if the repulsion between the two charges is sufficiently reduced by encapsulating the...

Supramolecular Dimerization and [2 + 2] Photocycloaddition Reactions of Crown Ether Styryl Dyes Containing a Tethered Ammonium Group: Structure-Property Relationships.

Molecular self-assembly is an effective strategy for controlling the [2 + 2] photocycloaddition reaction of olefins. The geometrical properties of supramolecular assemblies are proven to have a critical effect on the efficiency and selectivity of this photoreaction both in the solid state and in solution, but the role of other factors remains poorly understood. Convenient supramolecular systems to study the structure-property relationships are pseudocyclic dimers spontaneously formed by styryl dyes containing a crown ether moiety and a remote ammonium group. New dyes of this type were synthesized to investigate the effects of structural and electronic factors on the quantitative characteristics of supramolecular dimerization and [2 + 2] photocycloaddition in solution. Variable structural parameters for the styryl dyes were the size and structure of macrocyclic moiety, the nature of heteroaromatic residue, and the length of the ammonioalkyl group attached to this residue. Quantum chemical calculations of the pseudocyclic dimers were performed in order to interpret the relationships between the structure of the ammonium dyes and the efficiency of the supramolecular photoreaction. One of the dimeric complexes was obtained in the crystalline state and studied by X-ray diffraction. The results obtained demonstrate that the photocycloaddition in the pseudocyclic dimers can be dramatically affected by the electronic structure of the styryl moieties, as dependent on the electron-donating ability of the substituents on the benzene ring, and by the conformational flexibility of the pseudocycle, which determines the mobility of the olefinic bonds. The significance of electronic factors is highlighted by the fact that the photocycloaddition quantum yield in geometrically similar dimeric structures varies from ≤10(-4) to 0.38. The latter value is unusually high for olefins in solution.

Improvement of chiral stationary phases based on cinchona alkaloids bonded to crown ethers by chiral modification.

To improve the chiral recognition capability of a cinchona alkaloid crown ether chiral stationary phase, the crown ether moiety was modified by the chiral group of (1S, 2S)-2-aminocyclohexyl phenylcarbamate. Both quinine and quinidine-based stationary phases were evaluated by chiral acids, chiral primary amines and amino acids. The quinine/quinidine and crown ether provided ion-exchange sites and complex interaction site for carboxyl group and primary amine group in amino acids, respectively, which were necessary for the chiral discrimination of amino acid enantiomers. The introduction of the chiral group greatly improved the chiral recognition for chiral primary amines. The structure of crown ether moiety was proved to play a dominant role in the chiral recognitions for chiral primary amines and amino acids.

Investigation on silver complexes of novel 1,2,3-triazole linked crown ethers by NMR analysis

The novel derivatives of 1,2,3-triazole linked crown ethers were investigated towards silver(I) ion coordination. The NMR measurements in deuterated methanol in different ratios of ligand and silver cation were studied. The experiments were performed in order to examine the way of binding Ag(I) ion by the selected ligands. The results are presented for complexes with the Ag:L stoichiometry 0.5:1, 1:1 and 2:1, respectively. Depending on the type of crown ether moiety incorporated into the macrocyclic skeleton, interesting differences in the mode of stepwise coordination of the ion were noticed. The novel derivatives of 1,2,3-triazole-linked crown ethers were investigated towards silver(I) ion coordination. The presented results show different modes of binding of the metal ion depending on the crown ether moiety incorporated into the macrocyclic skeleton.

Relaxation Photoprocesses in a Crowned Styryl Dye and its Metal Complex.

The effects of solvent and crown-ether moiety on spectral properties of pyridinium styryl dye were studied by steady-state absorption and fluorescent spectroscopy. Analysis of viscosity and polarity effects on fluorescence quantum yield and Stokes shift permitted us to suggest that there is a two stage process of excited state relaxation. The macrocyclic moiety has a little influence on the first stage of relaxation, which manifests itself in a magnitude of Stokes shift, but suppresses considerably the second stage, which manifests itself in a magnitude of fluorescence quantum yield. The metal complex shows an additional stage of excited state relaxation, namely, photorecoordination of metal cation within the macrocyclic cavity.

New NO donor ligands and complexes containing furfuryl or crown ether moiety: Syntheses, crystal structures and tautomerism in ortho-hydroxy substituted compounds as studied by UV–vis spectrophotometry

NO donor ligands were prepared by the condensation of methoxy substituted salicylaldehyde with 5-methylfurfurylamine (1 and 2) and 4′-aminobenzo-15-crown 5 (3–5). New crown ether ligands of Schiff base type (3–5) containing recognition sites for alkali metal and transition guest cations. Ni(II) complexes (1a–5a) have been synthesized with bidentate NO donor Schiff base ligands (1–5) with Ni(CH3COO)2.·4H2O. Monotopic crystalline 1:1 (Na+:ligand) sodium complexes (3b–5b) of the crown ether ligands were also prepared. Schiff bases (1–5) and complexes (1a–5a, 3b–5b) were characterized by elemental analyses, FT-IR, 1H-, 13C-NMR and mass spectroscopies. The crystal structures of 1, 1a and 2 were verified by X-ray diffraction analysis. The tautomeric equilibria (phenol-imine, O–H⋯N and keto-amine, O⋯H–N forms) have been systematically studied by using UV–vis spectrophotometry for the o-hydroxy substituted compounds (1–5). The UV–visible spectra of these ligands (1–5) were recorded and commented in polar, non-polar, acidic and basic media.

Efficient Self-Assembly of Di-, Tri-, Tetra-, and Hexavalent Hosts with Predefined Geometries for the Investigation of Multivalency.

Coordination-driven self-assembly of differently shaped di- to hexavalent crown-ether host molecules is described. A series of [21]crown-7- and [24]crown-8-substituted bipyridine and terpyridine ligands was synthetized in a "toolbox" approach. Subsequent coordination to 3d transition metal and ruthenium(II) ions provides an easy and fast access to host assemblies with variable valency and pre-defined orientations of the crown-ether moieties. Preliminary isothermal calorimetry (ITC) titrations provided promising results, which indicated the host complexes under study to be suitable for the future investigation of multivalent and cooperative binding. The hosts described herein will also be suitable for the construction of various multiply threaded mechanically interlocked molecules.

The low temperature radiolysis of cis-syn-cis- dicyclohexano-18-crown-6 complexes with alkaline earth metal nitrates: An evidence for energy transfer to the macrocyclic ligand

Abstract Formation of paramagnetic intermediates in macrocyclic complexes of cis-syn-cis-dicyclohexano-18-crown-6 (DCH18C6) with alkaline earth metal nitrates under X-rays irradiation was studied by EPR spectroscopy. NO 3 2 - dianions appear to be predominant intermediate species in the samples irradiated at 77 K at low doses (up to 40 kGy). This result was interpreted as an evidence for energy transfer within the complex from crown ether to nitrate anion. Increase in the absorbed dose from 40 kGy to 284 kGy results in built-up of a new EPR signal assigned to macrocyclic –CH2–ĊH–O– radicals produced from crown ether moieties. Thermal annealing of the irradiated macrocyclic complexes at 273 К led to fast decay of NO 3 2 - . This process was accompanied by a formation of –CH2–ĊH–O– radicals in secondary reactions. The nature of the metal cations coordinated in the macrocycle cavity had no appreciable effect on the composition of radical products and their post-radiation transformations.

Structure and Electrical Properties of the Selected Crown Ether-Derivatized Bis(2,2'-bithienyl)Methanes in Langmuir-Blodgett Films

Physical properties of thin films of thiophene derivatives and their polymers are greatly affected by the structure and orientation of their molecules, as well as the local environment.1 In order to obtain thin films of such compounds for practical applications, from electronic devices to chemo- and biosensors.2-3, it is important to control orientation and order of the molecules in the formed functional materials. Interesting and efficient way to allow for such a control is Langmuir and Langmuir-Blodgett technique. In the presented contribution formation and properties of ultrathin films of the series of bis(2,2’-bithienyl)methane derivatives appended with crown ethers of varying size are presented. Uniform Langmuir films of liquid-expanded type were obtained at water-air interface for all of the used compounds. The influence of metal ions on the orientation of the molecules in the films was relatively small. Obtained Langmuir films were subsequently transferred onto the solid substrates by using Langmuir-Blodgett technique forming mono- and multilayers. In order to further elucidate structure of the formed layers AFM and STM techniques have been applied. The morphology of the multilayer films depended both on the size and orientation of the crown ether moiety in the molecules. However, in all cases formed multilayers were porous (Fig. 1). In case of monolayers, the STM studies helped to ascertain organization of the molecules in the Langmuir-Blodgett film. On the other hand the scanning tunnelling spectroscopy (STS) allowed acquisition of information about the electrical properties of the studied thiophene derivatives. Bibliography 1. D. Hu, J. Yu, K. Wong, B. Bagchi, P. J. Rossky, P. F. Barbara, Nature, 405, (2000), 1030. 2. A. G. MacDiarmid, Angew. Chem., Int. Ed., 40, (2001),2581. 3. R. Singhal, A. Chaubey, K. Kaneto, W. Takashima, B. D. Malhotra, Biotechnol. Bioeng., 85 (2004), 277. Figure 1

Sodium Ion Complexation Enforced Columnar Mesophase of Dibenzo[a,c]phenazine Bearing Lateral Crown Ether

The dibenzo[a,c]phenazine discogen having “π-polarization” containing a lateral crown ether and four alkoxy-peripheral side chain, DBPZ-Cn were synthesized. These metal-free crown ether DBPZ-Cn having four dodecylalkoxy side chains were found to be non-mesogenic. The columnar mesophase can be augmented by complexation of the crown ether moiety with sodium ion for DBPZ-C12-Na. XRD investigation revealed the formation of rectangular columnar mesophase for DBPZ-C12-Na.

Synthesis and spectroscopic characterization of Y-shaped fluorophores with an imidazole core containing crown ether moieties

In this study three new Y-shaped fluorophores, 4,5-(2,2'-diphenyl)vinyl-{2-[(1,4,7,10-tetraoxa-13-azacyclopentadecyl)phenyl]}-1H-imidazole (1a), 4,5-{[2,2'-bis(4-methoxyphenyl)vinyl]-[2-(1,4,7,10-tetraoxa-13-azacyclopentadecyl)-phenyl]}-1H-imidazole (1b) and 4,5-(2,2'-diphenyl)vinyl-{2-(1,4,7,10,13-benzopentaoxacyclopentadecyl)}-1H-imidazole (1c) were synthesized. 1,6-Diphenylhexa-1,5-diene-3,4-dione (2a) and 1,6-bis(4-methoxyphenyl)hexa-1,5-diene-3,4-dione (2b) were synthesized as preliminary fluorophores and then reacted with 4-formylbenzo-aza-15-crown-5 (3a) and 4-formylbenzo-15-crown-5 (3b) to obtain the three Y-shaped fluorophores 1a, 1b and 1c. 4-formylbenzo-aza-15-crown-5 and 4-formylbenzo-15-crown-5 intermediates were synthesized with Vilsmeier–Haack reaction. The photophysical properties such as maximum absorption wavelengths, maximum emission wavelengths, Stokes' shifts, singlet energies, fluorescence quantum yields and photostabilities of the compounds were investigated by measuring absorption and emission spectra in a series of solvents of varying polarities of toluene (TOL), dichloromethane (DCM), tetrahydrofuran (THF), ethyl acetate (EA), acetonitrile (ACN), and N,N-dimethylformamide (DMF). The three compounds 1a, 1b and 1c exhibited emission maxima in the 412–677nm range. All the derivatives synthesized exhibited excellent photostability in all the solvents tested.

Positive and negative allosteric effects of thiacalix[4]arene-based receptors having urea and crown-ether moieties

Allosteric binding behaviors of heteroditopic receptors bearing the 1,3-alternate conformation based thiacalix[4]arene have been evaluated by absorption and 1H NMR titration experiments.

Preparation and evaluation of novel chiral stationary phases based on quinine derivatives comprising crown ether moieties.

The C9-position of quinine was modified by meta- or para-substituted benzo-18-crown-6, and immobilized on 3-mercaptopropyl-modified silica gel through the radical thiol-ene addition reaction. These two chiral stationary phases were evaluated by chiral acids, amino acids, and chiral primary amines. The crown ether moiety on the quinine anion exchanger provided a ligand-exchange site for primary amino groups, which played an important role in the retention and enantioselectivity for chiral compounds containing primary amine groups. These two stationary phases showed good selectivity for some amino acids. The complex interaction between crown ether and protonated primary amino group was investigated by the addition of inorganic salts such as LiCl, NH4Cl, NaCl, and KCl to the mobile phase. The resolution results showed that the simultaneous interactions between two function moieties (quinine and crown ether) and amino acids were important for the chiral separation.

Synthesis, Structure, and Properties of Supramolecular Photoswitches Based on Ammonioalkyl Derivatives of Crown Ether Styryl Dyes

The synthesis of new styryl dyes derived from 4-pyridine and 4-quinoline and having an ammonioalkyl N-substituent and benzocrown ether moieties of different sizes and with different sets of heteroatoms was developed. Spontaneous "head-to-tail" dimerization of these dyes via the formation of numerous hydrogen bonds between the terminal NH3(+) groups and crown ether moieties was detected in MeCN solutions. The stability constants of the dimeric complexes having pseudocyclic structure were studied by (1)H NMR titration. The most stable complexes (log Kd up to 8.2) were found in the case of dyes with the 18-crown-6 ether moiety, which is most complementary for binding a primary ammonium group. Stacking interaction of the conjugated systems in the dimeric complexes contributes to their stability to a much lesser extent. In dimeric complexes, the ethylene bonds of the dyes are preorganized for stereospecific [2 + 2] photocycloaddition (PCA) induced by visible light. PCA yields only rctt isomers of bis-crown-containing cyclobutane derivatives. The dyes were studied by X-ray diffraction; it was found that the dimeric arrangement is also retained in the crystalline state. The possibility of topochemical PCA of the dyes in single crystals without their destruction was demonstrated. The possibility of retro-PCA of the obtained cyclobutane derivatives to give the starting dyes was shown. The elucidated regularities of PCA can be used to fabricate optical data recording systems based on ammonioalkyl derivatives of crown ether styryl dyes.

Fluorescence of Kryptofix 5 metal complexes

Kryptofix 5 forms complexes with a variety of metal cations. The coordination with the crown ether moiety affects only slightly the emission wavelength of the free Kryptofix 5 ligand (λmax=425nm) in a buffer (pH=9) solution, but the emission intensity of this blue fluorescence can increase strongly upon complex formation, probably owing to the rigidity of the complex. This applies e.g. to Ba2+, Zn2+, Cd2+, Hg2+, Ag+ and La3+. A second group of metal ions such as Al3+, Pb2+, Sb3+, Bi3+, Te4+, Gd3+ and Th4+ causes a large red shift of the fluorescence of free Kryptofix 5 to approximately λmax=500nm. This green fluorescence resembles that of Kryptofix 5 in acidic solution. It is suggested, that the second group of metal ions is also coordinated to the pyridine nitrogen atoms of the quinoline substituents.

High functional nano materials for ophthalmic lenses containing silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) and silicon 2,9,16,23-tetra-tert-butyl-29H31 H-phthalocyanine dihydroxide.

High functional ophthalmic lens materials, poly(HEMA-co-GMA)s were prepared by the copolymerization of HEMA, MMA, NVP, EDGMA and GMA in the presence of SiNc [silicon 2,3-naphthalocyanine bis(trihexylsilyloxide)] and SiPc (silicon 2,9,16,23-tetra-tert-butyl-29H31H-phthalocyanine dihydroxyde). Also, the physical and optical characteristics of the produced polymers were analyzed to investigate UV-blocking capabilities of these functional ophthalmic dyes and their applicability as materials for colored hydrogel contact lenses. For G_SN samples to which GMA was added to the Ref._SN combination, the transmittance for visible ray, UV-B and UV-A was in the range of 86.0-89.4%, 63.0-67.6% and 62.5-66.0% respectively. Also, for G_SP samples, the transmittance for visible ray, UV-B and UV-A was in the range of 85.2-87.0%, 70.0-72.6 and 68.0-70.2% respectively. The measurement of the spectral transmittance showed that both SiNc and SiPc absorbed a small amount of UV light, but the absorption pattern for UV light differed for each material. Based on the results, the addition of SiNc and SiPc to ophthalmic polymer materials can be used for various purposes in colored ophthalmic lens that are capable of offering protection from UV and infrared light without significant change of the physical properties.

Functionalized Mesoporous Silicas with Crown Ether Moieties for Selective Adsorption of Lithium Ions in Artificial Sea Water

Lithium ion has been increasingly recognized in a wide range of industrial applications. In this work, we studied on the adsorption of Li+ in the artificial seawater with high selectivity using methyl-crown ether (AC-SBA-15) and aza-crown ether (HMC-SBA-15) moieties-functionalized mesoporous silica materials. First, methyl-crown ether and aza-crown ether moieties-functionalized mesoporous silica materials were synthesized via two-step post-synthesis process using a grafting method. The functionalized materials were employed to the metal ion adsorption from aqueous solution (artificial seawater) containing Li+, Co2+, Cr3+ and Hg2+. The prepared hybrid material showed high selectivity for Li+ ion in the artificial seawater at pH 8.0. The absorbed amount of Li+ was 73 times higher than Cr3+ for aza-crown ether containing AC-SBA-15 as an absorbent. The absorbed amount of Co2+ (4.5 x 10(-5) mol/g), Cr3+ (1.5 x 10(-5) mol/g) and Hg2+ (2.25 x 10(-4) mol/g) were remarkably lower than the case of Li+. On the other hand, the absorbed amount of various metal ions of HMC-SBA-15 with amine groups in alky chains and crown ether moieties were 1.1 x 10(-3) mol/g for Li+, 5.0 x 10(-5) mol/g for Co2+, 2.9 x 10(-4) mol/g for Cr3+, 2.8 x 10(-4) mol/g for Hg2+ mol/g, respectively.

Robust inclusion complexes of crown ether fused tetrathiafulvalenes with Li⁺@C₆₀ to afford efficient photodriven charge separation.

Inclusion complexes of benzo- and dithiabenzo-crown ether functionalized monopyrrolotetrathiafulvalene (MPTTF) molecules were formed with Li(+)@C60(1⋅Li(+)@C60 and 2⋅Li(+)@C60). The strong complexation has been quantified by high binding constants that exceed 10(6) M(-1) obtained by UV/Vis titrations in benzonitrile (PhCN) at room temperature. On the basis of DFT studies at the B3LYP/6-311G(d,p) level, the orbital interactions between the crown ether moieties and the π surface of the fullerene together with the endohedral Li(+) have a crucial role in robust complex formation. Interestingly, complexation of Li(+)@C60 with crown ethers accelerates the intersystem crossing upon photoexcitation of the complex, thereby yielding (3)(Li(+)@C60)*, when no charge separation by means of (1)Li(+)@C60* occurs. Photoinduced charge separation by means of (3)Li(+)@C60* with lifetimes of 135 and 120 μs for 1⋅Li(+)@C60 and 2⋅Li(+)@C60, respectively, and quantum yields of 0.82 in PhCN have been observed by utilizing time-resolved transient absorption spectroscopy and then confirmed by electron paramagnetic resonance measurements at 4 K. The difference in crown ether structures affects the binding constant and the rates of photoinduced electron-transfer events in the corresponding complex.