Crown Ether Chain Research Articles

Solvent effects on the interaction between alkali metal cations and 1,3-Diisopropoxycalix [4] arenecrown-6: Nuclear magnetic resonance spectroscopy and Independent Gradient Model Non-Covalent interactions analysis

The combination of 1,3-Diisopropoxycalix [4] arenecrown-6 (BPC6) and alkali metal ions were studied in different solvents by 1H and 133Cs Nuclear magnetic resonance (NMR) spectra, gmx_MMPBSA, and Independent Gradient Model (IGM) non-covalent interactions analysis based on Molecular Dynamics (MD) Simulations. The binding energy of BPC6·M+ complex follows the order: BPC6·Cs+ > BPC6·Rb+ > BPC6·K+ in CHCl3, which is completely reverse to that in vacuum. In addition, the coordination properties depend on solvent polarity: In the low polarity solvent such as CHCl3, all the oxygens in crown ether chain of BPC6 are involved in the coordination with Cs+ ions. By comparison, in the high polarity solvents such as CH3CN and CH3OH, the number of oxygens participates in the complexation decreases, and the cation-π interaction areas of complexes are also reduced. That is because the contribution of electrostatic interactions in complexation is weakened by solvent effect. The cation-π interaction plays a very important role in selectivity among alkali metal cations and coordination stability of BPC6·M+ complex in different solvents.

Synthesis of Pyridine-Containing Crowned Fused Expanded Porphyrins.

New examples of nonaromatic fused expanded porphyrins containing both pyridine and crown ether moiety as a part of macrocyclic framework were synthesized by condensing pyridine based pentapyrrane with polyether-based diol in CH2 Cl2 in the presence of one equivalent of BF3 ⋅ OEt2 under inert conditions followed by oxidation with DDQ in open air. The condensation was expected to form pyridine-containing crowned expanded porphyrins but resulted in the formation of fused crowned expanded porphyrins due to intramolecular fusion of two pyrrole nitrogens with two adjacent inverted thiophene carbons as revealed by X-ray crystallography obtained for one of the macrocycle. HRMS and NMR studies supported the formation of fused crowned pyridine containing expanded porphyrins, and the macrocycles showed simple, well-resolved NMR spectra where all resonances were identified easily by 2D NMR spectroscopy. The macrocycles exhibited typical nonaromatic absorption features and showed one broad band with peak maxima at 535 nm and one or two shoulder bands in the higher energy region. The protonation studies resulted in clear colour change from purple to blue and absorption bands experienced bathochromic shifts with a broad band at 662 nm which was extended up to 800 nm. The electrochemical studies revealed that the macrocycles were easier to oxidize but difficult to reduce. DFT studies indicated that the macrocycle attains a very puckered and distorted 'U' shaped structure owing to the flexibility of the crown ether chain and TD-DFT studies corroborated experimental results. The preliminary studies indicated that the macrocycles could be used as colorimetric optical sensor for the detection of Cu2+ ion.

Bis-biphenylacrylonitrile bridged with crown ether chain: a novel fluorescence sensor for Fe3+ in aqueous media

A novel fluorescence sensor for Fe3+ in aqueous media was developed and applied for living-cell imaging.

A novel fluorescence sensor for K + based on bis-Bodipy: The ACQ effect controlled by cation complexation of pseudo crown ether ring

Three novel bis-Bodipy 3a-3c bridged with crown ether chain were prepared in yields of 70∼78%. Their complexation absorption and fluorescent spectra for fourteen metal ions suggested that compound 3b exhibited the selective response for K+ with obvious ACQ effect. The association constant of compound 3b with K+ was 4.3×105 M-1 and 1:1 complex mode was deduced. The complexation mechanism of ACQ effect controlled by cation complexation of pseudo crown ether ring was confirmed by the fluorescent titrations, complexation FT-IR spectra, complexation 1H NMR spectra, complexation ESI-MS spectra and contrast experiment of similar mono-Bodipy derivative. The K+ was binded in the cavity of a pseudo crown ether ring, leading to the closed distance for two Bodipy units and then enhancing the ACQ effect obviously. Both the structure of the crown ether chain and two Bodipy units were decisive factors for the selective fluorescence sensor for K+.

Iptycene-derived crown ether hosts for molecular recognition and self-assembly.

CONSPECTUS: Synthetic macrocyclic hosts have played key roles in the development of host-guest chemistry. Crown ethers are a class of macrocyclic molecules with unique flexible structures. They have served as the first generation of synthetic hosts, and researchers have extensively studied them in molecular recognition. However, the flexible structures of simple crown ethers and their relatively limited modes of complexation with guests have limited the further applications of these molecules. In recent years, researchers have moved toward fabricating interlocking molecules, supramolecular polymers, and other assemblies with specific structures and properties. Therefore, researchers have developed more complex crown ether-based macrocyclic hosts with multicavity structures and multicomplexation modes that provide more diverse and sophisticated host-guest systems. In this Account, we summarize our research on the synthesis and characterization of iptycene-derived crown ether hosts, their use as host molecules, and their applications in self-assembled complexes. Iptycenes including triptycenes and pentiptycenes are a class of aromatic compounds with unique rigid three-dimensional structures. As a result, they are promising building blocks for the synthesis of novel macrocyclic hosts and the construction of novel self-assembled complexes with specific structures and properties. During the last several years, we have designed and synthesized a new class of iptycene-derived crown ether hosts including macrotricyclic polyethers, molecular tweezer-like hosts, and tritopic tris(crown ether) hosts, which are all composed of rigid iptycene building blocks linked by flexible crown ether chains. We have examined the complexation behavior of these hosts with different types of organic guest molecules. Unlike with conventional crown ethers, the combination of iptycene moieties and crown ether chains provides the iptycene-derived crown ether hosts with complexation properties that differ based on the structure of the guests. The rigid iptycene moieties within these synthetic host molecules both maintain their inherent three-dimensional cavities and generate multicavity structures. The flexible crown ether chains allow the iptycene-derived hosts to adjust their conformations as they encapsulate guest molecules. Moreover, the expanded complexation properties also allow the host-guest systems based on the iptycene-derived crown ethers to respond to multiple external stimuli, resulting in a variety of supramolecular assemblies. Finally, we also describe the construction of mechanically interlocked self-assemblies, molecular switches/molecular machines, and supramolecular polymers using these new host molecules. We expect that the unique structural features and diverse complexation properties of these iptycene-derived crown ether hosts will lead to increasing interest in this field and in supramolecular chemistry overall.

ChemInform Abstract: Structures of Two Crown Ether Derivatives of 9-Acridone.

(I) N-Methyl-2,5,8,11,14,17,20-heptaoxa-25-azatetracyclo[19.7.5.0(24,32),0(26,30)]tritriaconta-1 (29),-21(33),22,24(32),26(30),27-hexaen-31-one trihydrate, C26H33NO8.3H2O, M(r) = 541.6, triclinic, P1BAR, a = 7.389 (1), b = 13.255 (1), c = 14.448 (2) angstrom, alpha = 88.60 (1), beta = 78.58 (1), gamma = 81.48 (1)-degrees, V = 1371.7 (2) angstrom 3, Z = 2, D(x) = 1.31 g cm-3, lambda(Cu K-alpha) = 1.54178 angstrom, mu = 8.68 cm-1, F(000) = 580, T = 291 K, R = 0.047 for 3376 observed reflections. (II) N-Methyl-2,5,8,11,14,17-hexaoxa-22-azatetracylco[16.7.5.0.(21,29).0(23,27)]triaconta-1 (26), 18(30), 19,-21(29),23(27),24-hexaen-28-one, C24H29NO7, M(r) = 443.5, triclinic, P1BAR, a = 8.426 (2), b = 11.420 (2), c = 11.739 (4) angstrom, alpha = 87.20 (3), beta = 79.33 (3), gamma = 77.88 (2)-degrees, V = 1085.3 (5) angstrom 3, Z = 2, D(x) = 1.36 g cm-3, lambda(Mo K-alpha) = 0.71069 angstrom, mu = 1.08 cm-1, F(000) = 472, T = 291 K, R = 0.039 for 3229 observed reflections. In these substituted acridone derivatives one molecule contains both a crown ether moiety with its complexing capabilities and a heterocyclic N atom able to modify these properties. In the two compounds, the crown ether chain is nearly perpendicular to the acridinic skeleton which is planar. In (I) the water molecules take part in hydrogen bonds with the crown ether [O37...O11 = 3.03 (1), O35...O36 = 2.81 (1) angstrom] and with each other [O36...O37 = 2.93 (1), O38...O36 = 2.84 (1), O38...O37 (x + 1, y, z) = 2.89 (1) and O38...O37 (1 - x, 1 - y, 1 - z) = 2.88 (1) angstrom]. The bond lengths suggest partial localization of double bonds in the benzene rings.

The synthesis and electrochemical study of novel phthalocyanines substituted with a crown ether and alkyl chains

A new class of soluble unsymmetrically substituted metallophthalocyanines (M = Zn, Ni, Co) bearing a crown ether and six alkylthio substituents was synthesized and their electrochemical and spectroelectrochemical properties studied. Cyclic and square wave voltammetry revealed well-defined ligand-based oxidation and reduction processes within the complexes. Assignment of the redox processes was performed by in-situ spectroelectrochemical measurements. The disappearance of the redox processes for the monomeric species and the observation of new waves indicated that intermolecular dimer formation occurred during the potentiometric titration of the complexes with K + and Na + ions.

Complexation of a Pentiptycene-Based Tweezer-Like Receptor with Paraquat Derivatives: Ion-Controlled Binding and Release of the Guests

A new tweezer-like receptor containing a pentiptycene unit and a benzene ring linked by two crown ether chains has been synthesized. It could form stable complexes with paraquat derivatives with different functional groups in solution and in the solid state. It was found that the complexes dissociated upon two one-electron reduction of the bipyridinium ring. Moreover, binding and release of the guest molecules could also be easily controlled by the addition and removal of potassium ion.

Crown Ether Vinylogous Tetrathiafulvalene Receptors: Complexation Interference on the Molecular Movements Triggered by Electron Transfer

The synthesis of a series of crown ether substituted vinylogous tetrathiafulvalenes (TTFVs) has been carried out through oxidative coupling of bisdithiafulvenes. These new receptors have been fully characterized using electrochemical, spectroelectrochemical, and molecular modeling experiments. These studies show that, upon oxidation, either a clip movement (TTFVs 3a,b) or a stretch movement (TTFV 3c) occurs, depending on the length of the crown ether chains. Preliminary electrochemical studies, undertaken on TTFV 3c in dichloromethane, show a little shift of the first standard oxidation potential toward more positive values upon addition of the Pb(2+) ion, but a considerable variation of the electron-transfer kinetics. This result introduces an interesting concept for the preparation of sensors not based on thermodynamic variations but on kinetic modifications of the electron transfer.

Sodium Ion Effect on Photoinduced Electron Transfer of Porphyrin-Crown Ether-Affixed Quaterthiophene-[60]Fullerene Triad as a Gated Molecular Switch

A porphyrin-quaterthiophene-fullerene triad, in which the center of the quaterthiophene spacer is additionally bridged with a crown ether chain in a sash manner has been newly synthesized. Photoinduced charge-separation (CS) and charge-recombination processes in the absence and presence of Na+ have been investigated by time-resolved fluorescence and transient absorption spectroscopic methods.

Application of Photoresponsive Polymers Carrying Crown Ether and Spirobenzopyran Side Chains to Photochemical Valve

A vinyl copolymer carrying crown ether and spirobenzopyran side chains, which undergoes significant photoinduced rheology changes, i.e., contraction and extension of its polymer chain, was applied to a material for photocontrol system of solvent permeation rate, so-called, photochemical valve. Macroporous polyethylene membranes coated by the crown ether-spirobenzopyran copolymer can work as a functional membrane controlling solvent permeation rate photochemically. UV-light irradiation on the photoresponsive membrane decreased the permeation rate of hexane, due to the increased polarity of the membrane pore, which was in turn derived from the photoisomerization of its spirobenzopyran moiety to the corresponding ionic merocyanine form. The following visible-light irradiation on the membrane restored the permeation rate by isomerization back to the electrically neutral spiropyran form. To the contrary, the permeation of ethanol through the membrane was enhanced by UV-light irradiation due to the increase in the apparent membrane pore size induced by the polymer chain contraction and vice versa by visible light. Similar photoresponses in the permeation rate of nonpolar and polar solvents were also observed with a sintered glass filter modified chemically by both silane-coupling reagents containing crown ether and spirobenzopyran moieties.

Supramolecular Pseudo‐Rotaxane Type Complexes from π‐Extended TTF Dimer Crown Ether and C60.

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Supramolecular pseudo-rotaxane type complexes from π-extended TTF dimer crown ether and C 60

A new cyclophane-type crown ether endowed with two exTTF units forms supramolecular ensembles with different dibenzylammonium salts with a binding constant of K a∼50 M −1 determined by 1H NMR and fluorescence experiments. Cyclic voltammetry studies show the existence of electronic interaction between the exTTF units due to the flexible nature of the crown ether chains.

Synthesis and complexation properties of two new curcuminoid molecules bearing a diphenylmethane linkage

Bis-curcuminoids 3 and 4, bearing a diphenylmethane bridge for both compounds and a crown ether chain adapted to complex Li + for compound 4, were synthesized and characterized by mass and NMR spectroscopies. By their preorganized geometry, they represent a new class of curcuminoids able to complex transition metal cations. Their absorption spectra in DMF by comparison with those of curcumin 1 and dimethylcurcumin 2 have shown that the phenolate forms in the two halves are in interaction in compound 3 and are independent in compound 4. Complexation studies have revealed a poor selectivity of curcuminoids for transition metals. Nevertheless complexation of Cu (II), studied by UV–visible absorption spectroscopy, has shown subtle differences between curcumin 1 and bis-curcuminoid 3. These observations were supported by quantum mechanic calculations to establish the most probable structures of non- and complexed compounds.

Anisotropic thermal expansion in 18-crown-6·2 H2O·2 HNO3

Reaction of aqueous HNO3 with 18-crown-6 results in the isolation of the neutral inclusion compound 18-crown-6·2 H2O·2 HNO3. Variable temperature single crystal X-ray and neutron diffraction data reveal that the triclinic (P) unit cell undergoes a highly anisotropic change in shape with temperature, with the crystallographic β angle changing smoothly from 66.56° to 69.03° between room temperature and 20 K. This arises from a change in shape of the crown ether in response to increases in hydrogen bond distances in the HNO3⋯H2O⋯crown ether chain.

Ordering of a lateral crown ether and terminal short POE chains in some symmetrical nematogens by 13 C NMR

A lateral crown ether fragment can be introduced on symmetrical mesogens containing only three aromatic rings. The replacement of the terminal alkoxy chains by chains containing oxyethylene units decreases the melting and clearing temperatures allowing one to obtain nematic compounds near room temperature. These compounds dissolve LiBF4 salt only to a small extent, but the nematic arrangement, is thereby destroyed. The carbon chemical shift anisotropy and the local C-H bond order parameters were obtained for the nematic phase for the crown ether fragment and the terminal chains. This study indicates that the crown ether average conformation changes insignificantly on decreasing the temperature. The lateral crown ether protrudes markedly from the core with the consequence that the molecular shape is far from rod-like in geometry.

First- and second- sphere coordination of the uranyl ion by bis[2-(2-hydroxyphenoxy)ethoxy]ethane

Uranyl nitrate hexahydrate reacts with bis[2-(2-hydroxyphenoxy)ethoxy]ethane (C(18)H(22)O(6)), denoted LH(2) hereafter, in the presence of triethylamine to give triethylammonium aqua[2,2'-(3,6-dioxaoctane-1,8-diyldioxy)diphenolato-kappa(2)O,O'](nitrato-kappa(2)O,O')dioxouranium(VI), (Et(3)NH)[UO(2)(H(2)O)L(NO(3))], which possesses a symmetry plane. The uranyl ion is coordinated to the two phenoxide O atoms, a nitrate ion and a water molecule (first sphere); the water molecule is itself held in the crown ether chain by hydrogen-bonding interactions, thus ensuring second-sphere coordination by the ligand L.

(9,10-Triptyceno)benzo-28-crown-8

The structure of the title compound, C40H44O8, differs from previously determined structures of triptyceno–crown ether mol­ecules as its longer crown ether chain does not congest a triptycene cavity.

Self-Assembly of Novel Polyrotaxanes: Main-Chain Pseudopolyrotaxanes with Poly(ester crown ether) Backbones.

Not threading rings on chains, but chains through rings results in a new class of main-chain polyrotaxanes. The cations of bipyridinium salts thread through the crown ether units of a poly(ester crown ether) chain (shown below). The threading efficiency m/n of the polyrotaxane is controlled by stoichiometry and temperature.

Crystal Structures of 1,3-Calix[4]-bis-crown-6·3CH3CN and 1,3-Calix[4]-bis-(benzo-crown-6)·3 CH3CN

The crystal structures of a new solvate of the ditopic receptor 1,3-calix[4]-bis-crown-6, Bis-C6, and of 1,3-calix[4]-bis-(benzo-crown-6), Bis-benzoC6, are reported. Bis-C6.3 CH3CN (1) crystallizes in the monoclinic space group P21/n, a = 14.388(3), b = 26.947(8), c = 14.707(4) A, β = 113.19(3)°, V = 5241(5) A3, Z = 4. Refinement led to a final conventional R value of 0.092 for 2723 reflections. The structure of (1) differs from the previously reported structure of Bis-C6.4 CH3CN by the conformation of one crown either chain. Two acetonitrile molecules are in the close neighbourhood of the crown ether cavities. Bis-benzoC6.3 CH3CN (2) crystallizes in the monoclinic space group P21/c, a = 10.391(4), b = 17.264(11), c = 30.426(9) A, β = 94.62(3)°, V = 5440(7) A3, Z = 4. Refinement led to a final conventional R value of 0.106 for 2965 reflections. Two acetonitrile molecules are located near the crown ether cavities, as in (1). One of the crown ether conformations is the same as in the binuclear caesium complex of Bis-benzoC6, supporting the hypothesis of a preorganization of this ligand towards the complexation of this ion; the second crown ether chain is partially disordered.