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We report herein the synthesis, structure, and molecular recognition of S6 - and (SO2 )6 -corona[6](het)arenes, and demonstrate a unique and efficient strategy of regulating macrocyclic conformation and properties by adjusting the oxidation state of the heteroatom linkages. The one-pot nucleophilic aromatic substitution reaction of 1,4-benzenedithiol derivatives, biphenyl-4,4'-dithiol and 9,9-dipropyl-9H-fluorene-2,7-dithiol with 3,6-dichlorotetrazine afforded S6 -corona[3]arene[3]tetrazines. These compounds underwent inverse-electron-demand Diels-Alder reaction with enamines and norbornadiene to produce S6 -corona[3]arene[3]pyridazines. Facile oxidation of sulfide linkages yielded (SO2 )6 -corona[3]arene[3]pyridazines. All corona[6](het)arenes adopted generally hexagonal macrocyclic ring structures; however, their electronic properties and conformation could be fine-tuned by altering the oxidation state of the sulfur linkages. Whereas (SO2 )6 -corona[3]arene[3]pyridazines were electron-deficient, S6 -corona[3]arene[3]pyridazines acted as electron-rich macrocyclic hosts that recognized various organic cations in both aqueous and organic solutions.

[(4-Ethoxyanilinum)(18-crown-6)][BF4] (1) single crystals were successfully grown by solution method, with its structure, phase purities, thermal stability, dielectric, absorption and fluorescence spectra were systematically characterized for the first time. The DSC, XRD and dielectric measurements showing that no phase transition occurs in compounds 1 over the temperature ranges of 100–298 K. The absorption edge located in ultraviolet ranges and extended to 300 nm, with strong photoluminescence peak at 296 nm was observed when it was excited at 252 nm by a xenon lamp. All the results make compound 1 promising candidates for optical applications. More importantly, the specific roles of organic and inorganic components of crown compounds were preliminary determined by comparison, which have guiding significance in searching for new compounds with some interesting performances.

OBJECTIVE This study evaluated the loading capacity of CAD/CAM-fabricated anterior feldspathic ceramic crowns bonded to one-piece zirconia implants with different cements. MATERIAL AND METHODS Fifty one-piece zirconia implants were embedded in epoxy resin. The abutment aspect of one implant was optically scanned and a standardized upper canine was designed with CAD-software. Fifty feldspathic ceramic crowns were milled, polished, and mounted on the implants either without any cement, with a temporary cement or with three different composite resin cements after surface pretreatment as recommended by the manufacturers (n = 10). After storage in distilled water at 37°C for 24 hr, specimens were loaded until fracture on the palatal surface of the crown at an angle of 45° to the long axis of the implant and loads until fracture were detected and compared. Compressive strength of the investigated cement materials was determined. Statistical analyses were done with One-way ANOVA followed by post hoc Fisher LSD test (α = 0.05). RESULTS The cements revealed significantly different compressive strength values (temporary cement: 37.1 ± 7.0 MPa; composite resin cements: 185.8 ± 21.3, 277.9 ± 22.1, and 389.0 ± 13.6 MPa, respectively). Load-at-fracture values had an overall mean value of 237.1 ± 58.2 N with no significant difference among the composite resin cements (p > 0.05). Fracture load values with the temporary cement or without cement were significantly lower (p

A non-symmetrical pH-sensitive bistable [2]rotaxane that bears a cholesterol unit and a tetraphenylmethane group as stopper groups was designed and synthesized in 18 steps. The successful formation of the rotaxane was proven by NMR spectroscopy and MS/MS. Besides a permanent cationic alkylated triazolium unit, the axle contains a secondary amine that can act as a second pH-sensitive binding site for a crown ether. Depending on the protonation state of this amine function, the crown ether reversibly changes its position by moving between the two binding sites along the axle, as revealed by NMR spectroscopy.

The results of studies aimed at producing and developing a new methodology of synthesis of functional derivatives of benzoazacrown ethers by stepwise transformation of the benzocrown macrocycle are generalized. The comprehensive study of the spatial structure and complexation properties of the starting benzocrown ethers, target benzoazacrown ethers, and their nearest structural analogs shows that the N-alkylbenzoazacrown derivatives exhibit a much higher ability to bind metal and ammonium cations compared to the corresponding N-phenylazacrown ethers. They are comparable with benzocrown ethers in complexation properties and exceed them in some cases. A new approach to the synthesis of dinitrodibenzodiazacrown ethers is proposed based on the one-step transformation of the macrocycle of the dinitrodibenzo18-crown-6 cis-isomer under the action of aliphatic diamines. The synthesis of styryl dyes containing the N-methylbenzoazacrown fragment is described. The detailed studies by electron spectroscopy, NMR spectroscopy, and X-ray diffraction analysis revealed a high potential of these dyes as optical molecular sensors for alkaline and alkaline-earth metal cations.

International audience; A series of Gd(3+) complexes exhibiting a relaxometric response to zwitterionic amino acid neurotransmitters was synthesized. The design concept involves ditopic interactions 1) between a positively charged and coordinatively unsaturated Gd(3+) chelate and the carboxylate group of the neurotransmitters and 2) between an azacrown ether appended to the chelate and the amino group of the neurotransmitters. The chelates differ in the nature and length of the linker connecting the cyclen-type macrocycle that binds the Ln(3+) ion and the crown ether. The complexes are monohydrated, but they exhibit high proton relaxivities (up to 7.7 mM(-1) s(-1) at 60 MHz, 310 K) due to slow molecular tumbling. The formation of ternary complexes with neurotransmitters was monitored by (1) H relaxometric titrations of the Gd(3+) complexes and by luminescence measurements on the Eu(3+) and Tb(3+) analogues at pH 7.4. The remarkable relaxivity decrease (≈80 %) observed on neurotransmitter binding is related to the decrease in the hydration number, as evidenced by luminescence lifetime measurements on the Eu(3+) complexes. These complexes show affinity for amino acid neurotransmitters in the millimolar range, which can be suited to imaging concentrations of synaptically released neurotransmitters. They display good selectivity over non-amino acid neurotransmitters (acetylcholine, serotonin, and noradrenaline) and hydrogenphosphate, but selectivity over hydrogencarbonate was not achieved.

Functionalized [13.3.3](1,2,4)crownophane 1 was designed and synthesized with the intention to switch the distance between PtII centers by external stimuli when incorporated as a backbone into the ligand of a dinuclear PtII complex. Two benzene rings linked by two propylene bridges build up the cyclophane scaffold of 1. An additional crown ether bridge introduces the feature of varying the opening angle of the cyclophane triggered by cation complexation. The structure and breathing function of crownophane 1 were studied, and it was utilized as backbone ligand in dinuclear PtII complex 2.

The synthesis of a new acridono-18-crown-6 ether type sensor has been carried out starting from commercially available and relatively cheap materials. The cation recognition ability of the new ligand and also a reported analog thereof toward various metal ions was studied in acetonitrile by UV/Vis spectroscopy. Our studies revealed the selective binding of Pb2+ ions by the latter ligand. Based on our calculations, we suggest the formation of a complex with 1:1 ligand to metal ion ratio.

A thiacalix[4]crown based di-topic receptor 3 possessing two types of binding sites viz. crown-5 ring and imino moieties has been synthesized which undergoes fluorescence enhancement in the presence of Zn2+ ions. The selective binding of Zn2+ to compound 3 does not allow the K+ ions to bind with the crown-5 ring and thus a negative allosteric behaviour has been observed between Zn2+/K+ ions. In addition, the 3-Zn2+ complex can be used for the detection of H2PO4− ions with a fluorescence “turn-off” response. Furthermore, based on the fluorescence response, a two input and one output sequential logic circuit has been constructed.

G-quadruplexes (GQs), spatial assemblies of guanine-rich DNA strands, play an important role in the regulation of gene expression and chromosome stabilization. These structures are recognized to be useful in cancer therapies as the presence of multiple G-quadruplexes in a telomeric strand stops cancer cell proliferation. Metallacrowns of the type 12-MC-4 form planar structures that have remarkable similarity to G-tetrads in terms of dimension, shape and the ability to bind alkali metal and lanthanide cations in a central cavity. The interaction between the Sm(iii)[12-MC

A few new d-mannitol-based monoaza-15-crown-5 type chiral lariat ethers and 18-crown-6 type macrocycles were synthesized. These crown compounds were used as phase transfer catalysts in asymmetric Michael addititons and in a Darzens condensation under mild conditions to afford the corresponding products in a few cases in good to excellent enantioselectivities. In the Michael addition of diethyl acetoxymalonate to trans-chalcone, in the addition of diethyl acetamidomalonate to s-nitrostyrene, in the reaction of diethyl bromomalonate with benzylidene malononitriles, in the cyclopropanation reaction of diethyl bromomalonate and 2-benzylidene-1,3-indandione, and in the Darzens condensation of α-chloroacetophenone with benzaldehyde, maximum enantioselectivities of 39%, 65%, 99%, 56%, and 62%, respectively, were obtained in the presence of the d-mannitol-based macrocycles as the catalysts.

In this contribution, we present new insights and a critical discussion in the optical detection of saxitoxin using fluorophores with crown ethers. Fluorescence enhancement is caused by the reduction of photoinduced electron transfer upon complexation with the analyte. Our attempts to improve this detection method neither did yield a functioning sensor nor were the attempts to reproduce published data in this area successful. Due to the fact that only low concentrations of saxitoxin are available, multiple surrogates were investigated at high concentrations. However, no turn on response was observed. Moreover, a fluorescent decomposition product of saxitoxin that forms under UV light was discovered which was in our opinion misinterpreted as a sensor response by previous publications. Graphical abstract Electronic supplementary material The online version of this article (10.1007/s00706-017-2074-x) contains supplementary material, which is available to authorized users.

[EN] Herein, we report the synthesis, X-ray crystal structure and photophysical studies of six new 8-amino-BODIPY derivatives containing crown or azo-crown ether moieties. The influence of steric hindrance, caused by the crown ether, on the planarity of the BODIPY core and its relationship with the fluorescent properties has been established. H-1 NMR spectroscopic studies were undertaken to clarify the changes in fluorescence observed in the presence of Zn-II., We thank the Spanish Government, Fondos Europeos para el Desarrollo Regional (FEDER) (MAT2015-64139-C4-4-R) and the Generalitat Valenciana (PROMETEOII/2014/047) for support. SCSIE (Universitat de Valencia) is gratefully acknowledged for all the equipment employed. NMR spectra were recorded at the U26 facility of ICTS "NANBIOSIS" at the Universitat of Valencia. M. de L. B.-M. thanks Consejo Nacional de Ciencia y Tecnologia (CONACyT, Mexico) for a graduate scholarship. We thank Consejo Nacional de Ciencia y Tecnologia (CONACyT, grants 123732 and 253623) and Cuantico de Mexico (www.cuantico.mx) for kind donation of 8-methylthioBODIPY.

Daphenylline, a novel daphniphyllum alkaloid, boasts a fused and bridging ring system coupled with six stereogenic centers. Here we present a direct and short construction of the ACDE ring system of daphenylline from the known 3-(2-bromophenyl)propanal in 10 steps and 17 % overall yield. The synthesis features an iron(III)-catalyzed aza-Cope-Mannich reaction, a self-terminating 6-exo-trig aryl radical-alkene cyclization and an intramolecular Friedel-Crafts acylation.

Two compounds containing isolated uranyl chromate and polychromate units were synthesized through room-temperature reactions of uranyl nitrate, chromium(VI) oxide, and 18-crown-6/15-crown-5 in aqueous solutions. Uranyl chromate with 18-crown-6 consists of neutral (0)(infinity)[(UO2)(CrO4)(H2O)(3)] units formed by the bidentate character of the edge sharing UrO(5) bipyramid with only CrO4 and organic molecules and no additional crystallization water molecules. Uranyl polychromate with 15-crown-5 is the first inorganic compound in which [CrO4](2-), [Cr2O7](2-), and [Cr3O10](2-) chromate groups are observed simultaneously.

Crown ethers are small, cyclic polyethers that have found wide-spread use in phase-transfer catalysis and, to a certain degree, in protein chemistry. Crown ethers readily bind metallic and organic cations, including positively charged amino acid side chains. We elucidated the crystal structures of several protein-crown ether co-crystals grown in the presence of 18-crown-6. We then employed biophysical methods and molecular dynamics simulations to compare these complexes with the corresponding apoproteins and with similar complexes with ring-shaped low-molecular-weight polyethylene glycols. Our studies show that crown ethers can modify protein surface behavior dramatically by stabilizing either intra- or intermolecular interactions. Consequently, we propose that crown ethers can be used to modulate a wide variety of protein surface behaviors, such as oligomerization, domain–domain interactions, stabilization in organic solvents, and crystallization.

1,8-Dioxyanthracene-based bisarylene crown ethers, composed of ethylene glycol chains and aromatic moieties, have been synthesized. Complexation studies revealed that these crown ethers could form 1:1 complexes with methyl viologen dication (N,N′-dimethyl-4,4′-bipyridinium dication; MV2+) in a mixed solvent of CDCl3 and CD3CN (1:1 v/v) with association constants in a range of (1.2 ± 0.1) × 103 M–1 to (1.6 ± 0.2) × 104 M–1. The structure of the complex and the strength of the π-donor/π-acceptor interactions between the 1,8-dioxyanthracene planes and the pyridinium rings of MV2+ are highly dependent on the length of the polyether chains of the ethers. Structural analysis showed that the tetraethylene glycol-derived bis-1,8-dioxyanthracene-based crown ether 9 forms a U-shaped host-guest complex with MV2+ by inserting the coplanar pyridinium rings of MV2+ between the two parallel oriented 1,8-dioxyanthracene units of 9, which is driven predominantly by π-donor/π-acceptor interactions. The pentaethylene glycol-derived bis-1,8-dioxyanthracene-based crown ether 10, however, adopts a crescent-shaped conformation in complex 10⊃MV2+ with the MV2+ guest being encapsulated by the polyether chains, propelled mainly by the hydrogen-bonding interactions between the hydrogen atoms of MV2+ and the oxygen atoms of the polyether chains of 10. Similarly, the hexaethylene glycol-derived bis-1,8-dioxyanthracene-based crown ether 11 forms a complex with MV2+. However, only weak π-donor/π-acceptor interactions between the aromatic groups of the mixed bisarylene crown ethers 12 and 13, and MV2+ were observed, and construction of tetracationic cyclophane [CBPQT4+] and crown ether 13 based [2]catenane 15 was achieved through supramolecular interactions between the [CBPQT4+] ring and naphtho unit in the crown ether.

Two novel macroporous silica-polymer-calixcrown hybrid supramolecular recognition materials, 25,27-bis(n-octyloxy)calix[4]arene-crown-6 (BnOCalix[4]C6)/SiO2-P and 25,27-bis(i-octyloxy)calix[4]arene-crown-6 (BiOCalix[4]C6)/SiO2-P were synthesized by in situ polymerization and impregnation techniques. The obtained materials were characterized by scanning electron microscope (SEM), particle size distribution, nitrogen adsorption-desorption isotherms, thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, Si-29 solid-state NMR, and powder X-ray diffraction (XRD). The adsorption of some typical fission and non-fission products Na(I), K(I), Rb(I), Cs(I), Sr(II), Ba(II), La(III), Y(III), Pd(II), Ru(III), Zr(IV), and Mo(VI) onto BnOCalix[4]C6/SiO2-P and BiOCalix[4]C6/SiO2-P in HNO3 solution was investigated. The bleeding of the materials in HNO3 solution was evaluated by analysis of total organic carbon (TOC). BnOCalix[4]C6/SiO2-P and BiOCalix[4]C6/SiO2-P exhibited excellent adsorption ability and high selectivity for Cs(I) over all the other tested metals. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.

Two series of lanthanide metal-organic frameworks, [KLn3(FDCA)5(H2O)5]·solvent (1Ln) (Ln = La 1, Ce 2, Pr 3), [K4Ln8(FDCA)14(H2O)30]·2(H2FDCA)·DMAC·10(H2O) (2Ln) (Ln = Eu 4, Gd 5, Tb 6, Dy 7, Er 8, DMAC = N,N-dimethylacetamide), have been prepared by solvothermal reactions of 2,5-furandicarboxylic acid (H2FDCA) and KNO3 with the corresponding lanthanide nitrate. X-ray crystal structure analyses show that 1Ln possesses a 3D network based on the “16-crown-6-like” secondary building unit (SBU), whereas 2Ln exhibits a 1D framework with a “23-crown-9-like” SBU. The structural investigation unambiguously demonstrated that the lanthanide contraction affects the formation of 1Ln and 2Ln. Meanwhile, the solid-state photoluminescent properties of 4 and 6 were also investigated at room temperature and the luminescence intensity of 4 is sensitive to small molecules.

Mono-, di- tri-, and tetrathiadibenzo[24]crown-8-ethers with eight oxygen or sulfur atoms within the 24-menbered ring have been synthesized by using 1,2-benzenedithiol and 2-hydroxythiophenol as the starting materials. The thia[24]crown ethers form [2]pseudorotaxanes with dibenzylammonium salts, the association constants of which vary depending on the numbers and positions of the sulfur and oxygen atoms. The [2]pseudorotaxane of 1,4-dithiadibenzo[24]crown-8-ether (1,4-DTC) was converted into its Pd complex [PdCl2(1,4-DTC)] by the addition of [PdCl2(cod)] (cod = 1,5-cyclooctadiene), accompanied by the liberation of dibenzylammonium. Subsequent addition of PPh3 to the mixture led to regeneration of the [2]pseudorotaxane. A [2]pseudorotaxane composed of 1,4-DTC and dialkylammonium with two vinyl groups at both ends of the axis component underwent a cross-metathesis reaction with an acrylate ester to form the corresponding [2]rotaxane with an interlocked structure.

A new type of dynamic covalent macrocycle with self-promoted supramolecular gelation behavior is developed. Under oxidative conditions, the dithiol compound containing a diamide alkyl linker with an odd number (7) of carbon chain and an appended crown ether shows a remarkable gelation ability in acetonitrile, without any template molecules. Due to the existence of crown ethers and disulfide bonds, the obtained gel shows a multiple stimuli-responsiveness behavior. The mechanical properties and reversibility of the gel are investigated. Computational modeling suggests that the peripheral chain for diamide hydrogen bonding is responsible for the gelation process.

Five dioxynaphthalene[38]-crown-10 (DNP38C10) macrocycles bearing one, two, three, or four allyl moieties have been synthesized and their ability to spontaneously self-assemble with methyl viologen to form [2]pseudorotaxanes has been evaluated. Association constants between methyl viologen and several of the allyl-functionalized DNP38C10 macrocycles are found to be comparable to that of methyl viologen and unfunctionalized DNP38C10, however, the enthalpic and entropic factors that underlie overall binding free energy vary systematically with increasing allyl substitution. These variations are explained through a combination of solution phase and solid-state analysis of the macrocycles and their complexes. The utility of endowing DNP38C10 macrocycles with allyl moieties is further demonstrated by the ease with which they can be functionalized through thiol-ene click chemistry.

In research activities toward new electrolyte materials for energy devices, the new tetracyanidoborates [Li(C8H16O4)2][B(CN)4] (1), [Na(C8H16O4)2][B(CN)4] (2), [Li(C10H20O5)][B(CN)4] (3), and [Na(C10H20O5)][B(CN)4] (4), which contain lithium and sodium metal cations coordinated by macrocyclic polyether molecules, were synthesized and characterized. Their structures were determined by single-crystal X-ray diffraction measurements. Compounds 1 and 2 form orthorhombic crystals built up from isolated ion pairs. The alkaline metal cation is coordinated by eight oxygen atoms of two 12-crown-4 (12Cr4) crown ether molecules. Compounds 3 and 4 crystallize in the monoclinic crystal system and are constructed from salt chains that extend in one direction. The Na compound has double rows of approximately face-to-face oriented complex cations, which are bridged by two CN groups of each tetracyanidoborate anion. The Li compound contains single strands. In both cases, each anion has two coordinated and two uncoordinated CN groups. The different bonding situations in all four compounds are characterized by IR, Raman, and NMR spectroscopy. Electrochemical spectroscopy was performed to obtain the overall specific conductivity of 1 and 3. Furthermore, differential scanning calorimetry (DSC) measurements revealed melting points below 200 °C and decomposition temperatures above 230 °C.

A novel quinoline-substituted crown ether has been synthesized as a receptor for ion pairs and its binding behavior was investigated in various solvents. The binding of ion pairs in [D6]DMSO and in mixed [D6]DMSO/CD3CN/CDCl3 solvents was studied and the results revealed positive cooperativity effects. As a novel solubilizing agent, the crown ether can extract halide salts into organic media, especially chloride salts. ESI MS provided evidence for the formation of salt-receptor complexes. A recycling experiment showed that the receptor can solubilize salts and can be recovered. This process can be performed as a cycle. This study validates the idea that a straightforward combination of a common anion receptor and a well-studied cation complexation moiety enables the formation of ion-pair receptors and solubilizers of salts in organic solvents.

Herein, we report the synthesis of two phenylaza-[18]crown-6 lariat ethers with a coumarin fluorophore (1 and 2) and we reveal that compound 1 is an excellent probe for K(+) ions under simulated physiological conditions. The presence of a 2-methoxyethoxy lariat group at the ortho position of the anilino moiety is crucial to the substantially increased stability of compounds 1 and 2 over their lariat-free phenylaza-[18]crown-6 ether analogues. Probe 1 shows a high K(+)/Na(+) selectivity and a 2.5-fold fluorescence enhancement was observed in the presence of 100 mM K(+) ions. A fluorescent membrane sensor, which was prepared by incorporating probe 1 into a hydrogel, showed a fully reversible response, a response time of 150 s, and a signal change of 7.8% per 1 mM K(+) within the range 1-10 mM K(+). The membrane was easily fabricated (only a single sensing layer on a solid polyester support), yet no leaching was observed. Moreover, compound 1 rapidly permeated into cells, was cytocompatible, and was suitable for the fluorescent imaging of K(+) ions on both the extracellular and intracellular levels.

Trimeric oligonorbornenes with hammock-like crown ether pendants 3b and 3c were selectively synthesized by cascade metathetical cyclopolymerization upon treatment with the first generation Grubbs catalyst. These crown-ether-containing oligonorbornenes are impregnated in egg yolk phosphatidylcholine (EYPC) liposome as an artificial ion channel. The efficiency of the sodium ion transport properties has been examined. Oligomer 3c having a polar hydroxy end group exhibits the highest transport efficiency, which is comparable with the best efficiencies reported in literature. The orientation of the crown ether moieties in these oligomers may be critical for the ion transport properties.

A π-conjugated phenylaza-15-crown-5-triazol-substituted coumarin fluoroionophore 1 was synthesized by copper(I)-catalyzed Huisgen alkyne-azide 1,3-dipolar cycloaddition (CuAAC "click" reaction). 1 can display selective fluorescence enhancement toward Fe3+ over Hg2+, Cr3+ and the other metal ions in aqueous solution. In sharp contrast, the fluorescence behavior between Fe3+ and Hg2+ is completely reversed in EtOH. That is, Hg2+ gives the largest fluorescence enhancement over Cr3+, Fe3+ and the other metal ions.

Four cone p-tert-butylcalix[4]arene-1,3-monothiacrown-5 ligands each with two N-(X)sulfonyl carbamoylmethoxy side arms are synthesized for comparison with analogs having only oxygen heteroatoms in the crown ether ring. Solvent extractions of hard alkali metal and alkaline earth metal cations, intermediate Pb2+, and soft Hg2+ from aqueous solutions into chloroform by these ligands are utilized to probe the effects of sulfur replacement in the crown ether ring on metal ion complexation.

Double-armed crown ether aldehydes (1–3) were synthesized from the reaction of 2 equiv salicylaldehyde, 4-hydroxy-3-methoxybenzaldehyde (vanillin), and 3-hydroxy-4-methoxybenzaldehyde (iso-vanillin) with 4′,5′-bis(bromomethyl)benzo-15-crown-5. New crown ethers imine compounds (4–9) were synthesized by the condensation of corresponding crown ether aldehydes (1–3) with 4-amino-1,2-dihydro-1,5-dimethyl-2-phenyl-3H-pyrazole-3-one and 2-furan-2-yl-methylamine. Sodium complexes (1a–9a) of the crown compounds form crystalline 1:1 (Na+:ligand) stoichiometries and were also synthesized. The structures of the crown ether aldehydes (1–3), imine compounds (4–9), and complexes (1a–9a) were confirmed on the basis of elemental analyses, IR, 1H and 13C NMR, and mass spectrometry. © 2013 Wiley Periodicals, Inc. Heteroatom Chem 24:100–109, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.21070

A new synthetic route to enantiopure P-stereogenic benzodiphosphacrowns using a P-stereogenic secondary bisphosphine as the key building block is reported. Syntheses of the enantiomer and P-stereogenic crowns with various ring structures, as well as deboranation of the crown compounds and subsequent reaction with a platinum complex, are described.

2,3,3',4,4'-Penta-O-benzylsucrose was converted into the corresponding diaminoalcohol which was used as a key building block in the synthesis of the analogues of aza-crown ethers and bis-lactams.

In 2008, we reported a new class of pillar-shaped macrocyclic hosts, known as "pillar[n]arenes". Today, pillar[n]arenes are recognized as key players in supramolecular chemistry because of their facile synthesis, unique pillar shape, versatile functionality, interesting host-guest properties, and original supramolecular assembly characteristics, which have resulted in numerous electrochemical and biomedical material applications. In this Review, we have provided historical background to macrocyclic chemistry, followed by a detailed discussion of the fundamental properties of pillar[n]arenes, including their synthesis, structure, and host-guest properties. Furthermore, we have discussed the applications of pillar[n]arenes to materials science, as well as their applications in supramolecular chemistry, in terms of their fundamental properties. Finally, we have described the future perspectives of pillar[n]arene chemistry. We hope that this Review will provide a useful reference for researchers working in the field and inspire discoveries concerning pillar[n]arene chemistry.

We report a combined approach that introduces the use of 4-aminobenzo-15-crown-5 (4AB15C5) for the detection of ferric(III) ions by colorimetric, ultraviolet (UV)-visible light absorption, fluorescence, and live-cell imaging techniques along with density functional theory (DFT) calculations. We have found that 4AB15C5 is sensitive and selective for binding ferric(III) ions in aqueous solutions. DFT calculations using the polarizable continuum model have been used to explain the strong binding of the ferric ion by 4AB15C5 in aqueous solutions. The detection limit in the fluorescence quenching measurements was found to be as low as 50 μM for the ferric ion with a determined Stern-Volmer constant of 1.52 × 10

The natural KcsA K+ channel, one of the best-characterized biological pore structures, conducts K+ cations at high rates while excluding Na+ cations. The KcsA K+ channel is of primordial inspiration for the design of artificial channels. Important progress in improving conduction activity and K+ /Na+ selectivity has been achieved with artificial ion-channel systems. However, simple artificial systems exhibiting K+ /Na+ selectivity and mimicking the biofunctions of the KcsA K+ channel are unknown. Herein, an artificial ion channel formed by H-bonded stacks of squalyl crown ethers, in which K+ conduction is highly preferred to Na+ conduction, is reported. The K+ -channel behavior is interpreted as arising from discreet stacks of dimers resulting in the formation of oligomeric channels, in which transport of cations occurs through macrocycles mixed with dimeric carriers undergoing dynamic exchange within the bilayer membrane. The present highly K+ -selective macrocyclic channel can be regarded as a biomimetic alternative to the KcsA channel.

International audience; The reverse anomeric effect (RAE) was investigated in different mannosyl [2]rotaxane molecular shuttle isomers that contain dibenzo-24-crown-8 (DB24C8) as the macrocycle, and anilinium and pyridinium amide as molecular stations. The switching on or off of the RAE was possible depending on both the pyridinium amide motif and the localization of the DB24C8 along the thread. The 1C4 mannopyranosyl chair-like conformation was observed in all the non-interlocked molecules because the anomeric carbon of the mannose is linked to the positively charged nitrogen of the pyridinium unit. In the protonated rotaxanes, the 1C4 chair conformation of the mannose end remains because the DB24C8 resides around the best anilinium station, which is located at the other end of the axle. Upon deprotonation of the anilinium, the DB24C8 shuttles with a large-amplitude motion toward the pyridinium amide stations, where it interacts in a different fashion depending on the pyridinium motif. In one molecular shuttle, the RAE could be switched on or off with control at one end of the encircled thread upon protonation/deprotonation of the other end, through shuttling of the DB24C8.

International audience; The efficient synthesis and very easy isolation of dibenzo[24]crown-8-based [2]pseudorotaxane building blocks that contain an active ester motif at the extremity of the encircled molecular axle and an ammonium moiety as a template for the dibenzo[24]crown-8 is reported. The active ester acts both as a semistopper for the [2]pseudorotaxane species and as an extensible extremity. Among the various investigated active ester moieties, those that allow for the slippage process are given particular focus because this strategy produces fewer side products. Extension of the selected N-hydroxysuccinimide ester based pseudorotaxane building block by using either a mono- or a diamino compound, both containing a triazolium moiety, is also described. These provide a pH-dependent two-station [2]rotaxane molecular machine and a palindromic [3]rotaxane molecular machine, respectively. Molecular machinery on both interlocked compounds through variation of pH was studied and characterized by means of NMR spectroscopy.

A series of new benzo-15-crown-5 derivatives (1–6) containing formyl and imine groups were prepared. New formyl crown ethers (1 and 2) were prepared by reaction of 4′,5′-bis(bromomethyl)benzo-15-crown-5 with 2-hydroxy-3-methoxybenzaldehyde (o-vanillin) and 2-hydroxy-5-methoxybenzaldehyde in the presence of NaOH. New Schiff bases (3–6) were synthesized by the condensation of corresponding aldehydes with 1,3-diaminopropane and 1,4-diaminobutane. Sodium and potassium complexes (1a–6a and 1b–6b) of the crown compounds forming crystalline complexes of 1:1 (Na+:ligand) and 1:2 (K+:ligand) stoichiometries were also synthesized. The structures of the aldehydes 1 and 2, imines 3–6 and complexes (1a–3a and 1b–3b) were confirmed on the basis of elemental analyses, IR, 1H- and 13C-NMR, and mass spectroscopy.

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.

New enantiopure crown ethers containing either an ethyl diarylphosphinate moiety [(S,S)-4 to (S,S)-7] or a proton-ionizable diarylphosphinic acid unit [(S,S)-8 to (S,S)-11] have been synthesized. Electronic circular dichroism (ECD) studies on the complexation of these new enantiopure crown ethers with the enantiomers of α-(1-naphthyl)ethylammonium perchlorate (1-NEA) and with α-(2-naphthyl)ethylammonium perchlorate (2-NEA) were also carried out. These studies showed appreciable enantiomeric recognition with heterochiral [(S,S)-crown ether plus either (R)-1- or (R)-2-NEA] preference. Theoretical calculations found three significant intermolecular hydrogen bonds in the complexes of (S,S)-9. Furthermore, preference for heterochiral complexes was also observed, in good agreement with ECD results. Complex formation constants were determined by NMR titration for four selected crown ether/NEA pairs.

A new, selective, straightforward and general method for preparation of highly functionalized coronands or spiro derivatives bearing 1,2-dihydroxyacetophenone unit, under conventional conditions and ultrasonic irradiation, is reported. The reaction setup involves only one step, acylation of an α-chloro-3,4-dihydroxyacetophenone with phthaloyl dichloride derivatives. 1,3- and 1,4-Phthaloyl dichloride derivatives leads to coronands only, while 1,2-phthaloyl dichlorides lead either to coronands or to spiro derivatives. A feasible explanation for the different behavior between conventional and ultrasound methods could be the different reaction mechanism involved in the two procedures: tetrahedral nucleophilic substitution under conventional conditions and radical substitution under ultrasound. Ultrasound induces a remarkable acceleration of the reactions (from days to minutes) and, most significantly, the yields are twice as high. A feasible explanation for the efficiency of the reactions under ultrasonic irradiation is presented.

Herein, we report the synthesis and characterisation of liquid crystalline crown ethers bearing central [15]crown-5, unsymmetric [18]crown-6 and [21]crown-7 with lateral o-terphenyl and triphenylene substituents. Comparison with similar derivatives of [12]crown-4, symmetric [18]crown-6 and [24]crown-8 revealed beneficial effects of symmetry reduction on the mesomorphic properties. Decreasing symmetry led to broader phases and melting points at lower temperatures.