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Articoli di riviste sul tema "Crown ethers"

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Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 31 luglio 2024

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1

Mao, Hua, John B. Thorne, Jennifer S. Pharr e Robert E. Gawley. "Effect of crown ether ring size on binding and fluorescence response to saxitoxin in anthracylmethyl monoazacrown ether chemosensors". Canadian Journal of Chemistry 84, n. 10 (1 ottobre 2006): 1273–79. http://dx.doi.org/10.1139/v06-093.

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Convenient macrocyclization synthetic routes for the preparation of different-sized monoaza anthracylmethyl crown ether chemosensors (15-crown-5, 18-crown-6, 21-crown-7, 24-crown-8, and 27-crown-9) are described. Evaluation of these crowns as chemosensors for saxitoxin revealed that the larger crowns have moderately higher binding constants, with the 27-crown-9 chemosensor having the largest binding constant (2.29 × 105 (mol/L)–1). Fluorescence enhancements of 100% were observed at saxitoxin concentrations of 5 µmol/L, which is close to the detection limit in mouse bioassay.Key words: anthracene, crown ethers, saxitoxin, paralytic shellfish poison (PSP), binding constants; chemosensors.

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2

Pranowo, Harno Dwi, e Chairil Anwar. "INTERACTION BETWEEN Li⁺ CATION WITH CROWN ETHERS OF Bz15C5, DBz16C5 AND DBz18C6: MOLECULAR MODELING BASE ON MNDO/d SEMIEMPIRICAL METHOD". Indonesian Journal of Chemistry 3, n. 1 (7 giugno 2010): 55–66. http://dx.doi.org/10.22146/ijc.21906.

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

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3

Fronczek, Frank R., Richard D. Gandour, Thomas M. Fyles, Philippa J. Hocking, Susan J. McDermid e P. Daniel Wotton. "Polycarboxylate crown ethers from meso-tartaric acid". Canadian Journal of Chemistry 69, n. 1 (1 gennaio 1991): 12–19. http://dx.doi.org/10.1139/v91-003.

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The synthesis of crown ethers derived from meso-tartaric acid was investigated. The sodium salt of the bis(dimethylamide) of meso-tartaric acid reacted with diethylene glycol ditosylate to give a mixture of 18-crown-6 tetraamide and 27-crown-9 hexaamide crown ethers. The 2R,3S,11S,12R 18-crown-6 isomer crystallized in triclinic space group [Formula: see text] (a = 7.557(2), b = 8.866(2), c = 10.4133(13) Å, α = 94.13(2), β = 95.86(2), γ = 99.26(2)°, R = 0.040 for 2090 observed of 3129 unique reflections). The structures of the remaining products were then assigned from the NMR spectra. The solution conformations of the amide crown ethers were examined by NMR, and provide a rationale for the product distribution obtained. One of the 18-crown-6 isomers and a mixture of the two 27-crown-9 isomers were hydrolyzed to the respective crown ether carboxylic acids, and the stability constants for complexation of cations were determined by potentiometric titration. The meso tetra- and hexacarboxylates are remarkably nonselective and inefficient cation complexing agents, compared to related crown ethers from R,R-(+)-tartaric acid, due to the unfavorable conformational control exerted by the tartaro units. Key words: crown ether synthesis, complexation, crown ether conformation, meso-tartaric acid, crystal structure.

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4

Lu, Zhongyuan, Benjamin A. Jackson e Evangelos Miliordos. "Ab Initio Calculations on the Ground and Excited Electronic States of Thorium–Ammonia, Thorium–Aza-Crown, and Thorium–Crown Ether Complexes". Molecules 28, n. 12 (12 giugno 2023): 4712. http://dx.doi.org/10.3390/molecules28124712.

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Positively charged metal–ammonia complexes are known to host peripheral, diffuse electrons around their molecular skeleton. The resulting neutral species form materials known as expanded or liquid metals. Alkali, alkaline earth, and transition metals have been investigated previously in experimental and theoretical studies of both the gas and condensed phase. This work is the first ab initio exploration of an f-block metal–ammonia complex. The ground and excited states are calculated for Th0–3+ complexes with ammonia, crown ethers, and aza-crown ethers. For Th3+ complexes, the one valence electron Th populates the metal’s 6d or 7f orbitals. For Th0–2+, the additional electrons prefer occupation of the outer s- and p-type orbitals of the complex, except Th(NH3)10, which uniquely places all four electrons in outer orbitals of the complex. Although thorium coordinates up to ten ammonia ligands, octa-coordinated complexes are more stable. Crown ether complexes have a similar electronic spectrum to ammonia complexes, but excitations of electrons in the outer orbitals of the complex are higher in energy. Aza-crown ethers disfavor the orbitals perpendicular to the crowns, attributed to the N-H bonds pointing along the plane of the crowns.

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5

Zimnicka, Magdalena M. "Crown ethers as shift reagents in peptide epimer differentiation –conclusions from examination of ac-(H)FRW-NH2 petide sequences". International Journal for Ion Mobility Spectrometry 23, n. 2 (ottobre 2020): 177–88. http://dx.doi.org/10.1007/s12127-020-00271-2.

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Abstract Crown ethers with different ring sizes and substituents (18-crown-6, dibenzo-18-crown-6, dicyclohexano-18-crown-6, a chiral tetracarboxylic acid-18-crown-6 ether, dibenzo-21-crown-7, and dibenzo-30-crown-10) were evaluated as shift reagents to differentiate epimeric model peptides (tri-and tetrapeptides) using ion mobility mass spectrometry (IM-MS). The stable associates of peptide epimers with crown ethers were detected and examined using traveling-wave ion mobility time-of-flight mass spectrometer (Synapt G2-S HDMS) equipped with an electrospray ion source. The overall decrease of the epimer separation upon crown ether complexation was observed. The increase of the effectiveness of the microsolvation of a basic moiety - guanidine or ammonium group in the peptide had no or little effect on the epimer discrimination. Any increase of the epimer separation, which referred to the specific association mode between crown substituents and a given peptide sequence, was drastically reduced for the longer peptide sequence (tetrapeptide). The obtained results suggest that the application of the crown ethers as shift reagents in ion mobility mass spectrometry is limited to the formation of complexes differing in stoichiometry rather than it refers to a specific coordination mode between a crown ether and a peptide molecule.

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6

Szemenyei, Balázs, Balázs Novotny, Sarolta Zsolnai, Zsombor Miskolczy, László Biczók, Attila Takács, László Kollár, László Drahos, Ildikó Móczár e Péter Huszthy. "Push or Pull for a Better Selectivity? A Study on the Electronic Effects of Substituents of the Pyridine Ring on the Enantiomeric Recognition of Chiral Pyridino-18-Crown-6 Ethers". Symmetry 12, n. 11 (30 ottobre 2020): 1795. http://dx.doi.org/10.3390/sym12111795.

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Seven dimethyl-substituted optically active pyridino-18-crown-6 ethers containing various substituents at position 4 of the pyridine ring were studied with regards to the electron-donating and -withdrawing effects of substituents on enantiomeric recognition. In order to compile this set of compounds, we prepared four novel pyridino-18-crown-6 ethers, including an intermediate of a new synthetic route for a formerly reported crown ether. The discriminating ability of these pyridino-crown ethers with C2-symmetry toward the enantiomers of protonated primary amines was examined by isothermal titration calorimetry.

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7

Anantanarayan, Ashok, e Thomas M. Fyles. "Polycarboxylate diaza crown ethers derived from R,R-(+)-tartaric acid: synthesis and complexation of metal ions". Canadian Journal of Chemistry 68, n. 8 (1 agosto 1990): 1338–51. http://dx.doi.org/10.1139/v90-206.

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The synthesis and complexation properties of polycarboxylate diaza crown ethers based on R,R-(+)-tartaric acid are described. Cesium carbonate mediated macrocyclization of a bis-tosylamide precursor with a bis-tosylate precursor provided the protected crown ethers. Photochemical deprotection of the tosylamides and hydrolysis of the carboxamides yielded dicarboxylic and tetracarboxylic acid derivatives of 1,10-diaza-18-crown-6. N-Methylenecarboxylate (N-acetate) derivatives were prepared by N-alkylation with bromoacetic acid. The synthetic and purification procedures developed provide samples of the ligands in a metal-free form. Acidity and stability constants for complexation of alkali metal, alkaline earth, late- and post-transition metal cations were determined by potentiometric titration. The ligands form complexes which show enhancement of stability by charge–charge and chelate interaction with the carboxylates. In comparison with crown ether polycarboxylates these aza crown ethers showed a selectivity for softer metal ions relative to alkali and alkaline earth metal ions. N-Methylenecarboxylate chelate ligands were found to bind almost all types of metal ions, due to a highly co-operative array of charge–charge, chelate and crown ether interactions. Keywords: aza crown ether synthesis, tartaric acid, potentiometric titration, cation complexation, aminocarboxylate complexone.

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8

Esseffar, M'hamed, Mohamed El Mouhtadi, José-Luis M. Abboud, José Elguero e Daniel Liotard. "Étude théorique (AM1) de l'affinité protonique des polyéthers cycliques (éthers couronnes) et non cycliques (glymes)". Canadian Journal of Chemistry 69, n. 12 (1 dicembre 1991): 1970–75. http://dx.doi.org/10.1139/v91-283.

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Semi-empirical calculations at the AM1 level have been used to study the proton affinity (PA) of polyether compounds (dioxane, glymes, and crown ethers). The calculated values, although systematically lower than the experimental ones, are linearly correlated with eight experimental PA's (r = 0.993). Taking into account the considerable conformational changes that take place upon protonation, the result is highly satisfactory and provides an estimate of proton affinity for 9-ether-crown-3 (206.5 kcal mol−1) and glyme-5 (231.1 kcal mol−1). Moreover, this work provides a rationale for the fact that, for the same number of oxygen atoms, glymes are more basic than crown ethers. For the crown ethers, the proton affinity depends on angular strain in the base and on intramolecular hydrogen bonds in the cation. Key words: protonation, reactivity, glymes, crown ethers, coordination.

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9

Oh, Young-Ho, Ju Gyeong Jeong, Dong Wook Kim e Sungyul Lee. "Nucleophilic Reactions Using Alkali Metal Fluorides Activated by Crown Ethers and Derivatives". Catalysts 13, n. 3 (27 febbraio 2023): 479. http://dx.doi.org/10.3390/catal13030479.

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We review crown ether-facilitated nucleophilic reactions using metal salts, presenting the studies using kinetic measurements and quantum chemical methods. We focus on the mechanistic features, specifically on the contact ion-pair (CIP) mechanism of metal salts for nucleophilic processes promoted by crown ethers and derivatives. Experimental verification of the CIP form of the metal salt CsF complexed with [18-Crown-6] by H-NMR spectroscopy is described. The use of chiral crown ethers and derivatives for enantioselective nucleophilic processes is also discussed.

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10

Inoue, Yoshihisa, Hiroya Harino, Toshiyo Nakazato, Noriaki Koseki e Tadao Hakushi. "Unsaturated crown ethers. 3. Syntheses of stilbeno crown ethers". Journal of Organic Chemistry 50, n. 25 (dicembre 1985): 5151–56. http://dx.doi.org/10.1021/jo00225a035.

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11

KOSCHEEVA, A. M., A. M. KOSCHEEV, A. V. RODIN, V. L. VIDANOV e A. V. ANANIEV. "EXTRACTION OF CESIUM AND STRONTIUM FROM NITRIC ACID SOLUTIONS, USING CROWN-ETHERS IN HEAVY DILUENTS". Chemical Engineering 25, n. 2 (2024): 60–66. http://dx.doi.org/10.31044/1684-5811-2024-25-2-60-66.

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The extraction ability of crown-ethers has been studied with respect to cesium and strontium from nitric acid solutions in heavyweight polar organic solvents: chloroform; 1,2-dichloroethane; bis(2-chloroethyl)ether; nitrobenzene; 1,1,7-trihydrododecafluoroheptyl alcohol. Using bis(2-chloroethyl)ether as a new polar solvent in the extraction processes of dibenzo21-crown-7 and 4,4' (5')-ditretbutyldibenzo-18-crown-6, rather high distribution coefficients of cesium are achieved (DCs) from solutions with a nitric acid concentration of 1-5 mol / dm3. In the extraction of dicyclohexyl-18-crown-6 strontium, the highest DSr values were obtained, using chlorine-substituted hydrocarbons and bis(2-chloroethyl)ether with an extraction maximum of 1-3 mol / dm3 HNO3, depending on the diluent used. Extraction systems based on selective crown-ethers in a solvent mixture for the joint extraction of cesium and strontium from chemically complex nitric acid solutions are proposed.

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12

Kurmanaliev, M. K., N. A. Bektenov e K. A. Sadykov. "SELECTIVE SORBENTS BASED ON DIAMINODICYCLOHEXYLCROWN ETHERS". Chemical Journal of Kazakhstan, n. 1 (30 marzo 2023): 54–63. http://dx.doi.org/10.51580/2023-1.2710-1185.06.

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Macromolecules with crown ether groups are a fundamentally new type of sorbents whose active centers are ligands that retain electrical neutrality in the process of simultaneous binding of cations, anions, or organic compounds. The purpose of this work is to create new selective sorbents based on diaminodicyclohexylcrown ethers and to study their complexing properties with respect to alkali metal ions. Methodology. To study the composition and properties of the products of the synthesis of crown ether-containing sorbents, chemical and physicochemical methods of analysis were used: infrared spectroscopy, atomic absorption spectrophotometry. Results and discussion. Chemical grafting of cycloaliphatic crown ethers onto a macroporous chloromethylated copolymer of styrene and divinylbenzene has been carried out. Under the chosen conditions, when using diaminodicyclohexyl-18-crown-6, polycrown ethers were obtained with a content of crown ether grains of 1.42 mmol/g, when using diaminodicyclohexyl-24-crown-8, the content of macrocyclic groups was 1.24 mmol/g. The extraction of alkali metals under static conditions by grafted sorbents based on various macrocycles has been studied. The high values of the distribution coefficients of alkali metals (Na+, K+, Cs+) by the synthesized sorbents in an acidic medium are shown. The following selectivity series were found for the sorbent with diaminodicyclohexyl-18-crown-6 fragments: K+ ˃ Cs + ˃ Na+, and for the sorbent with diaminodicyclohexyl-24-crown-8 fragments: Cs+ ˃ K+ ˃ Na+ metals. Conclusion. The efficiency of extracting metal ions from aqueous solutions containing Crown esters is affected by the presence of amino groups. It is known that the amino group promotes the formation of a polymer that swells in water. It was noted that the use of sorbents based on polymers that swell in water when metal salts are removed from the aqueous medium leads to an increase in the sorption capacity of sorbents by facilitating the access of metal ions in water to the active areas of the immobilized sorbent.

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13

Dutton, Philip J., Thomas M. Fyles e Susan J. McDermid. "Synthesis and metal ion complexation behavior of polycarboxylate 18-crown-6 ethers derived from tartaric acid". Canadian Journal of Chemistry 66, n. 5 (1 maggio 1988): 1097–108. http://dx.doi.org/10.1139/v88-181.

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The metal ion complexation behavior of four 18-crown-6 ethers derived from (+)- and meso-tartaric acid is examined. Preparations of a meso-crown ether diacid and of a crown ether hexacid from three units of (+)-tartaric acid are described. Acidity constants and stability constants for complexation of metal cations in aqueous solution were determined by potentiometric titration. The complexes are substantially stabilized by favourable electrostatic interactions and are of similar stability to complexes of cryptands and EDTA. The complexation behavior of the series can be rationalized in terms of electrostatic interactions, direct coordination of the cations by at least one carboxylate from the crown ether periphery, and rigidification of the ligands as the anionic charge increases. Distributions of charge influence the relative stability of isomeric complexes. Highly charged polycarboxylate crown ethers are effective, but relatively unselective, cation complexing agents for a range of cations. The complexes are stable to pH 3 and the ligands can be used as simultaneous pH and metal ion buffers.

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14

Yuan, Liu, Jun Zhu, Shaofei Wu e Chunyan Chi. "Enhanced emission by stacking of crown ether side chains in a 2D covalent organic framework". Chemical Communications 58, n. 9 (2022): 1302–5. http://dx.doi.org/10.1039/d1cc03409j.

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15

Tsybyshev, V. P., V. A. Livshits, B. B. Meshkov, O. A. Fedorova, S. P. Gromov e M. V. Alfimov. "Photochromic crown ethers". Russian Chemical Bulletin 46, n. 7 (luglio 1997): 1239–44. http://dx.doi.org/10.1007/bf02495919.

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16

Li, YuanQiang, Thies Thiemann, Tsuyoshi Sawada e Masashi Tashiro. "Novel crown ethers by oxidative cycloaddition of thiopheno crown ethers". Journal of the Chemical Society, Perkin Transactions 1, n. 16 (1994): 2323. http://dx.doi.org/10.1039/p19940002323.

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17

Rouser, Mason A., e Harry W. Gibson. "Desymmetrization of disubstituted aromatic crown ethers via intramolecular Cannizzaro reactions". New Journal of Chemistry 43, n. 43 (2019): 16801–5. http://dx.doi.org/10.1039/c9nj04679h.

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Ba⁺⁺ templated Cannizzaro reactions convert symmetrical aromatic crown ether dialdehydes of various types [dibenzo and bis(meta-phenylene)] and sizes (20–32 atom rings) to acid–alcohol functionalized crown ethers in 70–98% yields.

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18

Omichi, Yamashita, Okura, Ikutomo, Ueki, Seko e Kakuchi. "Surface Engineering of Fluoropolymer Films via the Attachment of Crown Ether Derivatives Based on the Combination of Radiation-Induced Graft Polymerization and the Kabachnik–Fields Reaction". Polymers 11, n. 8 (12 agosto 2019): 1337. http://dx.doi.org/10.3390/polym11081337.

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In this manuscript, we present the successful attachment of crown ether moieties onto fluoropolymer surfaces, via the combination of radiation-induced graft polymerization and a subsequent surface Kabachnik–Fields three-component reaction. The obtained crown ether-tethered fluoropolymer films exhibited an ammonium cation capturing ability, owing to the host–guest interactions (i.e., hydrogen bonding) between the surface-anchored crown ethers and the guest ammonium cations.

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19

Gibson, Harry W., e Sang-Hun Lee. "42-crown-14-based [2]catenane". Canadian Journal of Chemistry 78, n. 3 (1 marzo 2000): 347–55. http://dx.doi.org/10.1139/v00-017.

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A compound isolated from a synthesis directed toward 42-crown-14 (42C14) has been purified and characterized by means of IR, HPLC, NMR, MS, and DSC techniques. Its infrared spectrum contains no OH, tosylate, or unsaturated unit signals. The HPLC retention time of the compound differs from that of "42C14" and other crown ethers examined. The chemical shifts of the singlets in the 1H and 13C NMR spectra differ from those of poly(ethylene oxide)s (PEOs), and crown ethers. The FAB mass spectra contain signals attributable to a compound with twice the mass of 42C14 and the fragmentation pattern is consistent with [2]catenane 9 based on interlocked 42C14 units, because the next major signals generally correspond to 42C14 and its adducts. The DSC results showed that the compound, a colorless wax at room temperature, was amorphous with a glass transition temperature which was 80° higher than those of aliphatic crown ethers, which are crystalline compounds with melting points >40°C. Considering the high yield of the compound (8% in the reaction mixture as determined by NMR, 1.7% isolated), it is believed that sodium cation-crown ether-linear ether complexation was involved in templating its formation. Evidence for such complexation was also observed in the FAB MS.Key words: catenanes, crown compounds, macrocycles, template synthesis, rotaxanes.

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20

McLain, Stephan J. "Organometallic crown ethers. 2. Syntheses of phosphino aza crown ether ligands". Inorganic Chemistry 25, n. 18 (agosto 1986): 3124–27. http://dx.doi.org/10.1021/ic00238a005.

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21

Moghimi, Abolghasem, Majid Faal Rastegar e Mehdi Ghandi. "A novel crown ether generation containing the pyrilium heteroaromatic cation Synthesis, characterization, and solid-phase 13C NMR". Canadian Journal of Chemistry 82, n. 12 (1 dicembre 2004): 1716–24. http://dx.doi.org/10.1139/v04-144.

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The synthesis and structural characterization of two members, 5 and 6, of a novel generation of crown ethers containing the pyrilium cation are reported. These two compounds contain two and three benzo-9-crown-3 (B9C3) units, respectively, connected to the 2 and 6 or 2, 4, and 6 positions of a central pyrilium cation. The crown ethers 5 and 6 were obtained from the condensation reaction of appropriate aldehydes and methyl ketones in the presence of POCl3. A variety of physicochemical methods including electrospray mass spectroscopy, solution 1H and 13C NMR, and solid-phase 13C NMR were applied for structural characterization. The 1H and 13C NMR studies indicate rapid rotation of the B9C3 unit about the CC bond that connects the two units to each other. The solid-phase 13C NMR spectra of these two crown ethers reveal that there are deviations from planarity for the two phenyl rings attached at the 2 and 6 positions of the central pyrilium cation.Key words: crown ether, pyrilium, solid-phase NMR, crownpyrilium, heteroaromatic.

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22

Ströbele, Markus, e H. Jtirgen Meyer. "Synthesen, Kristallstrukturen und magnetische Eigenschaften von [Li(12-Krone-4)2][Li(12-Krone-4)(OH2)]2[Nb6Cl18], [Li(15-Krone-5)2(OH2)]3[Nb6Cl18] und [(18-Krone-6)2(O2H5)]3[Nb6Cl18] / Syntheses, Crystal Structures and Magnetic Behaviour of [Li(12-Krone-4)2][Li(12-Krone-4)(OH2)]2[Nb6Cl18], [Li(15-Krone-5)2(OH2)]3[Nb6Cl18] and [(18-Krone-6)2(O2H5)]3[Nb6Cl18]". Zeitschrift für Naturforschung B 56, n. 10 (1 ottobre 2001): 1025–34. http://dx.doi.org/10.1515/znb-2001-1011.

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The title compounds were prepared through reactions of Li2Nb6Cl16 with the corresponding crown ethers in acetone. All three compounds were obtained as dark brown crystals. Their structures were solved with the means of single-crystal X-ray diffraction.[Li(12-crown-4)2][Li(12-crown-4)(OH2)]2[Nb6Cl18]: space group P21/n, Z =2, a = 1320.4(1), b = 1879.1(1), c = 1321.7(1) pm, ß = 92.515(6)°, R1 = 0.0297 (I>2σ(I)). The crystal structure contains Li+ sandwiched by two 12-crown-4-ethers plus Li+ coordinated by one 12-crown-4- ether and one water molecule.[Li(15-crown-5)2(OH2)]3[Nb6Cl18]: space group R3̅, Z = 3, a = b = 2081.7(1), c = 1991.7(1) pm, R1 = 0.0395 (I > 2σ(I)). In the crystal structure Li+ and one water molecule are sandwiched by two 15-crown-5-ethers.[(18-crown-6)2(O2H5)]3[Nb6Cl18]: space group P1̅, Z = 1 ,a = 1405.1(1), b = 1461.1(2), c = 1492.2(2) pm; α = 98.80(1)°, ß = 98.15(1)°, γ = 97.41(1)°, R1 = 0.0538 (I > 2σ(I)). H5O2+ was found in the structure refinement sandwiched between two 18-crown-6-ethers.All compounds reported contain [Nb6Cl18] clusters with Nb-Nb distances between 299 and 301 pm. The paramagnetic behaviour expected for [Nb6Cl18]3- in all three compounds was confirmed by magnetic measurements.

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Ostaszewski, Ryszard. "The synthesis of anthracene crown ethers derived from benzo-crown ethers". Tetrahedron 54, n. 24 (giugno 1998): 6897–902. http://dx.doi.org/10.1016/s0040-4020(98)00370-6.

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24

Frańska, Magdalena, e Anna Michalak. "Gas-phase relative stabilities of Tl+-crown ether complexes and Rb+-crown ether complexes". European Journal of Mass Spectrometry 24, n. 3 (10 gennaio 2018): 279–88. http://dx.doi.org/10.1177/1469066717752794.

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The gas-phase stabilities of Tl+-crown ether complexes and Rb+-crown ether complexes were studied using the electrospray ionization-collision-induced dissociation-tandem mass spectrometry. Tl+ and Rb+ have identical ionic radii, thus a comparison of the properties of the crown ether complexes with these two cations seems to be justified. The selected crown ethers were 12C4 (it has a cavity smaller than the cation radius), 18C6 (it has a cavity of size similar to the cation radius), 24C8 (it has a cavity greater than the cation radius) and their conjugates. It has been found that the crown ether complexes of stoichiometry 1:1 with Tl+ are more or equally stable in the gas phase than the crown ether complexes with Rb+. However, 2:1 complexes with Tl+ are less stable than the complexes with Rb+.

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25

Guo, Kai, Sitong Liu, Haoming Tu, Zhikun Wang, Liang Chen, Haiqing Lin, Maosheng Miao, Jing Xu e Wei Liu. "Crown ethers in hydrogenated graphene". Physical Chemistry Chemical Physics 23, n. 34 (2021): 18983–89. http://dx.doi.org/10.1039/d1cp03069h.

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Graphane could serve as an ideal platform to rigidify the highly flexible crown ethers, which will greatly improve the binding strength and selectivity of crown ethers with metal cations and open up new applications for crown ethers and graphane.

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26

Chou, Ming-Seng, e Jeng-Shong Shih. "Preparation and application of 4′-carboxybenzo-15-crown-5, a drift-type crown ether phase transfer catalyst". Canadian Journal of Chemistry 72, n. 7 (1 luglio 1994): 1614–20. http://dx.doi.org/10.1139/v94-202.

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Abstract (sommario):

A new "drift-type" crown ether phase transfer catalyst, 4′-carboxybenzo-15-crown-5 adsorbed on poly(styrene/divinylbenzene)-NR2 resin, was synthesized and applied to catalyze the oxidation of benzhydrol with NaMNO4 as an oxidant. Before the reaction, the drift-type crown ether catalyst was adsorbed on the resin with ion-pair (resin-NR2H+−O2C-monobenzo-15-crown-5) formation. During the reaction period the crown ether catalyst was released from the resin into the reaction solution as a homogeneous catalyst by adjusting the acidity of the solution to 10−1 M HCl to destroy the ion pair between the catalyst and the resin. After the reaction, the crown ether catalyst could be readsorbed on the resin by adjusting the concentration of HCl to 10−5 M and could be readily recovered by filtration. The catalyst, 4′-carboxybenzo- 15-crown-5, was found to be a more effective catalyst than other crown ethers, such as 15-crown-5, 18-crown-6, monobenzo-15-crown-5, and dibenzo-18-crown-5.

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27

Buchanan, G. W., A. Moghimi e C. Bensimon. "Novel O-C-C-O and C-O-C-C stereochemistry in crown ether analogs. X-ray crystal structure and NMR studies of dibenzo-20-crown-6". Canadian Journal of Chemistry 73, n. 1 (1 gennaio 1995): 100–105. http://dx.doi.org/10.1139/v95-015.

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Abstract (sommario):

The X-ray crystal structure of the title material indicates that the molecule possesses a pseudo-centre of inversion. A pair of O-C-C-O bonds have a trans conformation in contrast to normal gauche stereochemistry for such units in crown ethers. For the C-O-C-C networks, which are normally transoid in crown ethers, all four such units involving methylene carbons of the 20-membered ring exhibit unusual geometries. Two units possess gauche conformations and the other two have torsion angles near 120°. Solution 1H and 13C NMR spectra have been recorded as a function of temperature and 13C solid state spectra are included. Keywords: crown ether, solid state conformation.

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28

Buchanan, G. W., M. Z. Khan, J. A. Ripmeester, J. W. Bovenkamp e A. Rodrigue. "13C nuclear magnetic resonance spectra in the solid state of 18-crown-6•NaNCS•H2O, some dicyclohexyl-18-crown-6 ethers, and their complexes with phenoxides and phenol". Canadian Journal of Chemistry 65, n. 11 (1 novembre 1987): 2564–67. http://dx.doi.org/10.1139/v87-426.

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Abstract (sommario):

High resolution 13C CPMAS spectra for three configurationally isomeric dicyclohexyl-18-crown-6 ethers and three complexes derived therefrom are presented. Spectra are consistent with conformationally locked crown ether structures at 298 K. Data are discussed in terms of the symmetry properties of the macrocycles and stereochemical effects on 13C chemical shifts in the solid phase. For the complex of 18-crown-6 with NaSCN and H2O, a single line is observed at 298 K. Temperature reduction removes the chemical shift averaging as the different torsional angles of the solid crown ether undergo distortions that become slow on the nuclear magnetic resonance timescale.

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29

Dickert, Franz L., e Michael W. Vonend. "Konkurrierende Koordination von Kronenethern, Perchloratanionen und Lösungsmittelmolekülen am Co(II)-Ion — Eine Leitfähigkeits-und NMR-Studie in Nitromethan / Competitive Coordination of Crown Ethers, Perchlorate Anions and Solvent Molecules at Co(II)-Ions — A Conductivity and NMR Study on Nitromethane". Zeitschrift für Naturforschung B 42, n. 1 (1 gennaio 1987): 42–46. http://dx.doi.org/10.1515/znb-1987-0109.

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Abstract (sommario):

Abstract The 1:1 complexes between Co(II) and the crown ethers dibenzo[24]crown-8, dibenzo[18]-crown-6 and [18]crown-6 show a molar conductivity in nitromethane which indicates coordination of even perchlorate anions. The substitution of this anion by solvent molecules can be monitored by conductometric titrations. This procedure reveals that dibenzo[24]crown-8 and [18]crown-6 is a potent five dentate ligand whereas dibenzo[18]crown-6 strongly coordinates only via three donor atoms. The mixed complexes with crown ether and methanol show strong outer-sphere associa-tion with the Perchlorate anions, which can be confirmed by investigations with [15]crown-5 complexes.

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30

Brandt, N. N., A. Yu Chikishev, A. A. Mankova, M. M. Nazarov, I. K. Sakodynskaya e A. P. Shkurinov. "THz and IR Spectroscopy of Molecular Systems That Simulate Function-Related Structural Changes of Proteins". Spectroscopy: An International Journal 27 (2012): 429–32. http://dx.doi.org/10.1155/2012/745136.

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Abstract (sommario):

The activity of enzymes in organic solvents substantially increases in the presence of crown ethers. Tris(hydroxymethyl)aminomethane (tris) is chosen as a model compound to simulate the interaction of surface amino groups of proteins with crown ether. The methods of FTIR and time-domain THz spectroscopy are used to study the interaction of tris with 18-crown-6. The THz spectra of the complexes are measured for the first time.

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31

Lee, Wonjae, Eunjung Bang, Ji-Hye Yun, Man-Jeong Paik e Weontae Lee. "Enantiodiscrimination Using a Chiral Crown Ether as a Chiral Solvating Agent Using NMR Spectroscopy". Natural Product Communications 14, n. 5 (1 maggio 2019): 1934578X1984919. http://dx.doi.org/10.1177/1934578x19849191.

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Abstract (sommario):

For enantiomer separation of a variety of chiral compounds, a number of chiral selectors have been developed and applied. Among these chiral selectors are chiral crown ethers, a class of synthetic polyether molecules that bind protonated chiral primary amines with high selectivity. This article focuses on enantiodiscrimination using (18-crown-6)-2,3,11,12-tetracarboxylic acid as a crown ether-type chiral solvating agent for nuclear magnetic resonance spectroscopic method in several chirotechnologies.

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32

Nehlig, Annick, Ge´rard Kaufmann, Zouhair Asfari e Jacques Vicens. "Fluorenylidene-diphenyl-crown-ethers". Tetrahedron Letters 40, n. 32 (agosto 1999): 5865–68. http://dx.doi.org/10.1016/s0040-4039(99)01155-7.

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33

Truter, M. R. "Crown ethers and analogs". Endeavour 14, n. 4 (gennaio 1990): 203. http://dx.doi.org/10.1016/0160-9327(90)90059-z.

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34

Kakuchi, Toyoji, Katsutoshi Aoki, Osamu Haba e Kazuaki Yokota. "Polymeric chiral crown ethers". Polymer Bulletin 31, n. 1 (luglio 1993): 37–42. http://dx.doi.org/10.1007/bf00298761.

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35

Chaloner, Penny A. "Crown ethers and analogues". Journal of Organometallic Chemistry 396, n. 1 (ottobre 1990): C26. http://dx.doi.org/10.1016/0022-328x(90)85207-f.

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36

Miethchen, Ralf, e Volker Fehring. "Carbohydrate-Based Crown Ethers". Liebigs Annalen 1997, n. 3 (marzo 1997): 553–61. http://dx.doi.org/10.1002/jlac.199719970317.

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37

AMABILINO, D. B., J. A. PREECE e J. F. STODDART. "ChemInform Abstract: Crown Ethers". ChemInform 28, n. 15 (4 agosto 2010): no. http://dx.doi.org/10.1002/chin.199715297.

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38

BRADSHAW, J. S., R. M. IZATT, A. V. BORDUNOV, C. Y. ZHU e J. K. HATHAWAY. "ChemInform Abstract: Crown Ethers". ChemInform 28, n. 7 (4 agosto 2010): no. http://dx.doi.org/10.1002/chin.199707294.

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39

Hausner, Sven H., Cynthia A. F. Striley, Jeanette A. Krause-Bauer e Hans Zimmer. "Dibenzotetraaza Crown Ethers: A New Family of Crown Ethers Based ono-Phenylenediamine†". Journal of Organic Chemistry 70, n. 15 (luglio 2005): 5804–17. http://dx.doi.org/10.1021/jo050281z.

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40

LI, Y. Q., T. THIEMANN, T. SAWADA e M. TASHIRO. "ChemInform Abstract: Novel Crown Ethers by Oxidative Cycloaddition of Thiopheno Crown Ethers." ChemInform 26, n. 4 (18 agosto 2010): no. http://dx.doi.org/10.1002/chin.199504202.

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41

Bujor, Alexandru, Victorita Tecuceanu, Anamaria Hanganu e Petre Ionita. "Synthesis and Structural Analysis of a Nitrobenzofurazan Derivative of Dibenzo-18-Crown-6 Ether". Chemistry 4, n. 4 (9 dicembre 2022): 1696–701. http://dx.doi.org/10.3390/chemistry4040110.

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Abstract (sommario):

Nitrobenzofurazan derivatives are well known for their fluorescence, whilst crown ethers are known for their complexing capacity toward cationic species. In this study, we present the synthesis and structural characterization of a new derivative containing both nitrobenzofurazan moieties and a crown ether core. The new compound was obtained from dibenzo-18-crown-6 ether, which was first nitrated, reduced to the corresponding amine, and subsequently derivatized with NBD. Structural analyses performed by IR, NMR, UV–Vis, and MS confirmed its structure and physico-chemical behavior toward the complexation of alkaline cations.

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42

Bey, Alexandra, Oliver Dreyer e Volker Abetz. "Thermodynamic analysis of alkali metal complex formation of polymer-bonded crown ether". Physical Chemistry Chemical Physics 19, n. 24 (2017): 15924–32. http://dx.doi.org/10.1039/c7cp02651j.

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43

Yahmin, Yahmin, Harno Dwi Pranowo e Ria Armunanto. "AB INITIO INVESTIGATION OF 12-CROWN-4 AND BENZO-12-CROWN-4 COMPLEXES WITH Li⁺, Na⁺, K⁺, Zn²⁺, Cd²⁺, AND Hg²⁺". Indonesian Journal of Chemistry 10, n. 1 (21 giugno 2010): 106–9. http://dx.doi.org/10.22146/ijc.21488.

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Abstract (sommario):

The structure and binding energies of 12-crown-4 and benzo-12-crown-4 complexes with Li+, Na+, K+, Zn2+, Cd2+, and Hg2+were investigated with ab initio calculations using Hartree-Fock approximation and second-order perturbation theory. The basis set used in this study is lanl2mb. The structure optimization of cation-crown ether complexes was evaluated at HF/lanl2mb level of theory and interaction energy of the corresponding complexes was calculated at MP2/lanl2mb level of theory (MP2/lanl2mb//HF/lanl2mb). Interactions of the crown ethers and the cations were discussed in term of the structure parameter of crown ether. The binding energies of the complexes show that all complex formed from transition metal cations is more stable than the complexes formed from alkali metal cations. Keywords: 12-crown-4, benzo-12-crown-4, alkali metals, transition metals

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44

Akopyan, T. R., e E. G. Paronikyan. "Chemistry of crown ethers. Synthesis of new crown ethers containing a pyridazine ring". Chemistry of Heterocyclic Compounds 33, n. 12 (dicembre 1997): 1466–68. http://dx.doi.org/10.1007/bf02291651.

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45

Derwish, Ghazi A. W., Salman R. Salman e Sabri M. H. Al-Marsoumi. "Molecular complexes of crown ethers. part 2: Complexes between crown ethers and ? acceptors". Journal of Inclusion Phenomena and Molecular Recognition in Chemistry 20, n. 2 (1995): 123–29. http://dx.doi.org/10.1007/bf00709336.

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46

Salman, SalmanR, e SabriM Al-Marsumi. "Molecular complexes of crown ethers—Part 1. Complexes between crown ethers and iodine". Spectrochimica Acta Part A: Molecular Spectroscopy 49, n. 3 (marzo 1993): 435. http://dx.doi.org/10.1016/0584-8539(93)80144-y.

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47

OSTASZEWSKI, R. "ChemInform Abstract: The Synthesis of Anthracene Crown Ethers Derived from Benzo-Crown Ethers." ChemInform 29, n. 40 (19 giugno 2010): no. http://dx.doi.org/10.1002/chin.199840174.

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48

Bulut, M., e Ç. L. Erk. "The synthesis of novel crown ethers, part ix, 3-phenyl chromenone-crown ethers". Journal of Heterocyclic Chemistry 38, n. 6 (novembre 2001): 1291–95. http://dx.doi.org/10.1002/jhet.5570380608.

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49

Eliasson, Bertil, Kerstin M. Larsson e Jozef Kowalewski. "Multinuclear NMR relaxation studies of crown ethers and alkali cation crown ether complexes". Journal of Physical Chemistry 89, n. 2 (gennaio 1985): 258–61. http://dx.doi.org/10.1021/j100248a016.

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50

Pugia, Michael J., Anna Czech, Bronislaw P. Czech e Richard A. Bartsch. "Phase-transfer catalysis by polymer-supported crown ethers and soluble crown ether analogs". Journal of Organic Chemistry 51, n. 15 (luglio 1986): 2945–48. http://dx.doi.org/10.1021/jo00365a016.

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