Use Of Crown Ethers Research Articles

Review of advanced methods for treating radioactive contaminated water

The accidental release of large quantities of radionuclide after a nuclear accident tends to contaminate the groundwater system or rivers and lakes by the transfer of the main radionuclides such as Cesium 137, Strontium 90 or Cobalt 60, Ruthenium 106 and others (including transuranic radionuclides, such as: 239-Pu, 240-Pu, 241-Am...). The aim of this paper is to review the possible solutions for the removal of these contaminants from large quantities of water. i) The use of crown ethers for the selective removal of Strontium 90 such as the dicyclohexyl 18-crown 6 which is able to remove with 90% of efficiency the Strontium. ii) The use of zeolithes for the removal of Cesium 137. On larger scale the use of electromagnetic filtration technology is able to process in a relatively short time large quantities of water by using a seeding system of resin coated metallic magnetic particles to enhance the filtering efficiency under cold conditions. Examples of water of efficiencies and results obtained on loops at a fairly large scale will be given in this paper, these examples show rather high efficiency of removal even at low concentration of contaminants (a few ppb: part per billion). Examples of water treatment concepts will be also given for treatment of contaminated surface water and to treat large groundwater applications. Major applications could be implemented on various sites namely in Russia (Karatchai Lake) or in Belarus and Ukraine. The magnetic filtration is not a new concept but with the use of various selective adsorbing treatment particles, this concept has been proven so effective that dissolved metals in process water have been reduced to level in the very low ppb range.

Synthesis of F−-containing LTA-type GaPO4 in the presence of crown ethers as organic templates

The use of crown ethers as templating agents in the system Ga2O3-P2O5-HF-H2O was investigated. The LTA-type gallophosphate could be obtained in the presence of the K+ 18-crown-6 ether complex and with aza-crown ethers (Kryptofix 22 and Kryptofix 222). These crown ethers are occluded in the structure (8 molecules per unit cell). The products were characterized by elemental analysis, SEM, XRD and solid-state NMR spectroscopy.

Separation of enantiomers and isomers of amino compounds by capillary electrophoresis and high-performance liquid chromatography utilizing crown ethers

Separation of enantiomers and isomers of a wide variety of primary amines by capillary electrophoresis (CE) was investigated employing charged and uncharged crown ethers. Enantiomer separation of primary amines by CE was successful through the addition of a chiral crown ether, 18-crown-6 tetracarboxylic acid (18C6H 4). Thirteen out of 17 enantiomers tested were separated by CE with 18C6H 4. Low pH values (pH 1.9–2.1) and relatively high Tris concentration (20 m M) were effective for the fast enantiomer separation. Enantiomer separation of the same primary amines was also investigated by high-performance liquid chromatography (HPLC) with a chiral Crownpak CR(+) column, although different chiral crown ether moieties were employed in CE and HPLC. Other than enantiomers, separation of positional isomers of aromatic amino compounds such as aminophenols, aminocresols was investigated by both CE with three kinds of 18-membered crown ethers and HPLC with a Crownpak CR(+) column. The use of crown ethers for the separation of amino compounds is discussed in viewpoint of practical applications. The optical purity testing of amino compounds is also demonstrated.

The Use of Crown Ethers in Peptide Chemistry – V. Solid‐phase Synthesis of Peptides by the Fragment Condensation Approach using Crown Ethers as Non‐covalent Protecting Groups

The Use of Crown Ethers in Peptide Chemistry – V. Solid‐phase Synthesis of Peptides by the Fragment Condensation Approach using Crown Ethers as Non‐covalent Protecting Groups

The use of crown ethers in peptide chemistry-V. Solid-phase synthesis of peptides by the fragment condensation approach using crown ethers as non-covalent protecting groups.

We have previously described the conditions by which peptide synthesis by the solid-phase fragment condensation approach can be carried out using crown ethers as non-covalent protection for the N alpha-amino group. Here we demonstrate that the procedure can be extended to large, partially protected peptide fragments possessing free Lys and/or Arg residues. The first step was to ensure that complex formation on the side chain of amino acids was not detrimental to the methodology and exhibited the same solubility and coupling properties as N alpha-complexed peptides. Thus, a model hexapeptide was synthesized using Fmoc chemistry containing Lys and Arg residues, which, when complexed with 18-Crown-6, was readily soluble in DCM and coupled quantitatively to a resin-bound tetrapeptide. Two tripeptides were then prepared, one containing a free Ser residue, the other free Tyr, to examine the possible occurrence of side reactions. After coupling using standard conditions only the former tripeptide exhibited the formation of the O-acylation by-product (5%). Another model hexapeptide containing Lys, Tyr, Ser and Asp protected with a TFA-stable adamantyl group was complexed with 18-Crown-6 and coupled to the resin-bound tetrapeptide with near quantitative yield. Extending the length of the peptide to 21 and 40 residues, which represent sequences Gly52 to Leu72 (21-mer) and Pro33 to Leu72 (40-mer) from Rattus norvegicus chaperonin 10 protein, respectively, resulted in partially protected fragments that were readily soluble in water, thus enabling purification by RP-HPLC. Complexation with 18-Crown-6 gave two highly soluble products that coupled to resin-board tetramer with 68% and 50% coupling efficiencies for the 21-mer and 40-mer, respectively. Treatment with 1% DIEA solutions followed by acidolytic cleavage and purification of the major product confirmed that the correct product has been formed, when analysed by amino acid analysis and ESI-MS. These results served to extend the methodology of non-covalent protection of large partially protected peptide fragments for the stepwise fragment condensation of polypeptides.

Analysis of90Sr in environmental and biological samples by extraction chromatography using a crown ether

The use of crown ethers is a simple and rapid method for the separation and determination of strontium in various samples. After sample dissolution oxalate precipitation was carried out to remove K. Chromatographic separation of strontium from most inactive and radioactive interference was done with a crown ether. The chemical recovery was determined gravimetrically. Radiostrontium was then determined by liquid scintillation counting.

ChemInform Abstract: The Use of Crown Ethers in Peptide Chemistry. Part 4. Solid Phase Synthesis of Peptides Using Peptide Fragments Nα Protected with 18‐Crown‐6.

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Observation of spatially correlated intergrowths of faujasitic polytypes and the pure end members by high-resolution electron microscopy

Controlled intergrowths of cubic and hexagonal phases of faujasitic materials have been synthesized, using mixtures of crown ethers, and studied by HREM. The results reveal that the end-member materials are pure-phases, nearly free of defects and intergrowths such as those observed without the use of crown ethers. Mixed phases form intergrowths, rather than overgrowths, consisting of short blocks of up to 10 unit cells

Synthesis of ZSM-20 using crown ethers

Recent procedures for synthesis of zeolity Y in either cubic or hexagonal forms that make use of crown ethers, as template, are modified using gels containing fluorides. 15 Crown-5 ether gives the cubic and 18 crown-6-ether gives the hexagonal form. By using a synthesis mixture in which both templates are present, intergrowths of the two forms can be produced including material and analogous to ZSM-20 that is typically synthesized in alkaline systems.

Preparation and properties of stat-copoly-(oxyethylene-oxypropylene)-block-poly (oxyethylene): 1. Use of crown ether in the anionic copolymerization of propylene oxide and ethylene oxide

Stat-copoly(oxyethylene-oxypropylene)s were prepared by anionic polymerization initiated by potassium methoxypropanol in the presence of 18-crown-6 ether, and were characterized by g.p.c. and n.m.r. Molecular weight distributions were narrow. Reactivity ratios, determined from composition and from sequence distribution, were r E = 3.1−3.3 and r P = 0.31−0.33, in good agreement with reactivity ratios determined for polymerization without added crown ether. Diblock copolymers with one stat-copoly (oxyethylene-oxypropylene) block and one poly (oxyethylene) block were prepared by sequential polymerization, and were characterized by g.p.c. and n.m.r.

Use of crown ether in the anionic polymerization of propylene oxide—2. Molecular weight and molecular weight distribution

The production of unsaturation by hydrogen abstraction from monomer (transfer reaction) during the polymerization of bulk propylene oxide catalysed by potassium alkoxide in the presence of 18-crown-6 ether was assessed by NMR spectroscopy. Chain transfer constants were measured as a function of the ratio of crown ether to potassium ion ( r − 0–4.5) over a range of temperatures ( T = 20–80°). Conditions were defined for the preparation of monofunctional poly(oxypropylene) of moderate chain length (about 200 P units, M n > 10,000 ) and narrow chain-length distribution ( M w M n ∼ 1.2 ).

Use of crown ether in the anionic polymerization of propylene oxide—3. Preparation and micellization of diblock-copoly(oxypropylene/oxyethylene)

Diblock-copoly(oxypropylene/oxyethylene)s with moderately-long P-blocks (about 200 P units) and narrow block-length distributions were prepared by use of 18-crown-6 ether and the potassium salt of methoxypropanol in the sequential anionic polymerization of bulk propylene oxide at room temperature and ethylene oxide at 40–80°C (melt). The micellization of one of these copolymers, denoted P 200E 560, was studied by a number of techniques: surface tension, gel permeation chromatography, photon correlation spectroscopy, electron microscopy. The quantities obtained (critical micelle concentration, hydrodynamic radius, micelle size distribution) were compared with published results for other diblock and triblock copolymers.

Use of crown ether in the anionic polymerization of propylene oxide—1. Rate of polymerization

The rate of anionic polymerization of bulk propylene oxide catalysed by potassium alkoxide in the presence of 18-crown-6 ether was followed dilatometrically. Rate constants were obtained at 40, 50 and 60° over a range of crown ether concentrations, so allowing calculation of activation energies for polymerization with and without added crown ether. The results were consistent with polymerization by ligand-separated and contact ion-pairs in equilibrium.

ChemInform Abstract: The Use of Crown Ethers in Peptide Chemistry. Part 3. Synthesis of an Enkephalin Derivative Using 18‐Crown‐6 as Non‐Covalent Amino Protecting Group.

ChemInform Abstract: The Use of Crown Ethers in Peptide Chemistry. Part 3. Synthesis of an Enkephalin Derivative Using 18‐Crown‐6 as Non‐Covalent Amino Protecting Group.

The use of crown ethers in peptide chemistry: Part 3 synthesis of an enkephalin derivative using 18-crown-6 as a non-covalent amino protecting group

The efficacy of amino acid protection with crown ethers is demonstrated by the solution synthesis of an enkephalin pentapeptide derivative. Extraction of the organic phase with a KCl solution after each coupling steps is used for the deprotection of the peptide intermediate.

The use of crown ethers as synergistic extraction agents for trivalent lanthanides

Alkylsulfonic acids, such as didodecylnaphthalenesulfonic acid (HDDNS) have been shown to be effective liquid-liquid cation exchangers for trivalent lanthanide elements. Owing to its strong acid character, HDDNS is an effective extractant at low pH values, but shows little ability to separate individual metal ions from each other. In an effort to introduce more selectivity into the extraction of the trivalent lanthanides by HDDNS, a study of the effect of the addition of various crown ethers to the organic phase was carried out. The presence of the crown ethers enhanced the extraction of the light lanthanides, but not the heavy lanthanides. Little relationship between cavity size of the crown ether and the magnitude of the enhancement was observed.

The use of crown ethers in peptide chemistry. Part 2. Syntheses of dipeptide complexes with cyclic polyether 18-crown-6 and their derivatisation with DMSO

As part of a study the aim of which is to use crown compounds as non-covalent protecting groups in peptide synthesis, we have explored the reactivity of 18-crown-6-ether-dipeptide complexes with dicyclohexylcarbodi-imide (DCC) in dimethyl sulphoxide (DMSO). At a reactant concentration of ca. 0.02 mol dm–3 the DCC did not activate the dipeptide, and the N-acylurea derivative slowly formed. At concentrations of ca. 0.2 mol dm–3 the complexes proved to be unstable and reacted with the solvent to form a DMSO-peptide adduct. The reaction mechanism leading to the latter was elucidated and shown to involve an initial acid-catalysed addition of DMSO to DCC. The presence in solution of nucleophiles gave the peptide ester thus indicating DCC-mediated activation of the peptide carboxylic acid group. The results from this study were used to design the conditions necessary for an effective noncovalent protection of the amino group during peptide synthesis.

Use of crown ethers in gas chromatography

Two new kinds of crown ethers, 4,4-dipentadecyl- or 4,3′0dipentadecyldibenzo-30-crown-10 and 3-pentadecylbenzo-15-crown-5, were coated on glass capillary columns and fused-silica capillary columns, and their chromatographic characteristics studied. The polarity, selectivity and stability of the crown ethers were characterized. The rôle of the crown ether ring in separating solutes is also mentioned.

The participation of crown ethers in the initiation of group-transfer polymerisation

The use of crown ethers in conjunction with alkali metal salts, as catalysts in group-transfer polymerization, is discussed.

ChemInform Abstract: The Use of Crown Ethers in Peptide Chemistry. Part 1. Syntheses of Amino Acid Complexes with the Cyclic Polyether 18‐Crown‐6 and Their Oligomerization in Dicyclohexylcarbodiimide‐Containing Solutions.

AbstractThe amino acid complexes (I) and (II) with the cyclic polyether 18‐crown‐6 are prepared with 77‐97% yield.