Calix-crowns

Kavallieratos, K., Moyer, B. A., Attenuation of Hofmeister bias in ion-pair extraction by a disulfonamide anion host used in strikingly effective synergistic combination with a calix-crown Cs+ host, Chem. Commun., 1620-1621, 2001. 

Single-element Separation Extraction of Cs + ion is fairly difficult due to the small charge density of the atomic surface. Thus, calix-crowns were preferentially used for the extraction, because they trap Cs + ion not only by coordinating with the crown ring, but also by interaction with the n-electrons of the phenyl rings of the calixarene (382, 383). On the other hand, many reports appeared concerning extraction of Sr2+ from acidic solutions by crown ethers (384). 

Calix-crowns. In France, exploratory studies of calix-crown molecules have been conducted by Dozol et al. (CEA) with the cooperation of ligand synthesis by Ungaro... 

Category Targets Process Extractants Modifier Crown Ether, Calix-Crown Diluent Remarks... 

Sr ARTIST (Sr) 0.2 M TODGA — Crown Ether, Calix-Crown rc-Dodecane Laboratory test... 

Mohapatra, P.K., Ansari, S.A., Sarkar, A., Bhattacharyya, A., Manchanda, V.K. 2006. Evaluation of calix-crown ionophores for selective separation of radio-esium from acidic nuclear waste solution. Anal. Chim. Acta 571 (2) 308-314. 

The first studies performed at Strasbourg University by the picrate extraction method developed by Pedersen reveals a high preference of calix-crowns fixed in the 1,3-alternate conformation for cesium. In contrast to its conformational isomer, di-isopropoxy-calix[4]arene-crown-6 in the cone conformation does not extract cesium (Table 4.4). 

Sachleben et al. observed that for bis(alkoxy)calix[4]arene monocrown ethers, reducing the size of the alkoxy substituent from octyl to allyl increased the cesium extraction by 10%-30% and the cesium-to-potassium selectivity by 20%-40%, with little impact on cesium over sodium selectivity. A standard modeling approach was used to analyze the complementarity of the calix-crown cavity toward potassium and cesium. MM3 optimizations were performed by modifying the K+ and Cs+ complexes, replacing the 1,3-dioxybenzene-substituent with tert-butoxy, methoxy, or hydrogen groups. 

The SF is given as SF = DCs syn//)Cs B, the ratio of DCs obtained under synergistic conditions versus Da obtained for the calix-crown alone. The variable O is the organic-to-aqueous phase volume ratio. The absence of an anion receptor is indicated by subscript/ = 0, and the subscripts init, aq, and org refer to initial, aqueous, and organic. 

Calix-crowns extract cesium from acidic and alkaline solutions with extremely high Cs/Na selectivity.66 71 Because their selectivity is higher, it seems promising to use the calix-crown instead of DB21C7 for extraction of cesium in mixtures with the... 

Luo et al.90 have described yet another approach to reducing the impact of ion exchange in metal ion extraction by neutral extractants in ILs, one which relies on modifying neither the structure of the IL nor the properties of the extractant. Instead, a sacrificial species that transfers in preference to the IL cation upon metal ion extraction (thereby reducing loss of the IL) is added to the IL phase. Ideally, the sacrificial species should exhibit no affinity for the extractant (in order not to interfere with extraction of the metal ion of interest) and be more hydrophilic than the IL cation (in order to favor its loss to the aqueous phase upon metal ion transfer). Tests with sodium tetraphenylborate indicate that its addition to a solution of a calix-crown ether in [C4mim+][Tf2N ] reduces the loss of the IL induced by cesium extraction by nearly one-quarter with no adverse effect on the efficiency of cesium extraction. 

With the larger Ms(calix) crown (3.127),65 two dynamic processes are observed. The intermolecular association/disassociation equilibrium in which the complex equilibrates with the uncomplexed ligand and free metal cation is slow on the NMR time scale. The complex also exhibits a faster intramolecular vibration of the metal cation from one binding site to another (Scheme 3.26). Compound 3.127 is also interesting because the mechanism of this fast, intramolecular cation shuttling process may have important implications on the analogous movement of metal cations through transmembrane ion channels (Section 2.2). 

Among more complex macrocycles, Li et al. [47-52] reported the preparation and characterization of stationary phases incorporating calixarenes or calix-crowns bonded to silica. With individual columns, high selectivity was observed in the separation of alkylated aromatics, aromatic carboxylic acids, sulfonamides, nucleosides, and water-soluble vitamins. In other work, Sokoliess et al. [53] have characterized calixarene- and resorcinarene-bonded stationary phases similar to those described in the previous section of this chapter. And Huai et al. [54] used an end-capped p-tert-butyl-calix[4]arene-bonded silica phase for HPLC separation of a number of organic compounds. Resorcinarenes have also found application in GC. [55-57] Recently, exotic macrocycles have been used in capillary electrochromatography, as reported by Gong et al. [58]... 

Hill, C., Dozol, J. F., Lamare, V., Rouquette, H., Eymard, S., Toumois, B., Vicens, J., Asfari, Z., Bressot, C., Ungaro, R., Casnati, A. Nuclear Waste Treatment by Means of Supported Liquid Membranes Containing Calix-Crown Compounds, J. Inch Phenom. Mol. Recogn. Chem. 19 (1994), 399-408. 

Calix-crowns, calix-cryptands and extended networks.361... 

Baek, S. H., et al. (2004), Surface plasmon resonance imaging analysis of hexahistidine-tagged protein on the gold thin film coated with a calix crown derivative, Biotechnol. Bioprocess. Eng., 9,143-146. 

Literally thousands of heteromacrocycles are now known. Many additional compounds have been prepared during the past decade but, for the most part, the synthetic approaches are traditional. Recent work has often focused on developing sidearmed receptor molecules (see Section 14.14.7.1), mixed receptor systems such as calix-crowns (Section 14.14.7.2), and oligomers or polymers containing crown residues. 

Until recently, the role of slow rates of cation release in LM transport was unclear. From U NMR studies, it is known that the complexes can be kinetically stable [65, 66] and, as a consequence, decomplexation rates can be very slow. Influence of slow rates of alkah metal cations release was raised in transport through a BLM [58,64,67-69]. Recently, at cation transport experiments with different calix crown ether derivatives [42,70], was proven that the rate of decomplexation can be rate controlling in the transport through SLMs. 

A unique assembly of a crystalline hybrid supramolecular salt was achieved by reaction of 2,4-bis (3-pyridylmethyl)oxy -(l,3)-p-bu -calix[4]-crown-6 (33), hexadecafluoro-l,8-diidooctane and Csl (2(X) 4951). In its solid state, the cesium ion of the supercation was encapsulated inside the cavity created by the crown ether loop, the picolyl and inverted phenyl moieties, whereas the two iodide ions of the superanion, formed a discrete five component aggregate held together by hydrogen and halogen bonds. Similar adduct existed in solution. A combination of this calix-crown 33 and octafluoro-l,4-diiodobutane acted as an effective binary host for the selective extraction of Csl from aqueous to fluonous phase. 

Fig. 3 Molecular structure of 1,2-his-calix crown ether (A) 1-3 alternate calix crown ether (B) and 1.3-his-calix crown ether (C).

The construction of calix-crown molecules is achieved by grafting ethylene glycol chains in a loop at two of the phenolic functions (Fig. 3A). 

Raut, D.R., Evaluation of two calix-crown-6 ligands for the recovery of radio cesium from nuclear waste solutions Solvent extraction and liquid membrane studies, J. Membr. Sci. 429, 197, 2013. 

Macrocyclic and macromolecular carriers are compounds such as crown ethers, ionizable lariat ethers, calixarenes, calix crowns, and cyclodextrins. Table 27.3 provides examples of such carries as well as the target chemical species. 

Figure 14 Conformational interconversion upon caesium or sodium binding by calix-crown-6 (17).

The extensive studies on the binding-free energies of the alkali metal ion complexes for the different stereoisomers, cone, partial cone, and 1,3-alternate, revealed a strong dependence of the binding efficiency upon calixarene conformation, although all the calix-crown-5 are selective... 

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