Crown ether-calixarenes

After the separation of the actinides from the high-level waste, it is desirable to remove certain other fission products from the nuclear wastes. Some Cs and Sr are low-charged cations that react well with macro-cyclic ligands (e.g., crown ethers, calixarenes). Research to synthesize and investigate the properties of macrocyclic ligands for application in nuclear waste treatment has been an active effort internationally. Some of the results obtained are discussed in section 12.7. 

Supramolecules containing metal-polypyridine units, especially the Ru(dpp)-based dendrimers, could be used as electron reservoirs or components of molecular-electronic devices. Supramolecules in which an electroactive M(N,N) group is attached to a receptor capable of molecular recognition (crown ethers, calixarenes, cryptands etc.) can work as electrochemical sensors. Electrochemical recognition of cations as well as anions has been reported [33-35, 257, 263]. 

The two calix[4]arenes, 24 and 26, are examples of useful derivatives the former binds lanthanides to form luminescent complexes, the latter, prepared from compound 25, is water soluble and crystallizes in a variety of forms, from laminates to nanospheres. Other derivatives are to be found in the literature. Simple derivatives, such as the O-alkyl compounds, are used as a basis for upper rim functionalization treatment of these compounds with nitric acid replaces the upper f-butyl groups with nitrates. Nitrocalixarenes can be reduced to the corresponding amines to generate a platform for further extension of the cavity and have been used to bind metals or small molecules. Oxa- and azacalix[3]arenes represent crown ether-calixarene hybrids and have binding modes reminiscent of both classes of molecules. Many alternative upper rim substituents can be introduced and, in the case of the azacalixarenes, the /V-substituent can easily be varied. 

The organic liquids used for liquid membranes are as follows dichlorometh-ane, chloroform, kerosene, chlorobenzene, n-octane, n-decane, n-dodecane, and -tetradecane. The most popular carriers are crown ethers, calixarenes, phospho-roorganic compounds (e.g., D2EHPA and CYANEX 302), hydroxyoximes (e.g., LIX 65N and SME 529), and amines (e.g., ALAMINA 336 and tri-n-octylamine). In general, liquid membranes are used mostly to decrease the radiotoxicity of the liquid waste, but not to reduce its volume. In radioactive waste management, liquid membranes are first applied to ranove Sr and Cs from acidic or alkaline solutions (Kocherginsky et al. 2002 Happel Streng et al. 2003). 

A potential for large ring and cavity formation extends to many P-containing organic molecules, in addition to the inorganic phosphates discussed above. These compounds include phosphate derivatives of fashionable structures such as crown ethers, calixarenes, carceplexes, catenanes, rotaxanes, self-assembly molecules and so on, and varieties which are discussed in Chapter 10, such as cyclo-dextrins, phosphosaccharides, phosphoproteins and nucleic acids. Phosphorus analogues of cyclo-polypyridyls and porphyrins are discussed in Chapters 7 and 8. 

Wlakowiak and Kozlowski " recently reviewed the application of macrocycle carriers including crown ethers, calixarenes, calixcrowns, and CDs in liquid membrane processes. The role of macrocyclic ligands as ion carriers for cations such as alkali and alkaline metals, and heavy metals such as Zn ", Cd +, Hg + and Pb " " was summarized. Mutihac reviewed the calixarenes as membrane... 

Usually, receptors designed for ion-pair complexation are molecules comprising weU-known anion-binding motifs, for example, Lewis-acidic centers, and familiar cationbinding motifs, such as crown ethers, calixarenes. The distance occurring between these sites classifies receptors as follows ... 

Macrocycles play an important role in the development of supramolecular chemistry. Based on the traditional macrocycles such as crown ethers, calixarenes, cyclodextrins, and cucurbiturils, a great many supramolecular polymers as well as their applications have been reported. Because pillar-arenes have only had 6 years of development (from 2008), the research on pillararene-based supramolecular polymers is at a preliminary stage. However, all of the efforts made and aehievements that have been reached suggest that pillararenes as well as pillararene-based supramoleeular polymers will have a bright future. 

Numerous examples of artificial channels have been reported since the pioneering work of Tabushi using tetrachained cyclodextrin as a model. Of these examples, the macrocycles, such as crown ethers, calixarenes, cyclodextrins, and cucurbiturils, play an important role. The macrocycles provide not only the platforms for construction of whole channels but also the functional sites necessary to achieve transport selectivity and efficiency. From this viewpoint, pillararenes, new macrocycles with unique structural features, may also act as a platform for building such channels, which will give the channels new functions. This hypothesis has been systematically explored by us. 

Crownophanes, crown ether-calixarenes, and polyepoxyannulenes Comparison of the efficiencies of various low-valent titanium species showed that the metal exerts a strong template effect in the synthesis of crownophanes such as 95 [130] (Figure 6.17). Compound 96 exhibits the shortest and most rigid bridging moiety in the class of stilbenophane crown ethers [131, 132]. A series of crown ether calix[4]-... 

Crownophanes, crown ether-calixarenes, and polyepox annulenes ... 

In this chapter selected examples of metal ion separations with polymeric macrocycles such as crown ethers, calixarenes, resorcinarenes, calixcrowns and cyclodextrins, reported in recent literature, are presented. Particularly, the use of those polymers in separation processes such as ion flotation, solvent extraction as well as transport across liquid and polymer membranes is shown. First, selected examples of crown ether polymers variety cross linked as metal ion carriers are described, then selectivity species by donor sites bonding and coordination are characterized. 

Macrocyclic ligands such as crown ethers, calixarenes, resorcinarenes and calixcrowns are interested organic compounds, which are important in fundamental and applied chemistry [1,2], These compounds can be used as ion receptors for selective removal of metal ions from aqueous solutions in ion exchange processes, such as solvent extraction, ion flotation and transport through liquid membranes [3]. 

The well known complexing properties of macrocyclic compounds towards metal ions have led to their incorporation into polymeric matrices. Polymer-supported crown ethers have many advantages, such as easy handling and recoverability when used for the removal of the toxic metal ions from the environment. Crown ether-, calixarene-, calixcrown- and cyclodextrin- based polymers have been recently receiving attention as the new polymers and may be processed into materials suitable as the extractant (solvent extraction), collector (ion flotation) or the ion carrier (transport across liquid membranes or ion selective electrodes). 

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