Crown ethers, incorporation into

Crown ethers and their derivatives have gained attention for their ability to form stable complexes with metal ions. The selective complexing properties of crown ethers towards metal ions have led recently to their incorporation into polymeric matrices. There are three main methods of crown ethers incorporation into polymer matrices. The first method is direct polymerization of the crown ether in a step-growth process, the second one is the polymerization through a chain-growth process, and the third one is post-functionalization of pre-formed polymers. 

Polyphosphazenes bearing crown ethers (12-crown-4,15-crown-5 and 18-crown-6) as single or as mixed substituents with trifluoroethoxy or methoxy-ethoxyethoxy groups were synthesized by Cowie [601,602] and Allcock [484] and their conductivity studied because it was shown that the incorporation of crown ether molecules into a polymer electrolyte could increase their ionic conductivity. In these macromolecules, the crown ether units were linked to the backbone through oxymethylene spacer groups. 

The incorporation of crown ether units into a cobaltocenium receptor has been shown to allow the switchable sensing of anions. Proton NMR titrations of receptor 8 in CD3CN solution gave log K values of 3.1 for chloride and 3.0 for... 

Recently, the novel design of compartmental Schiff bases has led to the incorporation of crown ether moieties into the macrocyclic structure. One such ligand containing an N3O2 Schiff base and a 020 ( = 3 [H2LA] or 4 [H2LB]) crown-ether functionality (see Figure 73) have been used to... 

The 1,3-xylyl trick was also used for the incorporation of phenols into crown ethers. Three classes of phenols [46a]-[46c] have been investigated. They differ by their substituents in the 4-position. In Table 22 the pX a values of different macrocyclic phenols [46a]-[46c] are compared. The data obtained for the phenol-containing crowns [46a] and [46b] show very little evidence for a macrocyclic effect. No extra stabilization of the protonated (acidic) form by a macrocycle of appropriate ring size was found. The acidities of the macrocyclic phenols [46a] and [46b] were independent of the ring size and comparable to non-macrocyclic analogues. However, the azo-substituted crowns [46c] showed a difference of 0.8 pACg units which was not expected from the pAfa values of [46a] and [46b]. TTiis different behaviour of [46c] is not yet understood. 

Some other types of macrocycle compounds have been synthesized using adamantane and its derivatives. Recently, a new class of cyclobisamides has been synthesized using adamantane derivatives, which shows the general profiles of amino acid (serine or cystine)-ether composites. They were shown to be efficient ion transporters (especially for Na+ ions) in the model membranes [159]. Another interesting family of compounds to which adamantane derivatives have been introduced in order to obtain cyclic frameworks is crown ethers [160]. The outstanding feature of these adamantane-bearing crown ethers (which are also called diamond crowns ) is that ot-amino acids can be incorporated into the adamantano-crown backbone [160]. This family of... 

As stated in Section II, the SHG responses to primary cations of ISEs based on several crown ether ionophores could be correlated to the number of primary ion complexes at the phase boundary, which contributed to the membrane potential. We have now incorporated the K+ ionophore bis[(benzo-15-crown-5)-4-methyl]pimelate into 1,2-dichloroethane and nitrobenzene membranes and determined EMF and SHG responses to KCl in presence and absence of ionic sites. 

We recently synthesized several reasonably surface-active crown-ether-based ionophores. This type of ionophore in fact gave Nernstian slopes for corresponding primary ions with its ionophore of one order or less concentrations than the lowest allowable concentrations for Nernstian slopes with conventional counterpart ionophores. Furthermore, the detection limit was relatively improved with increased offset potentials due to the efficient and increased primary ion uptake into the vicinity of the membrane interface by surfactant ionophores selectively located there. These results were again well explained by the derived model essentially based on the Gouy-Chapman theory. Just like other interfacial phenomena, the surface and bulk phase of the ionophore incorporated liquid membrane may naturally be speculated to be more or less different. The SHG results presented here is one of strong evidence indicating that this is in fact true rather than speculation. 

E. Ishow, A. Credi, V. Balzani, F. Spadola, L. Mandolini, A Molecular-level Plug/socket System. Electronic Energy Transfer from a Binaphthyl Unit Incorporated into a Crown Ether to an Anthracenyl Unit Linked to an Ammonium Ion , Chem. Eur. ]. 1999, 5, 984-989. 

In contrast to Bosman et al., who only found metal complexation in the periphery of polypropylene imine) dendrimers, Tomalia and co-workers reported on the incorporation of copper ions into the interior of PAMAM dendrimers judging from EPR and UV/Vis studies [220, 221]. Metal binding in the dendrimer interior has also been observed for dendrimers carrying multiple ligands for metal complexation within their framework such as crown-ethers [222, 223] (Cs(I)-complexes), piperazine [224] (Pd(II)- and Cu(II)-complexes) or triazocyclononane [225] (Cu(II)- and Ni(II)-complexes). In most cases addition of the metal-salt to the dendrimer led to the formation of 1 1 complexes. 

Anionic units have not only been attached to macrocyclic polyethers via flexible arms but have also been incorporated into the cycle itself. Alberts and Cram (1976, 1977) have studied the ion-binding properties of crown ethers containing / -diketone units, such as [72] and [73]. 

In some instances, a long hydrocarbon chain can be attached to an organometallic compound, e.g., ruthenium trisbypyridyl or ferrocene, thus making a new surfactant which can be readily used to form micelles or can be incorporated into conventional micelles (4, 5). In other cases, a long chain crown ether can... 

The chiral 1,2-diols that have been incorporated into crown ether derivatives that cany substituents but have no fused rings associated with the elements of chirality in the macrocycles are listed in Figure 14. We shall now examine some of the ways in which these chiral building blocks have been used. 

In this section, we shall examine the various approaches by which crown compounds that have their chiral elements associated in some way with fused ring systems can be constructed. A selection of the wide and growing range of saturated chiral diols—many of them derived finom readily available carbohydrates—which have been incorporated, as relatively inexpensive sources of chirality, into crown ether derivatives are displayed in Figure IS. It may be noted that the saturated chiral diols rely for their chirality on centers of the classical type (C abcd)—not so the chiral dihydroxy compounds associated with the unsaturated systems listed in Figure 16. These examples reveal that axes and planes of chirality join with less conventional chiral centers (C aaaa) in being sources of chirality in optically active crown ethers. 

Closely related to the synthetic work reported in the previous section is the incorporation (131) of a 2,5-anhydro-3,4Hdi-0-methyl-D-mannitol residue (Figure 15) into the 18-crown-6 derivative d-91. Other derivatives of D-mannitol that have been built into crown ether receptors include l,4 3,6-dianhydro-D-maiuiitol (132), l,3 4,6-di-0-methylene-D-marmitol (13 134), and 1,3 4,6-di-O-benzylidene-D-mannitol (134). Examples of chiral crown compounds containing these residues include dd-92, dd-93, d-94, and d-95. Although not derived from carbohydrates—but rather (135) from the terpene, (-t-)-pulegone—... 

Chirality derived from the readily accessible a-amino acids has been incorporated into the side chains of aza and diaza macrocyclic polyethers. A number of procedures suitable for peptide synthesis have proved (178) to be unsuitable for acylating the relatively unreactive secondary amine groups of aza crown ethers. Eventually, it was discovered that mixed anhydrides of diphenylphos-phinic acid and alkoxycarbonyl-L-alanine derivatives do yield amides, which can be reduced to the corresponding amines, e.g., l-172. By contrast, the corresponding bisamides of diaza-15-crown-S derivatives could not be reduced and so an alternative approach, involving the use of chiral A-chloroacetamido alcohols derived from a-amino acids, has been employed (178) in the synthesis of chiral receptors, such as ll-173 to ll-175, based on this constitution. 

For incorporation of crown ethers and cryptates into the RTV encapsulant system as sodium and potassium ion scavengers, the total ionic contaminants must first precisely be determined. Atomic absorption is used to measure these ions in commercial silicone RTVs and silicone fluids. Values of "10 ppm for sodium and potassium were obtained in the best samples. Chloride level was determined by potentiometric titration of the silicone with AgN03. A quantity of ion trap (either crown ethers or cryptates) was then added to the RTV silicone encapsulant, and its molar concentration was equal to the combined sodium and potassium contaminant levels. 

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