Crown ether macrocycles

Many chiral compounds can be used as selectors, for example, chiral metal complexes, native and modified cyclodextrins, crown ethers, macrocyclic antibiotics, noncyclic oligosaccharides, and polysaccharides all have been shown to be useful for efficient separation of different types of compounds. 

The sensor covalently joined a bithiophene unit with a crown ether macrocycle as the monomeric unit for polymerization (Scheme 1). The spatial distribution of oxygen coordination sites around a metal ion causes planarization of the backbone in the bithiophene, eliciting a red-shift upon metal coordination. They expanded upon this bithiophene structure by replacing the crown ether macrocycle with a calixarene-based ion receptor, and worked with both a monomeric model and a polymeric version to compare ion-binding specificity and behavior [13]. The monomer exhibited less specificity for Na+ than the polymer. However, with the gradual addition of Na+, the monomer underwent a steady blue shift in fluorescence emission whereas the polymer appeared to reach a critical concentration where the spectra rapidly transitioned to a shorter wavelength. Scheme 2 illustrates the proposed explanation for blue shift with increasing ion concentration. 

In summary, it can be stated that for screening approaches in CE, only CD derivatives have been used. Other chiral selectors occasionally applied in CE, such as crown ethers, macrocyclic antibiotics, and chiral surfactants [39], were not found to be involved in (generic) screening approaches for chiral separations. 

A molecule that contains one or more binding sites that can accommodate inorganic or organic ions referred to as guests. The binding site could even be a cavity within a crystal structure. Although enzymes clearly qualify as examples of host molecules, the term is usually restricted to structures such as crown ethers, macrocycles, and cyclodextrins. Nevertheless, these hosts do serve as models for molecular recognition. See also Crown Ethers Macrocycles Inclusion Complexes... 

HORN-BORNIG PLOT HORSERADISH PEROXIDASE HOST-GUEST INTERACTIONS HOST MOLECULE CROWN ETHERS MACROCYCLES INCLUSION COMPLEXES HOCKEL MOLECULAR-ORBITAL CALCULATIONS... 

The introduction of aryl groups to the ring tends to stiffen the macrocycle and decrease the donor ability of the oxygens in crown ether macrocycles.1,21... 

Jankowski, C.K., Dozol, J.F., Attain, F. et at. 2002. Nitration of calixcrown 6 influence on extracting abilities. Use of cesium salts for detection of crown ether macrocycles with the electrospray ionization mass spectrometry technique. Polish J. Chem. 76 701-709. 

Figure 3.28 Stabilities of podand (acyclic), crown ether (macrocyclic) and cryptand (macrobicyclic) complexes of K+.

The triazolines (97), were synthesized from the triazolinethione (95) by oxidation to the sulfonic acid and subsequent treatment with H20 and HC1 at 20-100° [95EUP657437], The 1,2,4-triazole intermediate (98), prepared from the N-unsubstituted triazole by reaction with 4-MeOC6H4CH,Cl and KjCO, with tetrabutylammionium hydrosulfate for 3 h at 60°, was further elaborated to chiral crown ether macrocycles [94S1091]. 

Electrochemical Group IA Metal Cation Dependence of Quinone and Nitroaromatic Crown Ether Macrocycles... 

Complexation of metal ions by Pcs adsorbed on metal surfaces has also been reported. In fact, a CoPc adsorbed on Au(lll) is able to complex two Ca(II) ions by two of its four peripherally substituted crown ether macrocycles as demonstrated by high-resolution STM studies [196], Furthermore, it was demonstrated by using a Au(100)-(1 x 1) lattice surface that the relationship between the crown ether moieties of the CoPc and the underlying Au lattice is important in the trapping of the Ca(II) ions within the crown macrocycles [197],... 

Fig. 27 Examples of thermodynamically controlled reactions employed in the near-quantitative synthesis of MIMs. (a) Disulfide-exchange reaction permits equilibration between a bis(ammo-nium) disulfide dumbbell and a crown ether macrocycle to yield a mixture of [2]- and [3]rotaxanes quantitatively [194], (b) Olefin metathesis at high concentration on a benzylic amide macrocycle greatly favors the catenated species [196]. (c) Self-correcting imine bonds allow for nearly quantitative selection of a [2]rotaxane from an appropriate dynamic combinatorial library [76], (d) A weak nucleophile (E) equilibrates the components of a donor-acceptor [2]catenane in a dynamic Sn2 reaction [205]...

Fig. 30 Polymeric blue box cyclophane displays the emergent property of quantitative thermodynamic catenation by iodide-catalyzed self-assembly with an appropriate crown ether macrocycle. The analogous monomeric and dimeric species do not react quantitatively [207]...

In manganese(II) compounds incorporating crown ether macrocycles, the metal is generally H-bonded to the crown via water molecules, although it has been possible to isolate some compounds such as [Mn(12-crown-4)2]+ and [Mn(15-crown-5)(CF3803)2], in which all the ether oxygen atoms of the crown bind directly to manganese(II). ... 

Most carbohydrates contain ethane-1,2-diol fragments, therefore they were also successfully included into crown ether macrocycles [313]. Polyvalency of carbohydrates was studied based on dendrimeric structures which were generated on successful glycosylations of highly branched polyethylene glycol units [314]. 

Due to their pronounced selectivity in metal ion ccmplexation (6), crown ethers (macrocyclic polyethers) and related macrocyclic multidentate ligands are attractive mobile carriers for metal ion transport across liquid membranes. As summarized in recent reviews of macrocycle-facil itated transport of ions in liquid membrane systems (7,8), most studies have been conducted with macrocyclic carriers which do not possess ionizable groups. For such carriers, metal ions can only be transported down their concentration gradients unless some type of auxiliary complexing agent is present in the receiving aqueous phase. 

Finally, x-ray determinations at small angles of (72) and [Cu-(72)], by Simon and co-workers showed that the phthalocyanine moieties are superposed in an eclipsed conformation and that the crown ether macrocycles form channels <87CPL(139)362>. 

Beer. P.D. Crowe. D.B. Ogden, M.I. Drew, M.G.B. Main. B. Ammonium redox-responsive receptors containing multiple ferrocene and quinone redox-active centers attached to di-aza and tri-aza crown-ether macrocycles. J. Chern. Soc., Dalton Trans. 1993. 2107-2116. 

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