Crown ether moieties

By considering the stability constant and the lipophilicity of host molecules, Fyles et al. synthesized a series of carboxylic ionophores having a crown ether moiety and energetically developed the active transport of alkali metal cations 27-32). Ionophores 19-21 possess appropriate stability constants for K+ and show effective K+-selective transports (Fig. 5). Although all of the corresponding [15]crown-5 derivatives (22-24) selectively transport Na+, their transport rates are rather slow compared with... 

Figure 7.5.2. C60 derivative monolayer self-assembled as a result of ammonium cation recognition by crown ether moiety.

The basket compounds contain two crown ether moieties, which are good binders of alkali metal ions. It was therefore expected that these compounds... 

The presence of two crown ether moieties in the baskets allows the simultaneous binding of two ammonium groups. Organic diammonium salts of type H3N(CH2)nNH3 are bound very strongly, as is evident from the high association constants in Table 5 [19]. 

Yam, V.W.-W. and Lu, X.-X.C.-C. (2003) First observation of alkali metal ion induced trans-cis isomerization of palladium(ll) phosphane complexes containing crown ether moieties. Angeiv. Chem., 115, 3507-3510. 

Usually, the crown ether moiety is introduced into the peptide sequence by using a side-chain-modified amino acid. Either a nonchiral crown ether is attached to the side chain of lysine1151 or glutamic acid1101 or the crown is built on the catechol side chain of dihydroxy-L-... 

A new functionalized polysiloxane bearing crown ether moieties in the main chain as well as its platinum complex are prepared from 3,19-dihydroxy-l-thia-5,8,ll,14,17-pentaoxacycloicosane through ether formation with ro-chloroundecene, followed by hydrosilylation with triethoxysilane, copolymerization with octamethylcyclotetrasiloxane and reaction with potassium chloroplatinate279. 

Another mechanism to obtain polymers is cationic polymerization. Monomeric 24 which already displays a broad nematic phase could be polymerized to poly(24) (Scheme 13) which displays an even broader phase [37]. Neither the triple bond nor the crown ether moiety in 24 was affected by the harsh conditions for polymerization (EtAlCl2, SMe2). 

Percec and Rodenhouse presented the first main-chain liquid crystalline polymer with a crown ether moiety in the backbone of the polymer [83], Liquid crystalline polyethers 63 were obtained by phase transfer catalyzed polyetherification of... 

Upon addition of NaOTf, columnar hexagonal mesophases could be induced. For 68, 0.4 equiv. of salt were needed while for 67, only 0.2 equiv. of NaOTf were needed for mesophase induction. Upon complexation, the complexed crown ether moieties and the anions self-assemble within a supramolecular tube and the taper-shaped side groups stack over each other in the periphery. X-Ray scattering... 

Gitsov presented a series of poly(benzyl ether) monodendrimers capable of cation complexation lacking alkyloxy side chains which were non-mesomorphic [93], Laschat followed a different route to obtain disk-like liquid crystals equipped with crown ether moieties. The crown ether was not attached to the mesogenic... 

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