Crown liquid-like

Beckham and coworkers studied the dynamic mechanical properties of poly(urethane-crown ether rotaxane)s [138]. No difference was observed between the backbone and polyrotaxane, probably because of the low min value (0.02). However, 13C solid-state NMR detected die presence of the crown ether as a mobile structure at room temperature. The same observation was seen in polyrotaxanes with ether sulfone and ether ketone backbones (77-80) [114]. Although no detailed properties were reported, the detection of the liquid-like crown ether provided very important information in terms of mechanical properties, because these properties are the result of molecular response to external forces. For example, mobile crown ethers can play the role of plasticizers and thus improve impact strength. 

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. 

Channel-like architectures are formed in the mesophase given by complexes of long chain crown ether derivatives [8.196a,b] and long-chain calixarene derivatives display columnar liquid-crystalline arrangements [8.196c]. Self-assembled tubular structures based on cyclic peptide components have been described [8.186]. 

Bayle presented liquid crystal 34 (Scheme 19) bearing four aromatic units linked by ester and azo functional groups [56]. Two butyloxy groups are attached at the ends of the molecule and the crown ether is bound at the side of the molecule. The nematic phase exhibited by 34 is quite broad (AT = 96 K). Upon complexation with LiBF4, the nematic range diminishes with increasing amounts of added salt and disappears completely at 0.5 equiv. of added LiBF4 which is most likely due to the formation of a 2 1 crown lithium complex. From 0.2 equiv. of salt, a smectic... 

Percec studied taper-shaped molecules like 67 and 68 (Scheme 35) and investigated their liquid crystalline properties upon complexation with NaOTf and KOTf [84, 85]. It was found that the neat materials exhibit only crystalline phases with 67 melting at 60 °C and 68 melting at 94 °C. The increased melting point in the latter system can be explained by the presence of an additional aromatic ring. Both 67 and 68 consist of an endo-receptor (the [15]crown-5 macrocycle) and an exo-receptor (the taper-shaped 3,4,5-tris(p-dodecyloxybenzoate)). 

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... 

Crown ethers discussed in this section possess rod-like substituents all around them or flat substituents at either end (Fig. 14). The former was the structure of the first liquid crystalline crown-like molecules and will be discussed first. The latter one comprises molecules with taper- or disk-shaped terminal groups. 

The operational performance of an HF-based ESTM technique was first described by Liu et al.71 A 15-cm piece of HF was filled with an acceptor buffer solution, after which the F1F was made into a loop. This loop-like F1F device was soaked in n-undecane, and then immersed in 1 L of a river or leachate water sample for extraction of freely dissolved chlorophenols. This FIF-loop device was also employed for selective ESTM sampling of freely available Cu+2 in leachate water.78 The selectivity stemmed from a selective liquid membrane (di-n-dihexyl ether) containing a carrier (crown ether/oleic acid) and a selective stripping agent in the acceptor solution. 

The synergistic effect was only found in mixed stationary phases that have a special selectivity. Those stationary phases were CD, crown ether, liquid crystal-hne, resorcarene, calixarene, AgNOs, and others. Crown ether, CD, cahxarene, and resorcarene possess cyclic moieties with cavity-like structures that are able to form inclusion complexes with metal ions and organic molecules. Liquid crystalhne stationary phases have temperature-dependent ordered structures and the retention is governed by the solute s length-to-breadth ratio. AgNOs retards olefins by the formation of loose adducts. Together with the above special selectivity stationary phases, they have already been the focal point of sup-ramolecular chemistry. 

The polarity of some l-alkyl-3-methylimidazolium ionic liquids has been probed using the solvatochomic dye Nile Red (Figure 1(d)), and found to be comparable to that of lower alcohols.31 As such, polar organic solvents like dichloromethane and diethylether are miscible with ionic liquids, solvents of low polarity show partial miscibility, and nonpolar solvents are essentially immiscible. Extractants such as crown ethers can be used to extract cations such as Na+, Cs+, and Sr2+ from ionic liquids.32... 

From measurements of the dielectric constant of liquid sulfur in the temperature range 134-206 °C [15] it was concluded that the molar polarization increases from 134-159 °C which was explained by the assumption of a temperature dependent equilibrium between Ss(crown) and Ss(chair) molecules, the latter possessing a permanent dipole moment owing to their low symmetry (Cs). However, the most natural rationalization of the findings is that certain components of r-sulfur like Sy and Sg—molecules of low symmetry possessing a dipole moment—contribute to the molar polarization. Since their concentration increases with temperature up to the polymerization transition it is to be expected that the molar polarization changes accordingly. Above 159 °C the molar polarization is proportional to the polymer content of the melt. 

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