Bis -18-crown-6-ether

Not long thereafter, Tarnowski and Cram reported the first example of a hinged bis-crown ether. The compound was prepared in the usual Williamson reaction by heating a mixture of 2,2, 3,3 -tetrahydroxy-l, r-binaphthyl with pentaethylene glycol ditosylate and KOH in aqueous THF solution. The product (mp 159.5—161°) shown in Eq. (3.30) was obtained in 30% yield. This compound was shown to complex bis-ammonium cations of several varieties . 

Sol-gel-derived membranes encapsulating a bis(crown ether) derivative [bis(12-crown-4-ylmethyl) 2-dodecyl-2-methylmalonate] [28] were also fabricated with an initial DEDMS/TEOS ratio of 3 for Na -ISFETs. The Na -ISFETs showed a Nernstian response to Na+ activity changes in the activity range of 1 x 10 " to 1 M and a short response time of 2 s. Employment of a polythiophene interlayer improved the potential instability and the lower detection limit in both of the K - and Na -ISFETs based on the sol-gel-derived membranes with the initial DEDMS/TEOS ratio of 3 (Fig. 8). 

E. Lindner, K. Toth, M. Horvath, E. Pungor, B. Agai, I. Bitter, L. Toke, and Z. Hell, Bis-crown ether derivatives as ionophores for potassium selective electrodes. Fres. Z. Anal. Chem. 322, 157-163 (1985). 

Additional macrocyclic polyether groups show no co-operative effect when the polyether rings diverge. For instance, the bis(crown ethers) [58] and [59]... 

Studies on the Schiff base linked ferrocene bis-crown ether compound [6] have shown that it is not well-behaved electrochemically. 

FABMS has been used as a semiquantitative indication of the selectivity of receptors for particular guest metal cations (Johnstone and Rose, 1983). The FABMS competition experiment on [7] with equimolar amounts of the nitrates of sodium, potassium, rubidium and caesium gave gas-phase complex ions of ([7] + K)+ ion (m/z 809) and a minor peak ([7] + Rb)+ ion (m/z 855) exclusively. The relative peak intensities therefore suggested a selectivity order of K+ Rb+ Na+, Cs+, indicative of the bis-crown effect, the ability of bis-crown ether ligands to complex a metal cation of size larger than the cavity of a single crown ether unit, forming a sandwich structure. 

We have recently demonstrated (Beer et al., 1995b,c) that it is possible electrochemically to detect simultaneously the presence of two different cations bound in the redox-active ferrocene bis-crown ether receptor [15] as shown in Fig. 10. 

We synthesized bis crown-ethers 1 and 2 in which cations can be well accomodated between the two ligand units, thus giving rise to sandwich complexes ( ) which can be expected to have complexation constants higher than those of crown-ethers. 

Bis(crown) ethers [208] have been used for the T1(I) ISE. Where glass microelectrodes cannot be used for pH determination because of their fragility, microelectrodes with ligand XXXI can be used for [118],... 

Bis[copper(U) tris-pyrazolyl borane] dioxygen complex, 42 107-108, 110 Bis crown ethers, see Ferrocene, crown and bis crown ethers... 

Coordinated transition metal redox-active macrocycles, 39 108-124 ammonium cation, 39 128-133 crown ether and bis crown ether ligands containing bipyridyl transition metal recognition sites, 39 111 crown ether dithiocarbamate and dithiolene complexes, 39 123-124 metalloporphyrin crown ether compounds, 39 108-109... 

Sophisticated lonophores Long Glyme, Lariat Ether, Bis(crown ethers), and lonophore Antibiotic °... 

We now proceed to more complicated ionophores in order to testify the validity of this extrathermodynamic relationship and its hypothetical interpretation as an attempt to understand the nature of supramolecular interactions more generally and deeply. The thermodynamic parameters are plotted in Figures 16-19 for long glymes, (pseudo)cyclic ionophore antibiotics, lariat ethers with donating side-arm(s), and bis(crown ethers), whose structural changes upon complexation are schematically illustrated in Figure 20. 

For this puq)ose, the photoswitchable bis(crown ether)s 88 and 89 as well as the reference compound 90 have been synthesized. Compounds 88 and 89 are highly lipophilic derivatives of azobis(benzo-15-crown-5). The parent azobis crown ether was originally developed by Shinkai and its photoresponsive changes in complexation, extraction, and transport properties thoroughly examined. Compared to 87, more distinct structural difference between the cis and trans isomers can be expected for 88 and 89 because in the latter compounds the 15-crown-5 rings are directly attached to the azobenzene group. The photoequilibrium concentrations of the cis and trans forms and the photoinduced changes in the complexation constants for alkali metal ions are summarized in Table 7. 

Thuery, P., Nierlich, M., Bryan, J.C. et al. 1997. Crown ether conformations in 1,3-calix[4]arene bis(crown ether) Crystal structures of a cesium complex and solvent adducts and molecular dynamics simulations. J. Chem. Soc. Dalton Trans. 1997 (22) 4191 4202. 

It has been established that alkali metal cations exactly fitting the size of the crown ether ring form a 1 1 complex whereas those that have larger cation radii form a 1 2 sandwich complex. This view was clearly substantiated by using bis(crown ethers). For instance, Kimura et al. [10] reported that the maleate diester of monobenzo-15-crown-5 ((Z)-form) extracts K+ from the aqueous phase... 

Fedorov, Yu., Fedorova, O., Schepel, N., Gromov, S., Alfimov, M., J. Saltiel (2004) Synthesis and multitopic complex formation of die photochromic bis-crown ether based on benzobis(thiazole), J. Phys. Org. Chem., in press. 

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