Crown-ether head groups

Closely related to the crown ether adducts are the two intramolecular arenediazonium ion-crown ether compounds 11.6 and 11.7 which were synthesized by Gokel s group (Beadle et al., 1984b). Infrared and lH NMR spectra are consistent with the insertion of the diazonio group into the 21-crown-7 cavity. The complex 11.6 can therefore be described not in an anthropomorphic, but in a zoomorphic way, as an ostrich complex reflecting the common belief that an ostrich hides its head in a hole when endangered. For the complex 11.7 the spectra correspond to... 

This idea was realized using crown ether styryl dyes (CESD) lc,d, 4c (Scheme 1,4). The compounds lc,d, 4c having betaine structures form supramolecular dimers with a crossed arrangement of molecules (a h-head-to-tail) in the presence of ions, due to the intermolecular interaction between the sulfo group of one of the molecules and a ion located in the crown-ether cavity of the other molecule [20,21], It was shown that photoirradiation of solutions of dimer results in stereospecific PCA giving only one of the 11 possible derivatives of cyclobutane, which is expected in conformity with the concerted superficial (s,s) addition of the reactants (Scheme 5) [22,23], It is noteworthy... 

Subsequently, the ion channel activity of 34 was studied using planar bilayer methods.50c Peptide 34 was either introduced to the bulk KC1 solution or mixed with the lipid sample prior to bilayer formation. In the first method, incorporation proved difficult, possibly due to the high tendency of 34 to form aggregates. In the second method the stability of the bilayer was perturbed and single-channels were not obtained. It was postulated that this was due to the adsorption of the peptide onto the surface of the membrane due to electrostatic interactions of the crown ethers with the polar head groups. However as soon as the peptide was incorporated successfully into the bilayer, i.e. peptide parallel to the lipid hydrocarbons, singlechannel events were recorded indicative of 34 functioning in a unimolecular fashion. 

In addition to crown-ethers, calix[4]resorcinarenes 19 have also been used as head groups to obtain azobenzene amphipbiles with sufficient photo-isomerization in LBK films. For this purpose, azobenzene moieties have been tethered to the lower rim of the crown conformer of the calixarene. O-octacarboxymethoxylated calix[4]resorcinarenes 19 (X = CH2-COOH) display efficient trans to cis photoisomerizability in densely packed mono-layers on a water surface, in LBK films, and in surface-adsorbed monolayers, whereas the noncarboxymetylated 19 (X = H) derivative gives films that are too densely packed. However, the aggregation is already suppressed efficiently compared to the azobenzene derivative without calixaren. ... 

Macrocyclic compounds with a paraffinic chain have first been described by Cinquini et al.107). In aqueous solution they form readily micelles with CMC values ranging between 10-5 and 10-3 M depending on the exact nature of the head group and the chain length168,169). Crown ether surfactants are particularly suited to serve as electron relays in redox events since different metal ions covering a wide range of standard potentials may be inserted into the macrocyclic ring. Consider, for example, the crown 5-n-tetradecyl-... 

The internal cavity of a cyclophane is endobasic if functional groups are present that are basic or electron donating the most obvious groups include the ethers, pyridines, amines, and phosphorus-based donors. Cyclophanes in this category would be expected to bind metal ions and also promote H-bonding interactions within the cavity. Hence, in this section, crown ethers and azamacrocycles could easily be included. Under this heading, we can also... 

We felt confident that the crown compounds would be amphiphilic. Indeed, a metal-cation-bound crown head group should certainly approximate a diffuse positive charge. At the time this work was undertaken, however, there was no evidence that either a crown or its complex could form such organized assemblies as vesicles. We were able to obtain direct evidence for the formation of vesicles from the steroidal lariat ether illustrated. llie essential characteristics of the vesicles produced is that they are unilamellar, their size is in the range 340-350 A, and the volume entrapments were about 4%. Much of this work has been summarized in a recent review article. ... 

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