Calixarenes ether derivatives

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]. 

As hosts for cations, the phenolic oxygen atoms at the calixarene lower rim (Figure 3.81) have the potential to act in a similar way to the anisole residues of the spherands, either in the original hydroxyl form or as alkyl ether derivatives. This kind of behaviour has been observed for the methyl ether of the parent /j-f-butylcalix[4] arene (compound 3.121) upon reaction with a mixture of sodium benzoate, one... 

Conformational fixing of calix[8]arenes is more difficult than in the case of the smaller calixarenes. Even bis-crown ether derivatives such as 1,3-5,7-calix[8]bis-... 

Only few investigations have been published on the gas-phase ion chemistry of host-guest complexes of calixarenes. With the advent of ESI mass spectrometry, especially when combined with ion-trap and FT-ICR mass spectrometry, this field has started to be developed. Binding selectivities of alkali metal ions to cahxarene-based crown ethers and open-chain ethers have been studied , the inclusion of neutral guests into the protonated resorcarene-based cavitand hosts by gas-phase ion-molecule reactions with amines have been studied and the formation of capsules from various calixarene tetraether derivatives and alkylammonium ions as ionic guests (notably enabling their detection by mass spectrometry) have been described recently . ... 

After the success ofVM-based ISEs, a number of synthetic ionophores were applied for the developments of respective ISEs. For alkali metal ions, crown-ether derivatives and calixarene derivatives were employed... 

Experimental work on new partitioning techniques is performed in the fiiamework of two projects. The first one has the objective to develop processes for the separation of minor actinides from very acidic aqueous solutions containing high level waste without the generation of secondary solid waste. In the second one, extractants selective to strontium, actinides -I- lanthanides, and actinides only such as calixarene and crown ether derivatives will be synthesised. The extracting properties of these compounds will be determined experimentally and modelled with molecular mechanics and molecular dynamics simulations. 

The functionalization of the phenolic OH groups of calixarenes at the lower rim has been performed both for shaping the macrocycle through conformational control (especially for calix[4]- and calix[5]arenes) or for attaching recognition moieties for performing supramolec-ular functions. Obviously, direct acylation or alkylation (Williamson method), to achieve ester and ether derivatives, respectively, are the most extensively used functionalization... 

Calixarenes, resorcinarenes, and their simple ether derivatives have an electron-rich, 7r-basic cavity, which is able to host cations and neutral molecules but not anions, which, therefore, do not form en Jo-cavity inclusion complexes with these receptors. However, direct TT-metallation of the exterior of the macrocycles provides a vacant cavity with altered electrostatic properties. Indeed, the ability of certain transition metal ions... 

Many other cyclic and noncyclic organic carriers with remarkable ion selectivities have been used successfiilly as active hosts of various liquid membrane electrodes. These include the 14-crown-4-ether for lithium (30) 16-crown-5 derivatives for sodium bis-benzo-18-crown-6 ether for cesium the ionophore ETH 1001 [(R,R)-AA -bisd l-ethoxycarbonyl)undecyl-A,yVl-4,5-tctramcthyl-3,6-dioxaoctancdiamide] for calcium the natural macrocyclics nonactin and monensin for ammonia and sodium (31), respectively the ionophore ETH 1117 for magnesium calixarene derivatives for sodium (32) and macrocyclic thioethers for mercury and silver (33). 

Polymer supported xanthene derivatives have been used in the solid phase synthesis of 1-aminophosphinic acids, RCH(NH2)PH(0)0H, <%TL1647> and of C-terminal peptide amides <96JOC6326>. Xanthene units also feature in crown ethers <96JCS(P2)2091>, calixarenes <96JOC5670> and in a flexible template for a P-sheet nucleator <96JOC7408>. 

With the alkynyl functionality greater than two, starbust type complexes are obtained, as derived, for example, from 1,3,5-trialkynylbenzenes 85 or -triazines,86 1,1,2,2-tetraalkynylethenes,85 or bis(l,2-dialkynyl)phenylene-bridged crown ethers or calixarenes. ... 

The hemispherands, spherands, calixarenes, and related derivatives. A number of hosts for which the pre-organization criterion is half met (the hemispherands) (Cram et al., 1982) or fully met (the spherands) (Cram, Kaneda, Helgeson Lein, 1979) have been synthesized. An example of each of these is given by (251) and (252), respectively. In (251), the three methoxyl groups are conformationally constrained whereas the remaining ether donors are not fixed but can either point in or out of the ring. This system binds well to alkali metal ions such as sodium and potassium as well as to alkylammonium ions. The crystal structure of the 1 1 adduct with the f-butyl ammonium cation indicates that two linear +N-H - 0... 

Supramolecnlar derivatives containing crown ether [228], calixarenes [264, 265] or dendrimers [267, 279] have been synthesized with the precursors shown in Table 4.10. Fullerene-flavonoid [268] or the fuUerene glycoconjugate [258] derived from 237 and 235, respectively, are expected to show biological activity. 

Calixarene derivatives involving crown ethers like 233 exhibit complexation ofalkali or ammonium cations typical of crown ethers that is especially effective in the partial cone conformation [26]. By a proper functionalization selective synthetic receptors for specific hosts have been developed. For instance, two 2,4-diaminotriazine groups at diametrical positions of the upper rim of a... 

Calixarene crown-6 compounds, which are neutral extractants like crown ethers, are able to coextract technetium with cesium. Tests carried out with several calix-arene-crown ethers (MC7, MC8, MC14, BC2, BC5, BC8, and BC10) show that the extraction of technetium, present in the aqueous phase at a concentration 10 5 M, is enhanced as the cesium concentration in the aqueous phase increases from 10 5 to 10-2 M. As expected, an increase of nitrate concentration prevents pertechnetate extraction in competition with nitrate anion. The extraction of technetium is only appreciable when the nitric acid does not exceed 1 M. Distribution ratios DCs (close to 8) are comparable for the various calixarenes. However, a decrease of extraction is observed for naphtho derivatives.88 89... 

Several classes of synthesized calixarenes bearing several moieties (ether, ester, and amide derivatives), were tested for the extraction of strontium picrates (from aqueous solutions into dichloromethane).128 Only a few of them show appreciable extraction levels. The p-i-butyl calix[6]arene hexa(di-/V-ethyl)amide (CA4) shows a very high extraction level of alkaline earth cations with respect to alkali metal cations. Moreover, dealkylation of the calix[6]arene hcxa(di-/V-cthyl)amidc (CA5) decreases the extraction of both sodium and strontium. As this decrease is much more important for sodium than for strontium, the Sr/Na selectivity, which increases from 3.12 to 9.4, is better than that achieved for DC18 derivative under the same conditions (8.7). These results were confirmed by extraction of strontium (5 x 10 4 M) from 1 M HN03 solutions, where it was found that p-t-butyl calix[4]arene tetra(di-N-ethyl) amide (CA2) (10 2 M in NPOE) extracts only sodium (DNa = 12.3, DSl < 0.001). 

The relatively low thermodynamic stability of complexes of hemicarcerands or other container-type hosts is a direct consequence of structural aspects of the walls that make up the inner surface of such compounds. These walls are lined by aromatic subunits while free electron pairs of heteroatoms such as those of the ether oxygen atoms are preferentially oriented to the outside. Complexes are therefore enthalpically stabilized only by weak dispersive interactions. In the case of positively charged guests cation-re interactions can contribute to binding enthalpy as in a self-assembled calixarene-derived capsule [9], but directed interactions such as hydrogen-bonding interactions are usually absent. 

Probably the first examples of chiral calixarene derivatives were esters with camphorsulfonic acid24 derived from t-butyl-calixfSjarene.25 Later ethers obtained with (S)-2-methylbutyl bromide were synthesized and studied with respect to their CD spectra and their chiral recognition ability.26... 

The etherification of calixarene analogues containing methylene and 1,3-propylene bridges leads in good yield and regioselectively to 1,3-di-O-substituted derivatives 90.175 To prevent enantiomerization the ether residues must be at least propyl... 

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