Organic cation complexation. calixarenes

The performance of calixarenes as cation carriers through H20-organic solvent H20 liquid membranes has also been studied.137 In basic metal hydroxide solutions, the monodeprotonated phenolate anions complex and transport the cations, while [18]crown-6 does not, under the same conditions. Low water solubility, neutral complex formation and potential coupling of cation transport to reverse proton flux have been cited as desirable transport features inherent in these molecules.137... 

Calixarenes without ionisable substituents at the wider rim are not water soluble. Their complexation behaviour towards organic cations, has, therefore, been studied mainly in lipophilic solvents such as CDCI3 and (CDCl2)2- The cation- r interaction is the main contribution to the stability of complexes and the association constants are rather low, ranging from 10 to lOOOM (see Table 12.1). 

Studies of water soluble calixarenes such as II-IO (Scheme 12.8) in complex with organic cations in aqueous media have been most useful because this system represents a typical... 

The impact of different surfactants (SDS, DOSS, CTAB and hexadimethrine bromide, bile salts °), nonionic and mixed micelles, and additives (neutral and anionic CDs," " tetraalkylammonium salts, organic solvents in EKC separations has been demonstrated with phenol test mixtures. In addition, phenols have been chosen to introduce the applicability of more exotic EKC secondary phases such as SDS modified by bovine serum albumin, water-soluble calixarene, " starburstdendrimers, " " cationic replaceable polymeric phases, ionenes, amphiphilic block copolymers,polyelectrolye complexes,and liposome-coated capillaries. The separation of phenols of environmental interest as well as the sources and transformations of chlorophenols in the natural environment have been revised. Examples of the investigation of phenols by EKC methodologies in aquatic systems, soil," " and gas phase are compiled in Table 31.3. Figure 31.3 illustrates the electromigration separation of phenols by both CZE and EKC modes. 

Regarding the threading with dialkylammonium ions, simple ethers of calixarenes can be seen as modified crown ethers and in principle they should be able to give cn io-complexation of such organic cations in a similar way [6], Unfortunately, with the notable exception of some calix[5]arene derivatives [16], simple ethers of calix[n]arenes do not complex halide, hexafluorophosphate or tetraphe-nylborate salts of dialkylammonium cations. 

Later Shinkai and coll, have reported several upper rim sulfonated calixarenes (e.g. 24), which have a much higher water solubility than 23 and are able to complex organic cations and neutral molecules in water solution [28]. Therefore, we synthesized a tetracarboxylic acid tetrasulfonate 25 in the fixed cone structure in order to compare its binding properties with those of the flexible tetrasulfonate 24, also studied by Atwood and coll. [33]. 

Since 1991 we have developed the synthesis of macropolycycles containing in their molecular structure the monocyclic structure of calixarenes and crown ether elements. This combination gives a close coupling of the hydrophobic cavity of the calixarenes able to include organic substrates and the metal cation complexing sites of the crown ether, with potential interactions between them. We have already demonstrated evidence of such cation-substrate contact during a triple inclusion by a calixarene [10]. The crystal structure of the Eu(III) complex of his-(homooxa)-p-rerr-butylcalix[4]arene showed the Eu(in) to be coordinated to a DMSO molecule included in the hydrophobic cavity of the calixarene [10]. 

Cage complexes of homo- and heterodimeric hydrogen-bonded capsules 414-416, the derivatives of calixarene tetraurea-containing ligand syntones and their analogs, with encapsulated organic cations shown in Scheme 3.77, have been detected in gas phase using ESI-MS method [76]. The competition experiments with different... 

Since in the case of p-H calixarenes, a precipitate occurred at the water/organic interphase, extraction tests were carried at a concentration of 10" M for these compounds. The presence of tert-butyl or benzyloxy at the wide rim helps to solubilize the complexes. The distribution ratios are compared to wide-rim CPw3 and narrow-rim CPn3 (Table 4.34).179 For all CMPO-calix[6,8]arenes, distribution ratios of the two cations studied (Eu and Am) increase with increasing HN03 concentration, in agreement with what is observed with tetramers bearing CMPO residues... 

The sulfonate derivatives (Fig. 4A), in which introduction of suitable ligand functions takes place at the para-position of the aromatic ring, are the most widely studied of the w ater-soluble calixarenes. Their solid-state binding to a wide range of metallic cations and complexes was reviewed by Raston and Atwood. The ability of these molecules to intercalate cations in expandable layers between bilayers of para-sulfonato-calix[4]arene led Atwood and Coleman in 1988 to name these systems Organic Clays." (Fig. 4C). Since then. Atwood extended the structural types observed to include liposomal analogues, tubes, and various Archimedian and Platonic solids."... 

The chemical behavior of clays is also mimicked by the title complexes in two respects the presence of cation-exhange capabilities and the reduced water content in the ammonium salt [20]. Currently, other similarities between clays and the water-soluble calixarenes are being probed. In particular, the size- and polarity-selective cavity of the calix[4]arene sulfonates is finding utility in the separation of organic substances, cations, anions, and neutral molecules, from aqueous feed streams. 

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