Organic-Soluble 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... 

The main drawback of CMPO calixarenes is their low solubility in most of the diluents. Their concentration in the organic phase is not sufficient to allow lanthanides and actinides to be coextracted from HAW. Adamantyl groups improve the solubility of CMPO calixarenes. It would be interesting to continue to study these compounds and possibly to seek other ways to achieve a sufficient solubility (e.g., 0.1 M) of these calixarenes. 

The parent / -f-butylcalix[n] arenes (n = 4, 6, 8) are almost completely insoluble in water. However, their resemblance to crown ethers and spherands makes them interesting from the point of view of applications as phase transfer catalysts (Section 3.8.2). Table 3.20 shows the selectivity of calixarene 3.118 and its hexameric and octameric homologues for the extraction of various metal hydroxides into an organic receiving phase such as chloroform. Fortunately, in aqueous base the calixarenes are sufficiently soluble to act as phase transfer catalysts as a consequence of deprotonation of one of their phenolic hydroxyl groups. This solubility contrasts to [18] crown-6, which is much more effective in neutral solution. 

In aqueous solution, water-soluble calixarenes have the potential to bind much more strongly to organic guests than in lipophilic media because of the hydrophobic effect (Section 1.9). Unfortunately, p-alkylcalixarenes are not water-soluble and must be derivatised in order to take them up into aqueous... 

Among more complex macrocycles, Li et al. [47-52] reported the preparation and characterization of stationary phases incorporating calixarenes or calix-crowns bonded to silica. With individual columns, high selectivity was observed in the separation of alkylated aromatics, aromatic carboxylic acids, sulfonamides, nucleosides, and water-soluble vitamins. In other work, Sokoliess et al. [53] have characterized calixarene- and resorcinarene-bonded stationary phases similar to those described in the previous section of this chapter. And Huai et al. [54] used an end-capped p-tert-butyl-calix[4]arene-bonded silica phase for HPLC separation of a number of organic compounds. Resorcinarenes have also found application in GC. [55-57] Recently, exotic macrocycles have been used in capillary electrochromatography, as reported by Gong et al. [58]... 

In fact, traditional oxygen carrier molecules are dissolved in organic solvents. Only very few works focus on water-soluble carriers, such as Co-histidine which, however, suffers from very short lifetimes [28]. Therefore, a new type of water-soluble of Co-porphyrin with oxygen affinity was developed by Fiamrnengo et al. [43] for the PBM membrane. This novel carrier was based on the assembly of porphyrins with calixarenes. The self-assembly was driven by electrostatic interactions. The oxygen was assumed to complex inside the cavity of the porphyrin-calixarene assembly. Furthermore, the Co of the porphyrin was shielded from the other side by complexation with a nitrogenous base (1-methylimidazole or caffeine). 

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... 

Sugars, due to their chiral and polyhydroxylated nature, when coupled on either rim of a calixarene platform could constitute a unique class of water-soluble molecular receptors, which offer various opportunities for molecular recognition of chiral highly polar organic molecules in water and under physiological conditions. The synthesis of some such hybrids and their interactions are described. 

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. 

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."... 

Calixarenes, coined by C. D. Gutsche, are the cyclic oligomers produced by condensation of phenols and formaldehyde (1). In other words, they are cyclic phenol resins, but their physical and chemical properties are much different from those of linear phenol resins. Many of the calixarenes are crystalline and generally have poor solubilities in either water or in organic solvents. Their melting points are generally high, while ordinary phenol resins, novolaks, soften below 150°C. 

Here we consider some requirements on calixarenes as a nano-resist. The first to be considered is solubility, of course, to make films from solutions. Although Shinkai and his coworkers developed many water-soluble calixarenes, most of the calixarenes have poor solubilities either in water or in organic solvents and many of them are highly crystalline (1). An attempt to enhance solubility to organic solvents by substituting the upper rim with higher alkyl groups was in vain. 

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