Calixarenes water soluble

In principle, there are four basic strategies to compensate for the repulsive effects between the hydrophobic fullerene surface and water (a) encapsulation in the internal hydrophobic moiety of water-soluble hosts like cyclodextrins (Andersson et al., 1992 Murthy and Geckeler, 2001), calixarenes (Kunsagi-Mate et al., 2004) or cyclotriveratrylenes (Rio and Nierengarten, 2002) (b) supramolecular or covalent incorporation of fullerenes or derivatives into water-soluble polymers (Giacalone and Martin, 2006) or biomolecules like proteins (Pellarini et al., 2001 Yang et al., 2007) (c) suspension with the aid of appropriate surfactants and (d) direct exohe-dral functionalization in order to introduce hydrophilic moieties. 

Kunsagi-Mate S, Szabo K, Bitter I, Nagy G, Kollar L (2004) Complex formation between water-soluble sulfonated calixarenes and C60 fullerene. Tetrahedron Lett. 45 1387-1390. 

Low affinity to polar solvents and fullerenes aggregation in water limit their use in biologic systems. To increase water solubility of fullerenes, few ways are used solubilization with the use of some water-soluble polymers like PDT or polyvin-ilpyrrolidone, generation of complexes with cyclodextrines or calixarenes, and... 

Water-soluble calixarenes are more and more investigated in order to make use of their ability to host other molecules, and the first examples of the use of phosphine-modified calixarenes in organometallic catalysis appeared just recently. Rhodium complexes prepared with 197 (Figure 19)... 

Similarly, a series of hydroxy-terminated poly(ether) dendrimers, 35, with a single carborane nucleus at their core, were observed to have water solubilities comparable to that of chloroacetic acid, or D,L-valine. Again this is in direct contrast to the starting carborane nucleus which is insoluble in aqueous solutions and permitted the use of 35 in neutron capture therapy. Similar effects have also been observed with dendrimers containing calixarenes [66] and porphyrins [67] as the central units. 

It had been reported that fullerene Cgo forms a water-soluble complex with y-cyclodextrin by heating with an excess amount of y-cyclodextrin in water [10] or in a mixture of refluxing water and toluene for a long time, such as 30 h [ 11]. The isolated complex is considered to have the Cgo structure bicapped with y-cyclodextrin in a molar ratio of 1 2 [11], and the complex dissolved in water to give a solution of C o with a concentration of nearly 10 mol L 410,11 ]. Fullerene Qo was also solubilized in water by complexation with a sulfocalix[8] arene, i.e., calix-[8]aryloxy-49,50,51,52,53,54,55,56-octakis(propane-3-sulfonate). The concentration of this complex in water is estimated as 5x10 mol L [12]. Complex formation between fullerene and various calixarenes has also been reported [8]. 

Alkenes and Alkynes. A series of metal carbonyl cations, such as [Au(CO)n]+,287,288 [c-Pd( i-CO)2]2+,289 [Rh(CO)4]+,290 and [(Pt(CO)3)2]2+,291 was found to induce the formation of carboxylic acids from alkenes and CO in the presence of H2SO4 under mild conditions. A novel water-soluble Pd catalyst292 and Pd complexes of calixarene-based phosphine ligands293 showed high activity in the regioselective carboxylation of vinyl arenes to yield 2-arylpropionic acids or... 

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... 

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... 

Arena, G., Casnati, A., Contino, A., Lombardo, G. G., Sciotto, D., and Ungaro, R. (1999) Water-soluble calixarene hosts that specifically recognize the trimethylammonium group or the benzene ring of aromatic... 

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]... 

Karakhanov E, Buchneva T, Maximov A et al (2002) Substrate selectivity in byphasic Wacker-oxidation of alkenes in the presence of water-soluble calixarenes. J Mol Catal A Chem 184(1-2) 11-17... 

Diamba HM et al (2009) Towards calixarene-based prodrugs drug release and antibacterial behaviour of a water-soluble nalidixic acid/calix[4]arene ester adduct. Bioorg Med Chem Lett 19 2679-2682... 

The introduction of -S03H groups at the upper rim of calixarenes can be easily obtained by sulfonation with concentrated H2S04 (Scheme 7.11).25 This method represents a rapid and efficient way of preparing water-soluble calixarenes. 

Calixarene esters are easily available by alkylation with ethyl bromoacetate and are often used as starting materials for the introduction of chiral groups at the narrow rim. Their aminolysis by chiral amines led to chiral calixarene derivatives in high yields. Water soluble calix[4]arene amino acid derivatives 9a,b obtained in this way, were successfully used as a pseudostationary phase... 

Water-soluble calixarene derivatives have increasingly been synthesized with the aim to use them for biological and medical purposes. Here chirality is clearly one of the key factors. Strategies of combinatorial chemistry, often used in this area, may increase the number of available structures.293... 

Upper rim substitution is typically more synthetically challenging than the lower rim, but can confer very useful properties on the macrocycle. For example, water soluble / -sulfonatocalixarenes have been synthesized and found to be highly water soluble, unlike the hydrophobic p-t-butyl derivatives. The sulfonated calixarenes form a variety of metal complexes where the metal is usually bound to the sulfonato groups of the calixarene. 

Research continues into other agents, apart from surfactants (which are discussed in Chapter 6), which can enhance the solubility of dmgs. The calixarenes are another type of host, existing in a cup-shape in a rigid conformation. The 4-sulfonic calix[n]arenes can form host-guest type interactions with drugs such as nifedipine, a poorly water soluble agent, seen in Fig. 5.9. 

Ryu EH, Zhao Y (2005) Efficient synthesis of water-soluble calixarenes using click chemistry. Org Lett 7 1035-1037... 

A systematic study to design neutral, water-soluble calix[4]arenes has been carried out by Gansey et al., and this has led to the synthesis of calixarene derivatives with water solubility up to 0.3 M [80]. 

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). 

The nitrogenous base with caffeine has the larger binding constant for the porphyrin. Together with the sulfonic acid groups on the calixarene (see Fig. 7.7, no. 6), the hydrophilic amino acid-based substituents (Fig. 7.7, no. 5) make the supramolecular assembly water soluble up to 4-5 mM. Figure 7.7 shows an example of a complex that was prepared with either Co or Zn as central metal ion [44]. 

Casnati, A., Sciotto, D., and Arena, G., Water soluble calixarenes, in Calixarenes 2001, Asfari, Z., Bohmer, V., Harrowfield, J., and Vicens, J., Editors, Kluwer Academic Publishers, London, pp. 440-456, 2001. 

For macrocycles to have biological or medicinal relevance it is importance that they are water soluble or at least amphiphilic. While this property is true of some macrocycles, such as the sulphonate derivatives of calixarenes, it is most evident in the cyclic sugars, the cyclodextrins. These compounds are of great importance in supramolecular chemistry both a volume of Comprehensive Supramolecular Chemistry [1] and an entire edition of Chemical Reviews [2] are devoted to them. 

Direct synthesis of calixarenes with extended arms p-phenylcalix[4,5,6,8]arenes and their water-soluble sulfonated derivatives, M. Makha and C. L. Raston, Tetrahedron Lett., 2001, 42, 6215. 

The two calix[4]arenes, 24 and 26, are examples of useful derivatives the former binds lanthanides to form luminescent complexes, the latter, prepared from compound 25, is water soluble and crystallizes in a variety of forms, from laminates to nanospheres. Other derivatives are to be found in the literature. Simple derivatives, such as the O-alkyl compounds, are used as a basis for upper rim functionalization treatment of these compounds with nitric acid replaces the upper f-butyl groups with nitrates. Nitrocalixarenes can be reduced to the corresponding amines to generate a platform for further extension of the cavity and have been used to bind metals or small molecules. Oxa- and azacalix[3]arenes represent crown ether-calixarene hybrids and have binding modes reminiscent of both classes of molecules. Many alternative upper rim substituents can be introduced and, in the case of the azacalixarenes, the /V-substituent can easily be varied. 

In addition to calixarenes which have been made water-soluble as new inverse phase-transfer catalysts [85], novel ligands have been designed, based on a cydo-propene moiety bearing pyridyl substituents and called [hexakis(2- or 3-pyridyl) 3 -radialene] 37. A metallosupramolecular chemistry is envisioned by the authors and the solubility in water and their stability offer innovative perspectives [86]. 

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