Sulfonated calix arenes

M. Vazquez, J. Bobacka, M. Luostarinen, K. Rissanen, A. Lewenstam, and A. Ivaska, Potentiometric sensors based on poly(3,4-ethylenedioxythiophene) (PEDOT) doped with sulfonated calix[4]arene and calix[4]resorcarenes. J. Solid State Electrochem. 9, 312-319 (2005). 

The sulfonated calix[8]arene 27 (Structures 8), which can be viewed as a simplified y-CD with the carbohydrate backbone replaced by an aryl moiety, mimicked heparin in the stimulation of heparan sulfate synthesis from cultured endothelial cells [62]. 

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. 

Calixarene 8 acted as a weak catalyst, whereas the compound 9 catalyzed fivefold more effectively than sodium dodecylsulfate. The compounds 10 and 11 with acidic protons were found to be extremely effective catalysts. The dependence of the observed reaction rate constants on concentration had a plateau typical for catalytic reactions in micellar media. Thus, p-sulfonate calix[6] arenes mimic the function of glyceraldehyde-3-phosphate dehydrogenase [55]. 

Catalytic systems comprising of sulfonated calix[n]arenes with alkyl group at the lower rim (n = 4, 6) and scandium inflate were used for the Mukaiyama aldol addition (Scheme 4.14). It was established that cahxarenes stabilized labile silyl enol ester and allowed reaction to be carried out in water [66]. 

A remarkable stabilizing effect of rhodium on the hydrolysis rate of a cage monophosphite derived from sulfonated calix[4]arene was observed by Cobley and Pringle [175]. The phosphite has a life in water of only 5 h. However, coordination to Rh enhanced its stability toward hydrolysis to 4 months. Consequently, it survived even the conditions of an aqueous two-phase hydroformylation. 

Inclusion of Solvent Violet 9 inside sulfonated calix[4—6]arenes was employed for altering its interaction with DNA [106]. Supramolecular complexes between calixarenes and nucleobases were formed as single cocrystals and shown to confine the nucleic bases inside self-assembled calixarene containers [107]. 

Some of calix[ ]arene sulfonic acids were also developed as Bronsted acid catalysts for Mannich-type reactions [23]. Because of their water-solubility, the reaction can be performed in water with obvious advantages from an environmentally point of view. As depicted in Fig. 27.8, two water soluble calixarene bearing a sulphonic acid group are suitably employed in the Mannich reaction in water as a catalyst. 

Thanks to the versatility of the Raman spectroscopy, nanoparticles AgNP(25) were used also to detect other policyclic aromatic pollutants (PAHs), like benzo [cjphenanthrene, triphenylene, and coronene [67]. In this case, selectivity is not as important as in other sensors, because the pollutant molecule can be in principle identified by its Raman spectrum. The affinity constants and the limits of detection of PAHs were also determined. In 2012, Coleman and co-workers developed a method to determine the critical micellar concentration (CMC) of cationic surfactants exploiting the SPB of a series of sulfonato calix [njarene-capped AgNPs [68]. The nanoparticles were synthesized by reducing AgNOs with sodium borohydride in aqueous solution in the presence of the sulfonate calix[n]arene derivatives 24, 26 and 27 (see Fig. 35.15) and characterized by TEM, DLS and UV-visible spectroscopy. Suspensions of the... 

Water-soluble phosphate ligands have also been explored. A rhodium complex containing sulfonated calix [4]arene (4) was reported to be sufficiently stable in water and allowed water/toluene biphasic hydroformylation of methyl 3-pentenoate (Scheme 6.2), giving rise to a branched aldehyde as the only product in 46% yield at 95% conversion at 60 °C after 3h. Moreover, the branched aldehyde was hydrogenated and then lactonized to give a lactone [21]. 

Yosida et al. [41] found that p-t< rr-butylcalix[6]ar-ene can extract Cu from the alkaline-ammonia solution to the organic solvent. Nagasaki and Shinkai [42] described the synthesis of carboxyl, derivatives of calix-[n]arenes ( = 4 and 6) and their selective extraction capacity of transition metal cations from aqueous phase to the organic phase. Gutsche and Nam [43] have synthesized various substituted calix[n]arenes and examined the complexes of the p-bromo benzene sulfonate of p-(2-aminoethyl)calix[4]arene with Ni, Cu , Co-, and Fe. ... 

The specific structure of [(H20)5Ni(py)]2+ was observed in the complexes with the second-sphere coordination of calix[4]arene sulfonate.715 There are two different [(H20)5Ni(py)]2+ cations in the complex assembly. In one the hydrophobic pyridine ring is buried in the hydrophobic cavity of the calixarene with the depth of penetration into the calixarene cavity being 4.3 A (Figure 9). The second independent [(H20)5Ni(py)]2+ cation is intercalated into the calixarene bilayer. 

Figure 9 Complex assembly of [(H20)5Ni(py)]2+ and calix[4]arene sulfonate.715...

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]. 

Calixarene-based M5 [calix[4]arene sulfonates] vH20 (M = Na x= 12) K (v = 8) Rb (x = 5) Cs (x = 4J) have been used to construct supramolecular assemblies. They have been structurally characterized, and exist as bilayers of anionic truncated pyramids in the cone configuration ... 

A number of other types of calixarene esters are known, including the aryl-sulfonates (often used to establish the calix[4]arenes in the cone conforma-tion ), phosphates (often used as intermediates in the replacement of the OH groups with and phosphonates. ... 

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