Calixarenes maxima

Selective extraction experiments were then performed to see transference of some transition elements (Cu ", Ni ", Co ", and Fe " ) from the aqueous phase to the organic phase by the synthesized polymeric calixarenes. Phase-transfer studies in water-chloroform confirmed that polymer 2b and 3b were Fe ion-selective as was its monomer (1). Extraction of Fe " cation with 2b and 3b was observed to be maximum at pH 5.4. Only trace amounts of other metal cations such as Cu, Ni ", and Co " were transferred from the aqueous to the organic phase (Table 3). Furthermore, the extracted quantities of these cations remained unaffected with increasing pH. The effect of pH on the extraction of 3b was lower and 56% extraction was accomplished even at pH 2.2. The extraction experiments were also performed with calix[4]arene (1) the ratio was 8.4% at pH 2.2. The polymeric calix[4]arenes were selective to extract Fe " from an aqueous solution, which contained Cu +, Ni, Co ", and Fe " cations, and it was observed that the... 

Complexation studies were carried out by electrospray ionization mass spectrometry (ESI-MS) with three lanthanides (La, Eu, and Yr) at a concentration of 10 4 M, while the ratio of concentration of CPw2 versus calixarene (r = [calix]org/[Ln]aq) was varied between 0.1 and 10.165 The behavior of the three lanthanides is the same the 1 1 Ln calix-CMPO complex is always predominant in the range of concentration studied the 2 1 Ln calix-CMPO appears in the case of metal excess with a maximum for r = 0.5, while the percent of 1 2 Ln calix-CMPO increases as the concentration of ligand increases, but does not exceed 10% for r = 10. These studies show that two factors play a key role in the selectivity of CMPO derivatives, firstly the presence of phenyl groups on the phosphorus atom, which confers the selectivity to CMPO ligands, secondly the calixarene structure, which amplifies this selectivity due to its preorganization. Indeed the noncyclic derivative (Os2), in spite of the presence of phenyl units, does not display noticeable selectivity. 

Water-soluble calix[n]arenes 20-24 with sulfonated fragments 4-6 aromatic rings) and aminomethylated calix[4]arenes were used as components in the catalytic system for the cross-coupling reactions of l-iodo-4-phenylbenzene and phenylboronic acid (Suzuki reaction) catalyzed by palladium complexes with sulfonated triphenylphosphine (Scheme 4.13) [65], Addition of water-soluble calixarenes increased the yield of reaction products more than twofold. The maximum activity was exhibited by calixarenes containing amino groups 22-24. The appropriate constants of the formation of respective inclusion complexes were significantly higher. 

Calixarenes have been used to spatially arrange glycoclusters in a defined predictable way (Fig. 24.34). Covalent attachment of small oligraiucleotides allowed hybridization of these recognition elements for lectins on solid support (DNA chips). FRET experiments indeed demonstrated that the spatial arrangement is more important than the number of galactose residues to reach maximum lectin affinity [102]. 

Surfactants based on calixarenes are ideally suited for mediating NP self-assembly, for the reasons described above. In the case of the resorcinarene framework, the four hydrocarbon tails on each macrocyclic headgroup are grafted several angstroms apart, which ensures a high degree of conformational freedom per chain in the surfactant monolayer, even at maximum packing density on the NP surface (cf. Fig. 34.7). 

For comparison purposes, lifetimes of about 80 microseconds were determined for the calixarene inclusion [10, 11] and 3.1 milliseconds for inclusion into the narrower channels of silicalite [12, 18], as compared to about 40 microseconds for benzophenone microcrystals, all determined at the maximum emission wavelength (about 448 nm) [14]. 

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