Bridged calixarenes calix arene

The preorganization of the receptor molecule by introduction of an ethyleneoxy bridge imit at the upper rim was also described [131]. The cavities of these bridged calixarenes (27) were larger than the lower rim bridged calixarenes and extraction experiments were done with both solid alkali metal and ammonium picrates into chloroform. The measurements showed that these calixarenes have a lower affinity for alkali metal ions (extraction <3%) than the lower rim bridged calix[4]arenes. However, primary ammonium ions were efficiently extracted with efficiencies of 27-57%,... 

Zhou et al. [180] used a laboratory-made fiber with 25,27-dihydroxy-26,28-oxy (2, 7 -dioxo-3, 6 -diazaoctyl)oxy-p-ferf-butylcalix[4]arene/hydroxy-terminated silicone oil (amide bridged-C[4]/OH-TSO) coating in headspace SPME coupled to GC-EID for the determination of phenolic compoimds in wastewater matrices. They have compared the extraction ability of this new fiber with the commercially available polyacrylate (PA, 85 xm) fiber. They showed that the new calixarene fiber had high affinity for the phenolic compounds due to the introduction of the polar amide bridge in calix[4]arene. The authors have applied the method to determine the phenolic analytes in real wastewater samples and found recoveries ranging from 89.7% to 103.2%. 

The crown ether bridge in calix[4]arene 19 freezes the calixarene stmcture in a rigid flattened-cone conformation also pushing the two metal ions apart. The bimetallic complex 19—Zu2 cleaves HPNP eight times less effectively than the flexible 2—Zu2 [17], thus confirming that a certain degree of flexibility is beneficial and is an important requisite in a supramolecular catalyst. 

Abstract. The synthesis of 1,2- and l,3-calix[4]-Z w-crowns, double calix[4]arenes and double calixcrowns have been shown to depend on the reaction conditions (nature of the base, structure of the ditosylates, and the stoichiometry of the reactants). The 1,3-altemate conformation of the 1,3-calix[4]- w-crowns was shown to be favourable to the selective complexation of cesium cation. The observed Na /Cs selectivity was exploited in separation processes using them as carriers in transport through supported liquid membranes (SLMs). The best Na "/Cs selectivity (1/45 000) was observed for the naphthyl derivative 7. Calix(aza)crowns and 1,3-calix[4]-/ w-(aza)-crowns were also produced through the preliminary formation of the Schiff base-calixarenes, which were further hydrogenated. The syntheses consisted of the 1,3-selective alkylation of calixarenes followed by cyclization into a 1,3-bridged calixarene or by the direct 1,3-capping of the calixarene with appropriate ditosylates. Soft metal complexation by these ligands is also presented. 

Harrowfield et al. [37-39] have described the structures of several dimethyl sulfoxide adducts of homo bimetallic complexes of rare earth metal cations with p-/e rt-butyl calix[8]arene and i /i-ferrocene derivatives of bridged calix[4]arenes. Ludwing et al. [40] described the solvent extraction behavior of three calixarene-type cyclophanes toward trivalent lanthanides La (Ln = La, Nd, Eu, Er, and Yb). By using p-tert-huty ca-lix[6Jarene hexacarboxylic acid, the lanthanides were extracted from the aqueous phase at pH 2-3.5. The ex-tractability is Nb, Eu > La > Er > Yb. 

In contrast, porphyrinogens 16 (Fig. 5) possess only 16 Ti-electrons and as a consequence the delocalization over the whole macrocycle is absent. The conformations of porphyrinogens are not planar any more and can approximate to the conformations known for calix[4]arenes (vide supra). Compounds 16 (Fig. 5) may, therefore, be considered as heteroatomic calixarene derivatives, of which some have additional heteroatoms in the bridging positions [15, 28-30]. 

A new type of calixarene-capped calixpyrrole (9) has been generated (32 %) in one-step from p-fe/t-butylcalix[4]arene tetramethylketone as the template <96TL7881>. A cylindrical calix[4]-fois-cryptand, in which the central calix[4]arene possesses two 1,3-altemating diaza-tetraoxa macrocycles on each face, has been synthesized <96TL8747>. A series of substituted l,4-(2,6-pyridino)-bridged calix[6]arenes has prepared and studied <96LA1367>. 

Calix[4]arenes are characterized by a three-dimensional basket shape, the internal volume being around 10 nm3. Calixarenes exist in different chemical conformations because rotation around the methylene bridge is possible. In calix[4]arene, four conformations are possible cone, partial cone, 1,2-altemate, and 1,3-altemate. These four conformations are in dynamic equilibrium. Conformations can be locked, for instance, by placing a bulkier substituent than the ethyl group on the lower (or narrow) rim, this chain prevents the benzene units from rotating inside the calixarene cavity. 

To improve the photophysical properties of the calixarene receptors, the team of D. Rein-houdt has covalently grafted one adequate chromophore, fluorescein, on the narrower rim of calix[4]arene via either a propyl (Hs43a) or a hexyl (H543b) bridge simultaneously strongly... 

The annelated calixarene 57 may be regarded as an example for an AABC-type calix[4]arene, where the ring inversion is impossible due to the connection of the two A units by a bridge in p-position by which a second calix[4]arene system is created.117... 

Interest in phosphorus-containing calixarenes continues. Structures reported include hexa(diethoxyphosphoryloxy)calix[6]arene (8), inherently chiral 1,2-bridged calix[4]arene diphosphates, and a calixarene like C3 symmetric receptor with a phosphate function at the cavity bottom. " The purification of phosphate substituted calixarenes has been studied by chiral HPLC and by normal reverse phase HPLC. Mono(6-0-diphenoxyphosphoryl)-P-cyclodextrin (9) and mono(6-0-ethoxyhydroxyphosphoryl)-p-cyclodextrin (10) have been synthesised and show enantioselective inclusion of D and L amino acids e.g. 3.6 for D/L serine in the case of 9). ... 

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