Calixarene derivative

Many other cyclic and noncyclic organic carriers with remarkable ion selectivities have been used successfiilly as active hosts of various liquid membrane electrodes. These include the 14-crown-4-ether for lithium (30) 16-crown-5 derivatives for sodium bis-benzo-18-crown-6 ether for cesium the ionophore ETH 1001 [(R,R)-AA -bisd l-ethoxycarbonyl)undecyl-A,yVl-4,5-tctramcthyl-3,6-dioxaoctancdiamide] for calcium the natural macrocyclics nonactin and monensin for ammonia and sodium (31), respectively the ionophore ETH 1117 for magnesium calixarene derivatives for sodium (32) and macrocyclic thioethers for mercury and silver (33). 

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]. 

He also prepared a poly(styrene-g-styrene) polymer by this technique [114], The lack of crosslinking in these systems is indeed proof of the control achieved with this technique. An eight-arm star polystyrene has also been prepared starting from a calixarene derivative under ATRP conditions [115]. On the other hand, Sawamoto and his coworkers used multifunctional chloroacetate initiator sites and mediation with Ru2+ complexes for the living free-radical polymerization of star poly(methylmethacrylate) [116,117]. More recent work by Hedrick et al. [84] has demonstrated major progress in the use of dendritic initiators [98] in combination with ATRP and other methodologies to produce a variety of structure controlled, starlike poly(methylmethacrylate). 

Cuest-Induced Changes in Membrane Permeability. Calixarene derivatives are also used for sensing systems other than ISEs or optodes. Recently, a systematic investigation on the control of membrane permeability by use of oriented monolayers composed of calixarene esters was carried out. The hosts used were short alkyl chain esters of calix[6]arene [28 (R = Bu )] and calix[4]arene [26 (R = Bu ), 30 both cone conformers]. The permeabilities through the intermo-lecular voids of these monolayers were evaluated by cyclic voltammetry, as described earlier for oriented membranes of nucleobase derivatives. Cationic, anionic, and neutral electroactive compounds were used as the permeability markers. The voltammetric measurements were carried out either for a monolayer... 

Calixarene derivatives involving crown ethers like 233 exhibit complexation ofalkali or ammonium cations typical of crown ethers that is especially effective in the partial cone conformation [26]. By a proper functionalization selective synthetic receptors for specific hosts have been developed. For instance, two 2,4-diaminotriazine groups at diametrical positions of the upper rim of a... 

Kinetic analyses allowed the experimental results to be related to the dependence of transport rates and selectivities on carrier properties [6.9, 6.17, 6.18]. Detailed studies of 8 and 9 in vesicles bore on the efficiency, the selectivity and the mechanism of the processes [6.19]. The rates of transport by proton ionizable macrocyclic carriers are pH dependent [6.12]. Diverse other ligands have been used as carriers, such as acyclic polyethers or calixarene derivatives [6.20, A.6]. 

Channel-like architectures are formed in the mesophase given by complexes of long chain crown ether derivatives [8.196a,b] and long-chain calixarene derivatives display columnar liquid-crystalline arrangements [8.196c]. Self-assembled tubular structures based on cyclic peptide components have been described [8.186]. 

The first project, gathering eight teams from six EC countries where more than 140 new extractants were prepared and studied, not counting all the precursors and intermediates. Tests carried out with these compounds on simulated and real waste showed the excellent chemical and radiolytic performance of calixarene derivatives. 

Although fluorescent calixarenes would be an appropriate section herein, especially as regards nuclear applications, the reader is referred to the recent and exhaustive review Calixarene-derived Fluorescent Probes. 85... 

The quantitation of undesired enantiomers in drug raw materials is one of the objectives of the pharmaceutical industry. Several calixarene derivatives were investigated as fluorescence sensors for chiral pharmaceutical compounds. The mechanism of these examples is based on different fluorescence quenching of the calixarenes by the two enantiomeric forms of a specific analyte. 

Ammonium cations may also be bound by cation s interactions by large cyclophanes such as 3.102 (calixarene-derivatives - see Section 3.14). The rigid, deep-cavity tetrahydroxy receptor 3.102a is able to selectively bind tetramethylammonium ions with Kn > 104 M 1 in chloroform solution,... 

Figure 14.8 Amphiphilic fullerene and calixarene derivatives with dendritic branches that form long-lived micelles (Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced by permission).

The corresponding dependence of cation complex stability on the anion differs profoundly from that of most other cation receptors such as cyclophanes or calix-arenes [16]. For these cation complex stability decreases on changing the anion from picrate through iodide to tosylate, a dependence that has been attributed to ion-pair aggregation in non-polar solvents. Because the interaction of quaternary ammonium ions with tosylate or iodide in chloroform is considerably stronger than with picrate, cation complexes in the presence of the latter anion are usually more stable. Only when iodide or tosylate cooperatively contributes to cation binding, as in 3 or in some recently described calixarene derivatives [17], is reversal of this order observed. 

In summary, our approach of using cyclopeptides with natural amino acids and 3-aminobenzoic acid subunits for the development of macrocydic receptors has afforded remarkably efficient hosts. The cation affinity of 4b, for example, exceeds that of many calixarene derivatives. Even more interesting is the high anion affinity of 5 in aqueous solution. By introdudng additional functional groups such as car-boxylates to the periphery of the cavity, we recently also obtained cydopeptides that interact with neutral substrates, for example, carbohydrates [25]. Our peptides therefore represent a versatile dass of artificial receptor that should prove useful in supramolecular and bioorganic chemistry. 

There is some evidence that particular calixarene derivatives have direct therapeutic properties. The antitubercular action of 4-octylcalix[8]arenes with pendent polyether chains was determined by Cornforth s group in the early 1950s where the compound, then of unknown composition and called Macrocyclon, was shown to be generally non-toxic to mammals and yet more potent than streptomycin in the treatment of tubercular bacilli [32],... 

The relatively low thermodynamic stability of complexes of hemicarcerands or other container-type hosts is a direct consequence of structural aspects of the walls that make up the inner surface of such compounds. These walls are lined by aromatic subunits while free electron pairs of heteroatoms such as those of the ether oxygen atoms are preferentially oriented to the outside. Complexes are therefore enthalpically stabilized only by weak dispersive interactions. In the case of positively charged guests cation-re interactions can contribute to binding enthalpy as in a self-assembled calixarene-derived capsule [9], but directed interactions such as hydrogen-bonding interactions are usually absent. 

The gadolinium complex with Cxi displays a reasonable relaxivity and it has been assessed as a potential contrast agent for magnetic resonance imaging. Its stability constant is however too low to make this complex a good candidate for in vivo applications. Until now, no calixarene derivative has proved efficient in this field, contrary to the pendant-arm substituted coronands. 

Probably the first examples of chiral calixarene derivatives were esters with camphorsulfonic acid24 derived from t-butyl-calixfSjarene.25 Later ethers obtained with (S)-2-methylbutyl bromide were synthesized and studied with respect to their CD spectra and their chiral recognition ability.26... 

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... 

Here we summarize calixarene derivatives having an n-fold molecular axis perpendicular to the molecular main plane, which is usually defined by the carbon atoms bridging the aromatic units. This includes C2-symmetrical molecules if this twofold axis is identical to the molecular axis. Some examples in which there is a twofold axis perpendicular to the molecular axis have been described above. 

In fact, as expected, the interaction of these calixarene derivatives with barbiturates e.g. 136 (or cyanurates 138) in the ratio 1 2 results in the formation of box-like assemblies consisting of nine particles (3 x 135 and 6 X 136) held together by 36 hydrogen bonds. These aggregates are stable on the NMR timescale at ambient temperature in apolar solvents such as CDC13 or toluene-d6. However,... 

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... 

Initially it was believed that this anomalous behaviour was linked to the rotation of a tetraethylammonium guest within the capsule which has been observed. This proved not to be the case, as was confirmed by the use of lower symmetry calixarene derivatives to reduce the ambiguity of the NMR spectra. Molecular dynamics calculations were employed to show that the size of the tetraethylammonium guest means that the capsule has to be significantly expanded in order for it to fit within the cavity. The result of this expansion is that the ureas are only... 

The selectivities of Cs+ ISEs based on dibenzo-18-crown-6 derivatives <1986FZA241> or 2,3-benzoquinone 15-crown-5 ethers <1996AN127> are of limited interest, because they are not dissimilar to those found with iono-phore-free ion-exchanger ISEs < 1977ANA399>. Nowadays, the best Cs+ selectivities are obtained by using calixarene-derived crown ethers . 

---