Calixarenes esters

Kimura and coworkers [17], Diamond [18], and Damien et al. [19] have described that the polymeric calix-[4]arenes have been used as ionophores in ion selective electrodes for Na (based on calixarene esters and amides) and for Na and Cs (based on p-alkylcalixarene acetates). The electrodes are stated to function as poten-tiometric sensors as well, having good selectivity for primary ion, virtually no response to divalent cations, and being stable over a wide pH range. 

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 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... 

The formation of calixarene esters and ethers can be complicated by the problem of incomplete derivatization, as noted above, and also by the fact that conformational fixing generally occurs in the case of the calix[4]arenes. The consequences of the latter are discussed in Section 5.2. 

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. ... 

Kane. P. Kincaid, K. Fayne, D. Diamond. D. McKervey, M.A. Modelling metal complexes of calixarene esters and phosphine oxides using molecular mechanics. J. Mol. Model. 2000. 6. 272-281. 

In an attempt to mimic the highly sophisticated ion transport properties found in biological membranes for the development of an ion channel sensor, a comprehensive study on artificial systems was carried out [10]. It was shown that the permeability of orientated monolayers of various calixarene esters is strongly influenced by the complexation with metal ions [11]. It was reported that the membrane permeability of calix[6]arene esters for a neutral redox-active... 

Another application of polymeric calixarene is shown in paper [12], in which the polymer calixarene ester 14 (Fig. 14) is used as the a chemically-modified electrode for voltameric analysis of Pb(II), Cu and Hg(II) ions in dilute aqueous solutions. 

McKervey [7] and Chang and Cho [9] carried out similar studies. They prepared various ester derivatives of calixarene and tested their ion carrying capacities (Scheme 1). 

Chang and coworkers [10] have synthesized amide derivatives of calixarenes and examined their ion binding properties with Group I and Group II cations. They observed that although the amides are much less effective than the esters for the complexation of Group I cations they are more effective for Group II cations. 

Calixarenes, which are macrocyclic compounds, are one of the best building blocks to design molecular hosts in supramolecular chemistry [158]. Synthesis of calix[4]arenes, which have been adamantylated, has been reported [105, 109]. In calix[4]arenes, adamantane or its ester/carboxylic acid derivatives were introduced as substituents (Fig. 29). The purpose of this synthesis was to learn how to employ the flexible chemistry of adamantane in order to construct different kinds of molecular hosts. The X-ray structure analysis of p-(l-adamantyl)thiacalix[4]arene [109] demonstrated that it contained four CHCI3 molecules, one of which was located inside the host molecule cavity, and the host molecule assumed the cone-like conformational shape (Fig. 30). 

Macrocycles containing isoxazoline or isoxazole ring systems, potential receptors in host—guest chemistry, have been prepared by multiple (double, triple or quadruple) 1,3-dipolar cycloadditions of nitrile oxides, (prepared in situ from hydroxamoyl chlorides) to bifunctional calixarenes, ethylene glycols, or silanes containing unsaturated ester or alkene moieties (453). This one-pot synthetic method has been readily extended to the preparation of different types of macrocycles such as cyclophanes, bis-calix[4]arenes and sila-macrocycles. The ring size of macrocycles can be controlled by appropriate choices of the nitrile oxide precursors and the bifunctional dipolarophiles. Multiple cycloadditive macrocy-clization is a potentially useful method for the synthesis of macrocycles. 

Figure 5. Top Tetraurea calixarene monomers 37 and 38 bearing chiral amino acid ester residues (isoleucine and valine methyl esters, respectively) attached to the urea functions. Norcamphor 39 was the chiral guest used to detect the chirality transfer from the outside to the inner cavity.

Diethyl phosphate esters of the sterically congested phenols of calixarenes have been prepared in acceptable yields (>55%) and used in the preparation of meta-cyclophanes [8]. The corresponding reaction using diethyl phosphite, with triethylamine in place of the quaternary ammonium catalyst, results in only partial phosphorylation of the hydroxyl groups. 

Several classes of synthesized calixarenes bearing several moieties (ether, ester, and amide derivatives), were tested for the extraction of strontium picrates (from aqueous solutions into dichloromethane).128 Only a few of them show appreciable extraction levels. The p-i-butyl calix[6]arene hexa(di-/V-ethyl)amide (CA4) shows a very high extraction level of alkaline earth cations with respect to alkali metal cations. Moreover, dealkylation of the calix[6]arene hcxa(di-/V-cthyl)amidc (CA5) decreases the extraction of both sodium and strontium. As this decrease is much more important for sodium than for strontium, the Sr/Na selectivity, which increases from 3.12 to 9.4, is better than that achieved for DC18 derivative under the same conditions (8.7). These results were confirmed by extraction of strontium (5 x 10 4 M) from 1 M HN03 solutions, where it was found that p-t-butyl calix[4]arene tetra(di-N-ethyl) amide (CA2) (10 2 M in NPOE) extracts only sodium (DNa = 12.3, DSl < 0.001). 

Recently the separation of enantiomers by RIfS and SPR using calixarenes with chiral amide residues was demonstrated [19]. Chirasil-Calix (Fig. 7) is well known from capillary GC as a stationary-phase material because of its good thermal and long-term stability. The separation of amino acid derivatives and lactic esters was widely studied [23]. 

Following this same approach, Jin and coworkers have prepared a nearly identical pyrene-modified calixarene, 38, where the methoxy groups are replaced by ester functionalities [377], Na+ and K+ ions perturb the relative intensities of excimer and monomer emission in much the same manner as 37. Unlike 37, however, 38 is not sensitive to Li+ ion. 

The chiral cavitands 3.109 have been developed by combining the amino acid residue L-alanine with macrocyclic cavitands (calixarenes - Section 3.14).51 These ammonium ion receptors are able to complex a range of amino acids and their methylester hydrochloride salts, all of which contain an -NH3+ functionality capable of interaction with the carboxylate residues of the host. In general amino acids are bound only very weakly in aqueous solution, while association constants with the chiral methyl esters range from 620 M-1 for L-tryptophan methylester to 110 M-1 for L-alanine methylester. The methylester of glycine is not bound at all. Receptors related to 3.109 with variable four peptide loops arrayed around a central calixarene core have been used to bind to the surfaces of proteins. The... 

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