Calix arene receptor

During the last fifteen years, a great deal of effort have been devoted to the synthesis of suitable calix[ ]arene receptors for lanthanide ions, mainly with the purpose of developing... 

Cobaltocenium calix[4]arene receptors, characteristics, 12,475 Cobaltocenium-metallacarborane salts, preparation, 3, 23 Cobaltocenium receptors, characteristics, 12, 474 Cobalt phosphines, as supports, 12, 683 Cobalt-platinum nanoparticles, preparation, 12, 74 Cobalt-ruthenium clusters, as heterogeneous catalyst precursors, 12, 768... 

Diamond and coworkers attribute an increase in fluorescence from the anthracene reporter sites of 44 to the increased rigidity induced by complexation of Li+, Na+, and K+ to the calixarene s tetraester cleft. The tetraamide derivative, 45, shows an especially selective response to Na+ ion [383], Restricted motion of the calix[4]arene is believed to lead to the enhanced luminescence response. This contention is supported by H NMR studies, which show metal ions to confer significant order on the calix[4]arene receptor. 

The Re(I) bipyridyl unit has been exploited in another series of ion-pair sensors. Molecules 61-64 incorporate crown ether components to act as cation receptors [43,44]. H NMR titrations revealed 61-64 to be selective for acetate over chloride. In all the receptors (except 62 and 64 with acetate) enhanced binding was observed in the presence of K+ cations. The degree of enhancement is lower in the xylyl-spaced molecules 62 and 64 (40-50%) than in 61 and 63 (80-110%). It is also small compared to that seen in the calix[4]arene receptor 60. 

Calix[ ]arenes are a family of macrocycles prepared by condensation reactions between n /v/ra-substituted phenols and n formaldehyde molecules under either base or acid catalysis. Different sizes of the macrocycles can be obtained (n = 4-20) (Stewart and Gutsche, 1999) depending on the exact experimental conditions, which were mastered in the 1960 s (Gutsche, 1998), but the most common receptors are those with n =4,6,8 (macrocycles with an odd number of phenol units are more difficult to synthesize). We use here the simplified nomenclature in which the number of phenolic units is indicated between square brackets and para substituents are listed first.4 Calixarenes, which can be easily derivatized both on the para positions of the phenolic units and on the hydroxyl groups, have been primarily developed for catalytic processes and as biomimics, but it was soon realized that they can also easily encapsulate metal ions and the first complexes with d-transition metal ions were isolated in the mid-1980 s (Olmstead et al., 1985). Jack Harrowfield characterized the first lanthanide complex with a calixarene in 1987, a bimetallic europium complex with p-terf-butylcalix[8]arene (Furphy etal., 1987). 

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. 

Figure 13. Crystal structure of cobaltocenium functionalized calix[4]arene receptor 103. Acetonitrile is incorporated in the crystal structure. [Reprinted from reference 219]...

Calixarenes have attracted the attention of a number of groups for constructing a wide variety of receptors. Functionalized higher calix[ ]arenes ( = 6 and 8) are also being increasingly synthesized. 

Beer et al. have constructed a bipyridylruthenium(II) calix[4]arene receptor (Figure 51) for anion recognition [72]. Electrochemical studies showed this receptor to recognize H2PO4 in the presence of a 10-fold excess of bisulfate or chloride. 

Figure 51 A bipyridylruthenium(II) calix[4]arene receptor for anions [72]...

Calix[n]arenes are cyclic condensation products of para-substituted phenol derivatives and formaldehyde [29], They are highly interesting for the development of sensitive coatings due to their conformational flexibility and the ease by which they may be modified chemically. Chemical modification can be done either in the meta position, or by reactions at the hydroxy group. In this way, bulky substituents [30], chelating substituents [31], aromatic residues [32], crown ethers [33,34], peptides [35,36], etc. can be introduced. A first approach to combinatorial synthesis of calix[4]arene receptors has been published by Reinhoudt and co-workers [37,38], who prepared calixarenes with different substituents. In solution, these calixarenes lead to formation of hetero-oligomers with barbiturates, and these hetero-oligomers were detected by MALDI-TOF mass spectrometry and H-NMR spectroscopy. 

Baur. M. Frank. M. Schatz, J. Schildbach. F. Water-soluble calix[ ]arenes as receptor molecules for non-polar... 

Beer. P.D. Hesek. D. Nam. K.C. Drew. M.G.B. Anion recognition properties of new upper-rim cobaltocenium calix[4]arene receptors. Organometallics 1999. IS. 3933-3943. 

Calix[6]arene receptors 53a-d, bearing additional car-boxy groups in the 6-positions of the picolinamide nuclei, showed a remarkable efficiency of extraction of both Eu and Am + ions even at very high nitric acid concentration. Indeed receptors 53c-d are effective even at 3M HNO3 concentration and are more efficient than 51a for instance, at [H+] = 0.1 M, Dm for 53c are 6 order of magnitude higher than those for 51a. ... 

A calix[4]arene receptor featuring both a cation-binding site in the form of ether/amide functionality and an anionbinding site in the form of a bisthiourea together on the lower (narrow) rim of the calixarene scaffold was reported by Kilbum in 2003. ... 

Metal-based nanoparticles decorated with calix[4]arene receptors to sense polycyclic aromatic hydrocarbons (PAHs) have been developed by Sanchez-Cortes [ 145]. Each combination of host and PAH (pyrene, triphenylene, benzo[c] phenanthrene, coronene) gave a different signature in their surface-enhanced Raman scattering spectra, thus offering valuable information on the interaction between the calix[4]arene receptors and the PAH molecules. 

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