Calixarenes lipophilic

California Technical Bulletin 133 test, 11 459 Californium (Cf), 1 463—491, 464t electronic configuration, l 474t ion type and color, l 477t metal properties of, l 482t Caliper Life Sciences, 26 976 Calixarene(s), 2 209 24 35-36, 47 crystals of, 24 53 derivatives of, 24 37 inclusion compounds in, 14 165-166 lipophilic, 24 57... 

Thus, the characteristic potentiometric selectivity of calix[6]arene hexaester 29 for primary amine guests can be reasonably interpreted on the basis of the structural factors relevant to the nonpolar moieties of guests. Such a mode of discrimination can also be achieved by a calix[6]arene hexaester with short alkyl chains [28 (R = H)]. In addition, the selectivity was found to be essentially the same in the presence or absence of lipophilic anionic site HFPB added in the membrane (Table 3). Potentiometric discrimination of protonated amines by host 28 (R = H, Bu ) as well as of aldehydes (as the protonated hydrazones generated in situ) by hosts 26 (R = Bu ) and 28 (R = H) was also reported. Recently, quantitative estimation of optical selectivities for alkali metal ions or protonated amines were made with liquid membranes containing chromogenic derivatives of calixarenes. ... 

Cascade-type binding [3.24] of anionic species occurs when a ligand first binds metal ions, which then serve as interaction sites for an anion. Such processes occur for instance in lipophilic cation-anion pairs [1.31] and with Cu(ll) complexes of bis-tren 33, of macrocyclic polyamines [3.25, 3.26] and of calixarenes [3.27]. 

It was shown that narrow-rim CMPO derivatives form stronger 1 1 lanthanide complexes than their wide-rim counterparts. However, lanthanide extraction results display a stronger extracting ability. This discrepancy can be explained by the fact that, contrary to the wide-rim CMPO calixarenes that form polymeric species, a part of less lipophilic monomeric narrow-rim CMPO calixarene piles up at the interface instead of being extracted, as predicted by Wipff for the extraction of strontium by mixed amide calixarenes (see Section 4.4.1.1). This assumption is all the more... 

The main drawback of calixarene CMPO is their low solubility in most diluents the presence of the bulky and lipophilic adamantane nuclei should improve it. 

To increase the distribution ratios, a solution of lithium nitrate 1M was used. This salt, which has a common anion with europium and americium to be extracted but a cation which is usually negligibly extracted by other calixarenes, should increase the distribution ratios according to the relation Du = A (JU "[N03- ". It seems that these calixarenes, as several nitrogen ligands do, present a certain affinity for this lithium cation. The lipophilic dicarbollide anion (BrCosan), which is known to facilitate cation extraction, was implemented and led to a strong increase of the extraction of cations from 10 3 M HN03 solutions. Under these conditions, only thiopicolinamide was not able to significantly extract trivalent actinides.187... 

In aqueous solution, water-soluble calixarenes have the potential to bind much more strongly to organic guests than in lipophilic media because of the hydrophobic effect (Section 1.9). Unfortunately, p-alkylcalixarenes are not water-soluble and must be derivatised in order to take them up into aqueous... 

The majority of the devices mentioned thus far rely on the Hofmeister series for anion selectivity. However, for anions that deviate from this series, organometallic receptors can be utilised. The type of ligand or metal centre will influence the sensor selectivity due to the characteristics of the electron acceptance of the complex. An interesting development that is being explored here is the use of calixarenes. These have previously found use as cation-selective species, but with suitable substitution are now being incorporated within anion-selective devices. Compounds suitable as receptors for halides [61],benzoate [61] and acetate [62] have been developed. Reinhoudt and his co-workers have reported the production of a POj-selective CHEMFET based on a uranyl cation immobilised within a salophene ligand (Fig. 5), which shows selectivity over more lipophilic anions such as Br" and NOj [63]. 

Other components of the design [138—142] include the choice of the crown size or even the use of open-chain metalloclefts, not necessarily polyether armed. The issue of special importance for extraction and transport applications is the selection of substituents ensuring a necessary lipo-philicity-solubility balance. For example, use of a cyclohexano moiety as shown above, instead of the more common o-phenylene bridge between nitrogens, enhances solubility in the membrane phase. The modification of the polyether chain with binaphthyl or calixarene substituents provides high membrane transport rates due to increased ionophore lipophilicity [138,142]. Some representative examples (initial fluxes, in 10 mol cm h , through o-nitrophenyloctyl ether-impregnated Accurel membrane 1 M source urea [138]) are as follows. 

Calixarenes without ionisable substituents at the wider rim are not water soluble. Their complexation behaviour towards organic cations, has, therefore, been studied mainly in lipophilic solvents such as CDCI3 and (CDCl2)2- The cation- r interaction is the main contribution to the stability of complexes and the association constants are rather low, ranging from 10 to lOOOM (see Table 12.1). 

Another interesting aspect of calixarenes is their high lipophilicity which together with their macrocyclic nature led us to use them as ordered building blocks for open chain and cyclic cation ligands, and other authors to employ them as such for the transport of alkali cations through bulk liquid membranes. 

As carriers for metal cations especially the lower rim functionalized p-rert-butylcalix[4]arenes have been used. The calixarenes la, lb with a crown-5 over two opposite aryl moieties are selective for potassium, whereas the tetraamide 2a, tetraketone 2b and tetraester 2c (Figure 1) selectively form complexes with sodium. These neutral receptors are suitable as carriers because of their high lipophilicity and complexation selectivity. 

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