Calixarene anion

ACR corresponds to the difference between the CR in the presence of the calixatene in the vesicles and the CR in the absence of the calixarene receptor (to correct for nonspecific interactions). A plot of ACR for the cationic calixarene versus ACR for the anionic calixarene gave rise to a unique diagnostic point for each protein that was examined. 

For instance, we have recently shown that the monolayer-anchored ferrocene groups are not complexed by hosts such as the anionic calixarene 9 and p-CD[31]. Presumably, these two receptors are strongly solvated in aqueous media so that their approach to the hydrophobic monolayer is unfavorable, thus preventing any significant binding. In contrast, an... 

The synthetic route to water-soluble calixarenes is illustrated in Scheme 1. In order to introduce functional groups into each benzene ring one must choose the reaction having a quantitative yield, because the isolation of a fully-substituted product from lower-substituted by-products is fairly difficult. In Scheme 1 the key step to synthesize water-soluble anionic calixarenes is the sulfonation which proceeds quantitatively under the optimized conditions. The sulfonate group was converted to the nitro group to afford 2 [4]. Finally, we obtained water-soluble cationic calixarenes, from 3 via O-alkyl-p-aminocalixarenes. 

As is widely known, the ferrocene subunit undergoes rapid monoelectronic oxidation to yield the corresponding cationic ferrocenium species. Thus, the fer-rocenium/ferrocene redox couple is electrochemically reversible and provides a convenient handle to study the complexation of the ferrocene-containing guests by the anionic calixarene host. Our experiments clearly indicate that all guests are strongly complexed by the calixarene host. For instance. Figure 1 shows the anodic voltammetric behavior of 4 in the absence and in the presence of host... 

Although attractive host-guest coulombic forces play an important role in the binding of these guests to the anionic calixarene, other interactions must be respon-... 

It is not only p-substituted phenols that have been connected by methylene groups an extended calixarene based on naphthalene units [57] has also been synthesized and its acidity constants have been measured (see Table 25 Poh and Lim, 1989, 1990). In contrast to the calix[4]arenes, the pKa of the expanded calixarene [57] did not differ much from the of the analogue [58]. This may have two explanations (i) the conformation of the expanded calixarene is different from phenol-based calix[4]arenes and a special stabilization of the anion does not occur, (ii) this stabilization occurs but it is also present in the analogue. A stabilization by the neighbouring... 

Stepwise conversion of an olefin into an alkylidene has been reported in [calixarene]W(olefin) complexes. Where the olefin was ethylene or propylene, deprotonation afforded an anionic alkylidyne species, which on protonation... 

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. ... 

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... 

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