Calixarenes functionalization

Calixarenes may also bear excimer reporter sites, although the details of signal transduction are inherently different from those of CD-based excimer chemosensors. First, unlike Schemes 7 and 8, the fluorescent monomer units are not included within the calixarene bucket. Rather, calixarene functions as only a scaffold, bearing monomer subunits. Second, analyte seldom enters the calixarene bucket. The most common design for this type of chemosensor is shown in Scheme 9. A preformed excimer is disrupted by analyte binding at the... 

Their application in the biomedical field is clearly demonstrated by the preponderance of patents as compared to publications in the field. Calixarenes functionalized at the wide rim with sulfonic acid and sulfonamide groups showed anticoagulant and antithrombotic properties, approaching the activity of heparin and coumarin, currently used as anticoagulants in antithrombotic therapy. Calixarene derivatives are also active as antiviral, antimicrobial. and antifungal agents. 

As a result of the recognition of molecules and metal ions by calixarene, functions of a higher level (secondary function) than simple binding (primary function) may arise. This can be conveniently described by a mathematical formulation as ... 

Owing to the unique host-guest properties of calixarene macrocycles, calixarene-functionalized silica particles were used as cation-selective receptor colloids [81], and separator of lanthanides and actinides [82]. Calixarenes were also used for the syntheses of Ru, Pt and Pd NPs [83-85]. Furthermore, photoluminescence and charge-transfer complexes of calixarenes and calix[4]arene-based glycoclusters were grafted onto the surface of Ti02 NPs [64, 86]. 

For other applications such as in electrokinetics or the synthesis of radiopharmaceuticals it is desirable that the calixarene-functionalized polymer be soluble in aqueous media. In order to achieve such a goal it is necessary to avoid the formation of cross-linking within the polymer. Such a polymer 12 that is soluble in aqueous or organic solvents is formed when a calixarene with a single haloalkyl substituent on the upper rim is reacted with the polyethyleneimine solution (Equation 9). 

Progress in molecular recognition of functionalized calixarenes with hetero-atomic bridges as synthetic receptors 99MI43. 

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. 

A huge group of macrocycles which contain 2,6-disubstituted phenols are the calixarenes [51]-[53]. Their conformation has been investigated intensively (Gutsche, 1989, 1991). In most conformations, however, the phenolic rings are oriented almost vertically in relation to the plane of the macrocydic ring. Therefore the OH functions are not oriented in an intra-annular fashion. Nevertheless the pK values of calixarenes [51] differ from those of other comparable phenols. The reason for this is the... 

The alkene-W complexes used in this study are complexes 33, 166, and 168 (Schemes 5 and 31). The deprotonation of the W-alkene functionality has been carried out on 166, which has three methyl substituents at the C=C bond, in order to prevent any rearrangement of the 1-metallacyclopropene to the corresponding alkylidyne.22b The reaction of 166 with LiBu led to the 1-metallacyclopropene 169 (Scheme 32), which was isolated in quite good yield. The alkylidene 169, a very stable compound, was characterized both in solution and in the solid state.28 The h NMR spectrum shows a four-fold symmetry calixarene skeleton, while the 13C NMR spectrum contains a resonance at 271.0 ppm for the alkylidene carbon. 

With the alkynyl functionality greater than two, starbust type complexes are obtained, as derived, for example, from 1,3,5-trialkynylbenzenes 85 or -triazines,86 1,1,2,2-tetraalkynylethenes,85 or bis(l,2-dialkynyl)phenylene-bridged crown ethers or calixarenes. ... 

Heteroaryl groups are present in the 4-pyridyl-ethynyl compounds81,99,100 and their extended variants with C=C-C6H4-C=C-pyr-4 ligands.81,99 These compounds can be quaternized with Mel or coordinated to a metal complex at their terminal pyridyl functions to give species addressed as molecular rods or molecular wires.81,99 Similar reactions were carried out with 3-phenanthrolinyl-ethynyl complexes,62 and special examples are also known with R based on calixarenes.51... 

Calixarenes, when in their cone-conformation (54), represent versatile host systems for metalated container molecules and many examples have been reported in the literature (55-61). Reinaud and coworkers have carried out extensive work concerned with calix[6]arenes that are functionalized at the small rim by nitrogen arms (62), aiming to reproduce the hydro-phobic binding site of mononuclear zinc and copper metalloen-zymes. A recent example is the calix[6]arene ligand L1 (Fig. 3), in which a tris(2-methylpyridyl)amine unit covalently caps the calixarene small rim (63). The ligand forms copper complexes of... 

Recent years have also seen the development of a variety of com-plexation reagents incorporating C-P bonds and their associated functionalities, such as phosphoryl linkages. For example, substituted calixarenes (Figure 1.4) have been developed for extraction of radionuclides, and phosphorus-derivatized cyclodextrins for stereospecific inclusion interactions. 

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.

PET-17 has been designed for selective recognition of sodium (Figure 10.15). It contains four carbonyl functions, two of them being linked to pyrene and nitrobenzene at opposite sites on the calixarene lower rim. Complexation with Na+ prevents close approach of pyrene and nitrobenzene and thus reduces the probability of PET. The fluorescence quantum yield increases from 0.0025 to 0.016. 

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