Calixarenes forms

Two calix[4](diseleno)crown ethers were synthesized by the treatment of the disodium salt of 1,3-propanediselanol with preorganized 1,3-dibromoethoxycalixarenes the 1,3-Se-bridged calixarene forms an infinite sheet aggregate by means of self-inclusion and intermolecular Se—Se interactions in the solid state <02TL131>. 

Upper rim substitution is typically more synthetically challenging than the lower rim, but can confer very useful properties on the macrocycle. For example, water soluble / -sulfonatocalixarenes have been synthesized and found to be highly water soluble, unlike the hydrophobic p-t-butyl derivatives. The sulfonated calixarenes form a variety of metal complexes where the metal is usually bound to the sulfonato groups of the calixarene. 

Since the calixarenes form complexes with a variety of guests (see Chapter 5) it is not surprising that their conformational mobility is influenced by cations. 

Figure 4.6.1 Amphiphilic calixarenes form monolayers on tin oxide electrodes, which then differentiate between water-dissolved monosaccharides (from left to right ribose, galactose, glucose).

Many calixarenes form complexes in the solid state, this property having been observed even before the structure of compounds was established. Among the simple ca-lix[n]arenes, for example, / >-rer/-butylcalix[4]arene forms complexes with chloroform, benzene, toluene, xylene, nitrobenzene, nitromethane, acetonitrile, and many others, while /r-rer/-butylcalix[5]arene complexes were studied with lower alcohols, ethyl acetate, toluene, and tetraline. More flexible / -terr-butylcalix[6]arene was found to form complexes with acetonitrile and / -rerr-butylcalix[8]arene with chloroform. The tenacity with which the guest molecule is held by the calixarene hosts varies widely with the size of macrocycle. Whereas tetramers to hex-... 

These calixarenes form 2 1 complexes with C60 and include = benzyl. = for which the complex was structurally authenticated (see above) R = 4-pyridyl, R = CH2C(0)0Et, which can be assembled with Pd via pyridyl complexation into hexacationic capsules confining C60 (NMR studies) and R = Bu = water-solubiliz-... 

The functionalization of phenolic groups with trimethylsilyl moieties is a similar type of modification and produces useful precursors for further transformation [188, 188a, 189], Thus, silylated calixarenes form subvalent germanimn and tin complexes [189a]. 

Chlorhexidine forms an inclusion complex with para-sulphonatocalix[4]arene. I this complex chlorhexidine adopts V-shaped conformation (Fig. 38.8a). Two other derivatives of cahx[4]arene, i.e. the dimethoxycarboxylic acid and dihydroxyphosphonic acid which are derivatized on lower rim the calixarenes form inclusion dimers and their internal cavities are protected against inclusion of guest molecule (Fig. 38.8b, c). The co-crystals are formed instead and the chlorhexidine molecule adopts S and Z-shaped conformations, respectively. This may suggest that the conformation of guest molecule may be controlled by appropriate selection of host molecule. 

We have demonstrated for the first time that the derivatives of the spherand-type calixarenes formed by alkylation with ethyl bromoacetate give ionophores with promising complexation properties and interesting stereochemistry. While to date... 

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