Calixarene • A calixarene is a macrocycle or cyclic oligomer based on a hydroxyalkylation product of a phenol and an aldehyde [1] . The word calixarene is derived from calix or chalice because this type of molecule resembles a vase and from the word arene that refers to the aromatic building block. Calixarenes have hydrophobic cavities that can hold smaller molecules or ions and belong to the class of cavitands known in Host-guest chemistry . Calixarene nomenclature is straightforward and involves counting the number of repeating units in the ring and include it in the name. A calix[4]arene has 4 units in the ring and a calix[6]arene has 6. A substituent in the meso position Rb is added to the name with a prefix C- as in C-methylcalix[6]arene.
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Calixarene A calixarene is a macrocycle or cyclic oligomer based on a hydroxyalkylation product of a phenol and an aldehyde [1]. The word calixarene is.
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Calixarene
• A calixarene is a macrocycle or cyclic oligomer based on a hydroxyalkylation product of a phenol and an
aldehyde [1]. The word calixarene is derived from calix or chalice because this type of molecule resembles a
vase and from the word arene that refers to the aromatic building block. Calixarenes have hydrophobic
cavities that can hold smaller molecules or ions and belong to the class of cavitands known in
Host-guest chemistry. Calixarene nomenclature is straightforward and involves counting the number of
repeating units in the ring and include it in the name. A calix[4]arene has 4 units in the ring and a
calix[6]arene has 6. A substituent in the meso position Rb is added to the name with a prefix C- as in C-
Amphiphilic polydedron-shaped p-sulfonatocalix[4]arene building blocks, 3, which have been previously shown to assemble into bilayers in an antiparallel fashion, have been assembled in a parallel alignment into spherical, 4, structures by the addition of pyridine N-oxide and lanthanide ions. Crystallographic studies revealed the manner in which metal ion coordination and substrate recognition direct the formation of these supramolecular assemblies. The addition of greater amounts of pyridine N-oxide changed the curvature of the the assembling surface and resulted in the formation of extended tubules.
The amount of 'chemical space' enclosed by 4 is about 1,000 Å3. This space houses 30 water molecules and two sodium ions. However, the van der Waals volume of 3 is about 11,000 Å3. 4 is differentiated from 2 by several factors. First, the supramolecular forces used to hold 2 together are hydrogen bonds, while a combination of van der Waals forces, -stacking forces, and metal ion coordinate covalent bonds is employed for 4. Second, the surface which encloses the chemical space is essentially one atom thick for 2, while it is the thickness of the p-sulfonatocalix[4]arene building block in 4 (hence, the 11,000 Å3 volume of the assembly with only 1,000 Å3 of space within). Third, the contents of the capsule are rather completely ordered for 4 (by the hydrogen bonds from the enclosed water to the phenolic oxygen atom hydrogen bond acceptors at the base of the p-sulfonatocalix[4]arene), but the contents are completely disordered for 2 (because of the lack of any directional bonding force connecting the skeleton of the assembly to the contents therein).
Applications
• Calixarenes are applied in enzyme mimetics, ion sensitive electrodes or sensors, selective membrames, non-
• Building esthetic molecules with calixarenes include thus far a molecular Football World Cup [9]
Fig. Shape relationship of the football world cup (left) with the fullerene-calix[4]arene conjugate 1 as a PM3-calculated space-<ETH>lling model (middle) and a schematic VB structure representation (right).