A calixarene is a
macrocycleor cyclic oligomerbased on a hydroxyalkylationproduct of a phenoland an aldehyde . The word calixarene is derived from calix or chalice because this type of molecule resembles a vase and from the word arenethat refers to the aromatic building block. Calixarenes have hydrophobiccavities 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  arene has 4 units in the ring and a calix  arene has 6. A substituentin the meso positionRb is added to the name with a prefix C- as in C-methylcalix  arene.
The aromatic components are derived from
phenol, resorcinolor pyrogallol, For phenol, the aldehyde most often used is simply formaldehyde, while larger aldehydes ( acetaldehyde, or larger) are generally required in condensation reactions with resorcinol and pyrogallol. The chemical reactionranks under electrophilic aromatic substitutions followed by an eliminationof water and then a second aromatic substitution. The reaction is acidcatalysed or base catalysed. Calixarenes are difficult to produce because it is all too easy to end up with complex mixtures of linear and cyclic oligomers with different numbers of repeating units. With finely tuned starting materials and reaction conditions synthesis can also be surprisingly easy. In 2005, research produced a pyrogallol  arene by simply mixing a solvent-freedispersion of isovaleraldehydewith pyrogallol and a catalytic amount of "p"-toluenesulfonic acid in a mortar and pestle . Calixarenes as parent compounds are sparingly soluble and are high melting crystalline solids  .
Calixarenes are characterised by a three-dimensional basket, cup or bucket shape. In calix  arenes the internal
volumeis around 10 cubic nanometers. Calixarenes are characterised by a wide upper rim and a narrow lower rim and a central annulus. With phenol as a starting material the 4 hydroxylgroups are intrannular on the lower rim. In a resorcin  arene 8 hydroxyl groups are placed extraannular on the upper ring. Calixarenes exist in different chemical conformations because rotation around the methylene bridge is not difficult. In calix  arene 4 up-down conformations exist: cone ( point groupC2v,C4v), partial cone Cs, 1,2 alternate C2h and 1,3 alternate D2d. The 4 hydroxyl groups interact by hydrogen bonding and stabilize the cone conformation. This conformation is in dymamic equilibrium with the other conformations. Conformations can be locked in place with proper substituents replacing the hydroxyl groups which increase the rotational barrier. Alternatively placing a bulky substituent on the upper rim also locks a conformation. The calixarene based on p-tert-butyl phenolis also a cone [http://www.iupac.org/publications/pac/1993/pdf/6503x0387.pdf] .
Adolf von Baeyerpioneered the chemistry of calixarenes although he was unable to determine its structure and did not realise its potential (he was pursuing dyes). In 1872 he mixed benzaldehydewith pyrogalloland a strong acidand noted a red-brown resinwith a marked viscosityincrease. He also used resorcinoland formaldehydewhich he had to prepare from iodoformhimself because a commercial grade of formaldehyde at that time had not been realised yet. In 1894 the Lederer-Manasse hydroxyalkylationwas invented as a synthetic tool for the preparation of hydroxylmethyl phenols, bringing calixarenes one step closer. In 1902 Leo Baekelandmade phenol formaldehyde resins a commercial success under the trade name Bakelite. In these resins phenol and formaldehyde are exhaustively condensed with each other to form heavily cross-linked polymers. The first attempt to control the reaction was made by Alois Zinke and Erich Ziegler in 1942. They employed para substituted phenols which inhibits crosslinking and should result in a linear polymer with formaldehyde. So in 1944 p-tert-butyl phenolwith formaldehyde and sodium hydroxidein linseed oilas a solvent produced for the first time a crystalline solid with a high melting point rather than a resin. In the same year another duo by the names of Niederl and Vogel did something similar with a para substituted resorcinoland they were the first to postulate a cyclic tetramer. In these days structure elucidation was limited to determination of molar massby freezing-point depressionand functional groupanalysis. John Cornforthwas in 1955 the first to realize the potential of calixarenes as a basket analogue to enzymes and repeated the work done by Zinke. he obtained a mixture of products and elicited the services of Dorothy Crowfoot Hodgkinfor structure elucidation by X-ray crystallographybut with limited success. First commercial success came to calixarenes in the nineteen fifties when the company Petrolitestarted a range of calixarene products as demulsifiers user in the oil industry.
The word calixarene was coined by David Gutsche [http://www.chm.tcu.edu/gutsche.htm] in 1975 who was also interested in this type of compound as
biomimetic, since the molecule resembled the " calyx krater" vases of ancient Greece. It was by then established that unmodified calixarenes exhibit extensive conformational mobility so that the basket was not much of a basket after all. Donald J. Cramfixed this shortcoming by inventing a way of immobilizing calixarenes. He was able to freeze in a conformation by so called lower rim functionalization, replacing the hydroxylgroups by larger substituents. The acetatecalixarene fixates the molecule as a partial cone, whereas the carbonate esteryields the full cone.
Host guest interactions
Calixarenes are efficient
sodium ionophores and are applied as such in chemical sensors. With the right chemistry these molecules exhibit great selectivity towards other cations. Calixarenes are used in commercial applications as sodium selective electrodes for the measurement of sodium levels in blood. Calixarenes also form complexes with cadmium, lead, lanthanides and actinides. [http://www.chem.ox.ac.uk/icl/beergroup/calixarene.htm] Calix  arene and the C70 fullerenein "p"-xylene form a ball-and-socket supramolecular complex. [http://www.rsc.org/publishing/journals/CC/article.asp?doi=b306411p] calixarenes also form exo-calix ammonium salts with aliphatic amines such as piperidine. 
Molecular self-assemblyof resorcinarenes and pyrogallolarenes lead to larger supramolecular assemblies[http://www.chem.missouri.edu/faculty/Atwood/research.html] . Both in the crystalline state and in solution, they are known to form hexamers that are akin to certain Archimedean solids with an internal volume of around one cubic nanometer(nanocapsules). (Isobutylpyrogallol  arene)6 is held together by 48 intermolecularhydrogen bonds. The remaining 24 hydrogen bonds are intramolecular. The cavity is filled by a number of solvent molecules. 
Calixarenes are applied in enzyme mimetics, ion sensitive electrodes or sensors, selective membrames, non-linear optics [http://www.rsc.org/publishing/journals/CC/article.asp?doi=b502045j] and in
HPLCstationary phase [http://www.chromtech.net.au/grom-calixarene.cfm] . In addition, in nanotechnologycalixarenes are used as negative resistfor high-resolution electron beam lithography[http://dx.doi.org/10.1063/1.115958] .
A tetrathia  arene is found to mimic
aquaporinproteins  . This calixarene adopts a 1,3-alternate conformation (methoxy groups populate the lower ring) and water is not contained in the basket but grabbed by two opposing tert-butylgroups on the outer rim in a pincer. The nonporous and hydrophobiccrystals are soaked in water for 8 hours in which time the calixarene:water ratio nevertheless acquires the value of one.
Calixarenes are able to accelerate reactions taking place inside the concavity by a combination of local concentration effect and polar stabilization of the
transition state. An extended resorcin  arene cavitandis found to accelerate the reaction rateof a Menshutkin reactionbetween quinuclidineand butylbromide by a factor of 1600  .
In heterocalixarenes the phenolic units are replaced by
heterocycles  , for instance by furans in calix [n] furanes and by pyridines in calix [n] pyridines. Calixarenes have been used as the macrocycleportion of a rotaxaneand two calixarene molecules covalently joined together by the lower rims form carcerands.
Building esthetic molecules with calixarenes include thus far a molecular
Football World Cup[http://www.rsc.org/publishing/journals/NJ/article.asp?doi=a805959d] .
*  a) cite book | author=Gutsche, C. David | title=Calixarenes | location=Cambridge | publisher=Royal Society of Chemistry | year=1989 | id=ISBN 0-85186-385-X; b) GoldBookRef | title=Calixarenes | file=C00783 | year=1995
*  cite journal | author=Antesberger J, Cave GW, Ferrarelli MC, Heaven MW, Raston CL, Atwood JL | title=Solvent-free, direct synthesis of supramolecular nano-capsules | journal=Chemical communications (Cambridge, England) | volume=. | issue=7 | year=2005 | pages=892–4 | pmid=15700072 | doi=10.1039/b412251h
*  cite journal | author=McMahon G, O’Malley S, Nolan K and Diamond D | title=Important Calixarene Derivatives – their Synthesis and Applications | journal=
Arkivoc| volume=Part | issue=vii | year=2003 | pages= [http://www.arkat-usa.org/ark/journal/2003/I07_McKervey/AM-720R/720R.asp Article]
*  cite journal | author=Nachtigall FF, Lazzarotto M and Braz FNJ | title=Interaction of Calix  arene and Aliphatic Amines: A Combined NMR, Spectrophotometric and Conductimetric Investigation | journal=Journal of the Brazilian Chemical Society | volume=13 | issue=3 | year=2002 | pages= | doi=10.1590/S0103-50532002000300002 [http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532002000300002 Article]
*  cite journal | author=Atwood JL, Barbour LJ, Jerga A | title=Organization of the interior of molecular capsules by hydrogen bonding | journal=
Proceedings of the National Academy of Sciences| volume=99 | issue=8 | year=2002 | pages=4837–41 | pmid=11943875 | doi=10.1073/pnas.082659799
*  cite journal | author=Thallapally PK, Lloyd GO, Atwood JL, Barbour LJ | title=Diffusion of water in a nonporous hydrophobic crystal | journal=Angewandte Chemie (International ed. in English) | volume=44 | issue=25 | year=2005 | pages=3848–51 | pmid=15892031 | doi=10.1002/anie.200500749
*  cite journal | author=Purse BW, Gissot A, Rebek J Jr | title=A deep cavitand provides a structured environment for the menschutkin reaction | journal=
Journal of the American Chemical Society| volume=127| issue=32 | year=2005 | pages=11222–3 | pmid=16089433 | doi=10.1021/ja052877
*  cite journal | author=Subodh Kumar, Dharam Paul, Harjit Singh| title=Syntheses, structures and interactions of heterocalixarenes | journal=
Arkivoc| volume=05-1699LU| issue= | year=2006 | pages=17–25 | pmid= [http://www.arkat-usa.org/ark/journal/2006/I09_General/1699/05-1699LU%20as%20published%20mainmanuscript.pdf Article]
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