Cucurbiturils are macrocyclic molecules consisting of glycoluril repeat units. These compounds are particularly interesting to chemists because they are molecular containers that are capable of binding other molecules within their cavity. The name is actually derived from the resemblance of this molecule with a pumpkin of the family of Cucurbitaceae. The cavity of cucurbit[6]uril has nanoscale dimensions with an approximate height of 50 nm, outer diameter 40 nm and inner diameter 20 nm^[1]. Cucurbiturils are synthesised from urea, glyoxal and formaldehyde. Cucurbiturils were first synthesized in 1905 by Behrend ^[2] but their structure was not elucidated until 1981 ^[3]. To date cucurbiturils composed of 5, 6, 7, 8, and 10 repeat units have all been isolated,³ which have internal cavity volumes of 82, 164, 279, 479, and 870 Å respectively. A cucurbituril composed of 9 repeat units has yet to be isolated. Other common molecular capsules that share a similar molecular shape with cucurbiturils include cyclodextrins and Calixarenes. Genera Abobra Acanthosicyos Actinostemma Alsomitra Ampelosycios Anacaona Apatzingania Apodanthera Bambekea Benincasa Biswarea Bolbostemma Brandegea Bryonia Calycophysum Cayaponia Cephalopentandra Ceratosanthes Chalema Cionosicyos Citrullus Coccinia Cogniauxia Corallocarpus Cremastopus Ctenolepis Cucumella Cucumeropsis Cucumis Cucurbita Cucurbitella Cyclanthera Dactyliandra Dendrosicyos Dicoelospermum Dieterlea Diplocyclos Doyerea Ecballium Echinocystis Echinopepon Edgaria Elateriopsis Eureiandra Fevillea Gerrardanthus Gomphogyne Gurania Guraniopsis... A nanometre (American spelling: nanometer) is 1. ... Urea is an organic compound of carbon, nitrogen, oxygen and hydrogen, with the formula CON2H4 or (NH2)2CO. Urea is also known as carbamide, especially in the recommended International Non-proprietary Names (rINN) in use in Europe. ... Glyoxal is an organic compound. ... The chemical compound formaldehyde (also known as methanal), is a gas with a strong pungent smell. ... Cyclodextrins are cyclic oligomers of glucose which typically contain 6-8 monomers in a ring. ... 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. ...

Cucurbituril is a popular rotaxane component. A rotaxane is a molecular structure consisting of a dumbbell shaped molecule that is threaded through a macrocycle or ring-like molecule. ...

Synthesis

Cucurbiturils are aminals and synthesized from urea 1 and glyoxal 2 via a nucleophilic addition to give the intermediate glycoluril 3. This intermediate is condensed with formaldehyde to give hexamer cucurbit[6]uril above 110 degrees celcius. Ordinarily multifunctional monomers such as 5 would undergo a step-growth polymerization that would give a distrubuation of products, but due to favorable strain and a abundance of hydrogen bonding the hexamer is the only reaction product isolated after precipitation.^[4] Image File history File links Cucurbituril. ... A hemiaminal is a functional group or type of chemical compound that has a hydroxyl group and a amine attached to the same carbon atom: -C(OH)(NR2)-. R can be hydrogen or an alkyl group. ... Urea is an organic compound of carbon, nitrogen, oxygen and hydrogen, with the formula CON2H4 or (NH2)2CO. Urea is also known as carbamide, especially in the recommended International Non-proprietary Names (rINN) in use in Europe. ... Glyoxal is an organic compound. ... In organic chemistry, a nucleophilic addition reaction is an addition reaction where in a chemical compound a pi bond is removed by the creation of two new covalent bonds by the addition of a nucleophile. ... A condensation reaction (also known as a dehydration reaction or dehydration synthesis when water is lost) is a chemical reaction in which two molecules or moieties react and become covalently bonded to one another by the concurrent loss of a small molecule, often water or methanol. ... Step-growth polymerization is a polymerization process that involves a chemical reaction between multifunctional monomer molecules. ... In chemistry a molecule experiences strain when in a chemical conformation there exist unfavorable bond angles or bond distances. ... Hydrogen bonds between water molecules are diagramatically represented by the black lines. ...

Decreasing the temperature of the reaction to between 75 and 90 degrees celcius can be used to access other sizes of cucurbiturils including CB[5], CB[7], CB[8], CB[9], and CB[10]. Although the other ring sizes are still formed in smaller percentages than CB[6]. The isolation of sizes other than CB[6] requires fractional crystallization and dissolution. CB[5], CB[6], CB[7], and CB[8] are all currently commercially available. The larger sizes are a particularly active area of research since they can bind larger and more interesting guest molecules thus expanding their potential applications.

Cucurbit[10]uryl is particularly difficult to isolate as it is obtained from the reaction mixture as a inclusion complex containing CB[5]. It has been isolated by introduction of a more strongly binding guest melamine that will displace the CB[5]. Free CB[10] is then obtained from by heating the C[10]- melamine complex with acetic anhydride.^[5] Melamine Melamine is a strong organic base with chemical formula C3H6N6, with the IUPAC name 1,3,5-triazine-2,4,6-triamine. ... Melamine Melamine is a strong organic base with chemical formula C3H6N6, with the IUPAC name 1,3,5-triazine-2,4,6-triamine. ... Acetic anhydride, also known as acetic acid anhydride, is the condensation product of two molecules of acetic acid. ...

Host guest chemistry

Cucurbiturils are efficient host molecules in molecular recognition and have a particularly high affinity for positively charged or cationic compounds. High association constants with positively charged molecules are attributed to the carbonyl groups that line each end of the cavity and can interact with cations is a similar fashion to crown ethers. The affinity of cucurbiturils can be very high. For example the affinity equilibrium constant of cururbit[7]uril with the positively charged 1-aminoadamantane hydrochloride is experimentally determined at 4.23*10¹². In chemistry, molecular recognition is a phenomenon in which molecules are distinguished accurately from other molecules. ... In chemistry, the equilibrium constant is a theoretically-calculated number associated to a reaction which is an useful tool to determine the concentration of various reactants or products in a system where chemical equilibrium occurs. ...

Host guest interactions also significantly influence solubility behavior of cucurbiturils. Cucurbit[6]uril dissolves poorly in just about any solvent but solubility is greatly improved in a solution of potassium hydroxide or in an acidic solution. The cavitand forms a positively charged inclusion compound with a potassium ion or a hydronium ion respectively which have much greater solubility that the uncomplexed neutral molecule^[6]. The chemical compound potassium hydroxide, (KOH) sometimes known as caustic potash, potassa, potash lye, and potassium hydrate, is a metallic base. ... An acid (from Arabic Azait meaning oil, often represented by the generic formula AH) is typically a water-soluble, sour-tasting chemical compound. ... In supramolecular chemistry host-guest chemistry describes Complexes that are composed of two or more molecules or ions held together in unique structural relationships by hydrogen bonding or by ion pairing or by Van der Waals force other than those of full covalent bonds. ... In host-guest chemistry an inclusion compound is a complex in which one chemical compound the host forms a cavity which molecules of a second compound the guest are located. ...

Applications

Given their high affinities to form inclusion complexes cucurbiturils have been employed as the macrocycles component of a rotaxane. After formation of the supramolecular assembly or threaded complex with a guest molecule such as hexamethylene diamine the two ends of the guest can be reacted with bulky groups that will then act as a stoppers preventing the two separate molecules from dissociating^[7]. A rotaxane is a molecular structure consisting of a dumbbell shaped molecule that is threaded through a macrocycle or ring-like molecule. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Hexamethylene diamine or 1,6-Hexanediamine is a organic compound with a hexamethylene hydrocarbon chain and two amine functional groups at either end. ...

Cucurbiturils host-guest properties have been explored for drug delivery vehicles. The potential of this application has been explored with cucurbit[7]uril that forms an inclusion compound with the important cancer fighting drugoxaliplatin. CB[7] was employed despite the fact that it is more difficult to isolate since it has much greater solubility in water and its larger cavity size can accommodate the drug molecule. The resulting complex was found to have increased stability and greater selectivity that may lead to less side effects^[8]. In host-guest chemistry an inclusion compound is a complex in which one chemical compound the host forms a cavity which molecules of a second compound the guest are located. ... Oxaliplatin - Wikipedia /**/ @import /w/skins-1. ...

Cucurbiturils have also been explored as supramolecular catalysts. Larger cucurbiturils, such as curcurbit[8]uril can bind multiple guest molecules. CB[8] forms a complex 2:1 (guest:host) with (E)-diaminostilbene dihydrochloride which is accommodated by CB[8]’s larger internal diameter of 8.8 angstrom and height 9.1 angstrom) ^[9]. The close proximity and optimal orientation of the guest molecules within the cavity enhances the rate of the photochemical cyclization to give cyclobutane dimer with a 19:1 stereoselectivity for the syn configuration when bound to CB[8]. In the absence of CB[8] the cyclization reaction does not occur, but only the isomerization of the trans isomer to the cis isomer is observed. ^[10]. An angstrom, angström, or Ã¥ngström (symbol Ã…) is a unit of length. ... An angstrom, angström, or Ã¥ngström (symbol Ã…) is a unit of length. ... Photochemistry is the study of the interaction of light and chemicals. ... Cyclobutane, C4H8, is a four carbon alkane in which all the carbon atoms are arranged cyclically, hence cyclobutane. ... Sucrose, or common table sugar, is composed of glucose and fructose. ... In chemistry, geometric isomerism is a form of stereoisomerism and describes the orientation of functional groups at the ends of a bond around which no rotation is possible. ... In chemistry, geometric isomerism is a form of stereoisomerism and describes the orientation of functional groups at the ends of a bond around which no rotation is possible. ...

CB[10] can is large enough to hold other molecular hosts such as a calixarene molecule. With a calixarene guest different chemical conformations (cone, 1,2-alternate, 1,3-alternate) are in rapid equilibrium. Allosteric control is provided when an adamantane molecule forces a cone conformation with a calixarene - adamantane inclusion complex within a CB[10] molecule. 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. ... In chemistry, a chemical conformation is the spatial arrangement of atoms in a molecule. ... In biochemistry, an enzyme or other protein is allosteric if its activity or efficiency changes in response to the binding of an effector molecule at a so-called allosteric site. ... Adamantane (Tricyclo[3. ...

Nomenclature

Cucurbiturils are commonly written as cucurbit[#]uril, where the number of repeat units is indicated within the brackets. A common abbreviation is CB[#] where again the number of repeat units is included within the brackets.

Related compounds

Inverted cucurbiturils or iCB[x] are CB analogues with one glycoluril repeating unit inverted ^[11]. In this unit the methine protons actually point inwards instead of outwards and this makes the cavity less spaceous. Inverted cucurbiturils form in the course of an ordinary CB forming reaction as a side-product with yields between 2 and 0.4%. Isolation of this type of CB compounds is possible because it is more difficult to form inclusion compounds that ordinarily form with regular CB's. Inverted cucurbiturils are believed to be the kinetically controlled reaction products because the addition of deuterated hydrochloric acid or DCl to iCB[6] results in a mixture of CB[5], CB[6] and CB[7]in a 24:13:1 ratio. In polymer chemistry, a structural unit is a building block of a polymer chain. ... -1... Thermodynamic reaction control or kinetic reaction control in a chemical reaction can decide the composition in a reaction product when competing reactions lead to different products under different reaction conditions. ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance of one atom in 6500 of hydrogen. ... The chemical substance hydrochloric acid is the aqueous (water-based) solution of hydrogen chloride (HCl) gas. ...

A cucurbituril cut in half along the equator is called a hemicucurbituril. A hemicucurbituril is a macrocycle composed of alternating units of methylene (CH2) and N-substituted ethylene urea units. ...

Systematic name

Cucurbit[6]uril goes by the systematic name of Dodecahydro-1H, 4H, 14H, 17H-2, 16:3, 15-dimethano-5H, 6H, 7H, 8H, 9H, 10H, 11H, 12H, 13H, 18H, 19H,20H, 21H, 22H, 23H, 24H, 25H, 26H-2, 3, 4a, 5a, 6a, 7a, 8a, 9a, 10a, 11a, 12a, 13a, 15, 16, 17a, 18a, 19a, 20a,21a, 22a, 23a, 24a, 25a, 26a-tetracosaazabispentaleno[1’’’, 6’’’:5’’, 6’’, 7’’]cycloocty[1’’, 2’’, 3’’:3’,4’]pentaleno(1’, 6’:5, 6, 7)-cycloocta(1, 2, 3-gh:1’, 2’, 3’-g’h’)cycloocta(1, 2, 3-cd:5, 6, 7-c’d’)dipentalene-1, 4,6, 8, 10, 12, 14, 17, 19, 21, 23, 25-dodecone.^[12] So lets stick to Cucurbituril.

References

1. ^  Review: The Cucurbit[n]uril Family Jason Lagona, Pritam Mukhopadhyay, Sriparna Chakrabarti, Lyle Isaacs Angewandte Chemie International Edition Volume 44, Issue 31, Pages 4844 - 4870 2005 Abstract
2. ^  Behrend et al Liebigs Ann. Chem. 1905, 339, 1.
3. ^  Cucurbituril W. A. Freeman, W. L. Mock, and N.-Y. Shih J. Am. Chem. Soc., 1981, 103, 7367. First Page
4. ^ Cucurbituril Homologues and Derivatives: New Opportunities in Supramolecular Chemistry Acc. Chem. Res., 36 (8), 621 -630, 2003. ref
5. ^  Cucurbit[10]uril J. Am. Chem. Soc., 127 (48), 16798 -16799, 2005. ref
6. ^  US patent 6365734 Patentstorm
7. ^  Mono-, Oligo- und Polyrotaxane mit Cucurbituril und gemischte Polyrotaxane mit Cucurbituril und alpha-Cyclodextrin mittels Selbstorganisation Claudia Meschke 1999 Online German language
8. ^  Novel molecular drug carrier: encapsulation of oxaliplatin in cucurbit[7]uril and its effects on stability and reactivity of the drug Young Jin Jeon, Soo-Young Kim, Young Ho Ko, Shigeru Sakamoto, Kentaro Yamaguchi and Kimoon Kim Organic & Biomolecular Chemistry, 2005, 3(11), 2122 - 2125 Abstract
9. ^  The complex formation of a,w-dicarboxylic acids and a,w-diols with cucurbituril and a-cyclodextrin. the first step to the formation of rotaxanes and polyrotaxenes of thepolyester type Hans-Jürgen Buschmann, Klaus Jansen, Eckhard Schollmeyer Acta Chim. Slov. 1999, 46(3), pp. 405-411 Article
10. ^  A facile, stereoselective [2 + 2] photoreaction mediated by cucurbit[8]uril Sang Yong Jon, Young Ho Ko, Sang Hyun Park, Hee-Joon Kim and Kimoon Kim Chemical Communications, 2001, (19), 1938 - 1939 DOI Abstract
11. ^  Template directed photodimerization of trans-1,2-bis(n-pyridyl)ethylenes and stilbazoles in water Mahesh Pattabiraman, Arunkumar Natarajan, Raja Kaliappan, Joel T. Mague and V. Ramamurthy Chemical Communications, 2005, (36), 4542 - 4544 DOI Abstract Full Article
12. ^  The Cucurbit[n]uril Family: Prime Components for Self-Sorting Systems Simin Liu, Christian Ruspic, Pritam Mukhopadhyay, Sriparna Chakrabarti, Peter Y. Zavalij, and Lyle Isaacs J. Am. Chem. Soc.; 2005; 127(45) pp 15959 - 15967; (Article) DOI: 10.1021/ja055013x Abstract cross-eyed stereoview More
13. ^  Cucurbit[10]uril Simin Liu, Peter Y. Zavalij, and Lyle Isaacs J. Am. Chem. Soc.; 2005; 127(48) pp 16798 - 16799; (Communication) DOI: 10.1021/ja056287n Abstract
14. ^  The Inverted Cucurbit[n]uril Family Isaacs, L.; Park, S.-K.; Liu, S.; Ko, Y. H.; Selvapalam, N.; Kim, Y.; Kim, H.; Zavalij, P. Y.; Kim, G.-H.; Lee, H.-S.; Kim, K. J. Am. Chem. Soc.; (Communication); 2005; 127(51); 18000-18001. DOI: 10.1021/ja056988k Abstract