Cavitand

{{short description|Molecule able to contain another molecule within itself}}

Image:Cucurbit-6-uril ActaCrystallB-Stru 1984 382.jpg bound with a guest p-xylylenediammonium{{cite journal |last= Freeman |first= Wade A. |journal= Acta Crystallographica Section B|year= 1984 |pages= 382–387 |title= Structures of the p-xylylenediammonium chloride and calcium hydrogensulfate adducts of the cavitand 'cucurbituril', C₃₆H₃₆N₂₄O₁₂ |doi= 10.1107/S0108768184002354 |volume=40|issue= 4 |bibcode= 1984AcCrB..40..382F |url= http://journals.iucr.org/b/issues/1984/04/00/a23241/a23241.pdf }}]]

In chemistry, a cavitand is a container-shaped molecule.{{cite journal | author = D. J. Cram | title = Cavitands: organic hosts with enforced cavities | year = 1983 | journal = Science | volume = 219 | issue = 4589 | pages = 1177–1183 | doi = 10.1126/science.219.4589.1177 | pmid = 17771285 | bibcode = 1983Sci...219.1177C | s2cid = 35255322 }} The cavity of the cavitand allows it to engage in host–guest chemistry with guest molecules of a complementary shape and size. The original definition proposed by Cram includes many classes of molecules: cyclodextrins, calixarenes, pillararenes and cucurbiturils.{{cite journal |last1=Moran |first1=John R. |last2=Karbach |first2=Stefan |last3=Cram |first3=Donald J. |title=Cavitands: synthetic molecular vessels |journal=Journal of the American Chemical Society |date=October 1982 |volume=104 |issue=21 |pages=5826–5828 |doi=10.1021/ja00385a064|bibcode=1982JAChS.104.5826M }} However, modern usage in the field of supramolecular chemistry specifically refers to cavitands formed on a resorcinarene scaffold by bridging adjacent phenolic units.{{cite book |last1=Jordan |first1=J. H. |last2=Gibb |first2=B. C. |editor1-last=Atwood |editor1-first=Jerry |title=Comprehensive Supramolecular Chemistry II |date=2017 |publisher=Elsevier |isbn=9780128031995 |pages=387–404 |chapter-url=https://www.sciencedirect.com/science/article/pii/B9780124095472107899 |chapter=1.16 - Water-Soluble Cavitands☆}} The simplest bridging unit is methylene ({{chem2|\sCH2\s}}), although dimethylene ({{chem2|\s(CH2)2\s}}), trimethylene ({{chem2|\s(CH2)3\s}}), benzal, xylyl, pyridyl, 2,3-disubstituted-quinoxaline, o-dinitrobenzyl, dialkylsilylene, and phosphonates are known. Cavitands that have an extended aromatic bridging unit, or an extended cavity containing 3 rows of aromatic rings are referred to as deep-cavity cavitands and have broad applications in host-guest chemistry.{{cite book |last1=Wishard |first1=A. |last2=Gibb |first2=B.C. |title=Calixarenes and beyond |publisher=Springer |isbn=978-3-319-31867-7 |pages=195–234 |chapter=A chronology of cavitands|doi=10.1007/978-3-319-31867-7_9 |year=2016 }}{{cite book |last1=Cai |first1=X. |last2=Gibb |first2=B. C. |editor1-last=Atwood |editor1-first=Jerry |title=Comprehensive Supramolecular Chemistry II |date=2017 |publisher=Elsevier |isbn=9780128031995 |pages=75–82 |chapter-url=https://www.sciencedirect.com/science/article/pii/B978012409547212582X |chapter=6.04 - Deep-Cavity Cavitands in Self-Assembly}} These types of cavitands were extensively investigated by Rebek, and Gibb, among others.