Inclusion compound

Example of an inclusion complex consisting of a p-xylylenediammonium bound within a cucurbituril[1]

In host-guest chemistry, an inclusion compound is a complex in which one chemical compound (the "host") forms a cavity in which molecules of a second "guest" compound are located. The definition of inclusion compounds is very broad, extending to channels formed between molecules in a crystal lattice in which guest molecules can fit. If the spaces in the host lattice are enclosed on all sides so that the guest species is ‘trapped’ as in a cage, the compound is known as a clathrate. In molecular encapsulation, a guest molecule is actually trapped inside another molecule.

Cyclodextrin inclusion compounds

Inclusion complexes are formed between cyclodextrins and different guest molecules such as ferrocene. When a solution of both compounds in a 2:1 ratio in water is under hydrothermal conditions at 100 degree C for 2 days and then allowed to rest for 10 hours at room temperature orange-yellow crystals form. X-ray diffraction analysis of these crystals reveals a 4:5 inclusion complex with 4 molecules of ferrocene included in the cavity of 4 cyclodextrine molecules and with the fifth ferrocene molecule sandwiched between two stacks of ferrocene – cyclodextrine dimers.

Cyclodextrin also forms inclusion compounds with fragrance molecules. As a result, the fragrance molecules have a reduced vapor pressure and are more stable towards exposure to light and air. When incorporated into textiles the fragrance lasts much longer due to the slow-release action.

References

  1. ↑ Freeman, Wade A. (1984). "Structures of the p-xylylenediammonium chloride and calcium hydrogensulfate adducts of the cavitand 'cucurbituril', C36H36N24O12". Acta Crystallogr B: 382–387. doi:10.1107/S0108768184002354.
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