Host-guest complexation relies on interactions of molecules through secondary chemical bonds. Such complexation can lead to formation of loose associations, as well as to that of very stable adducts. In formation of these addition compounds, important roles are played by hydrogen-bonding and hydrophobic interactions. In certain cases one of the reacting partners will wind up in a relatively enclosed space, embraced by the other reactant this is when the host-guest description is most appropriate. In general, any such interaction between host and guest is expected to change the properties of both molecules but it is the host molecule which. | Chapter 10 Host-guest chemistry in aqueous organometallic catalysis Cyclodextrins and the formation of inclusion compounds Host-guest complexation relies on interactions of molecules through secondary chemical bonds. Such complexation can lead to formation of loose associations as well as to that of very stable adducts. In formation of these addition compounds important roles are played by hydrogen-bonding and hydrophobic interactions. In certain cases one of the reacting partners will wind up in a relatively enclosed space embraced by the other reactant -this is when the host-guest description is most appropriate. In general any such interaction between host and guest is expected to change the properties of both molecules but it is the host molecule which is looked at with anticipation of its reactivity being changed in a favourable manner. Among the best known and most versatile hosts are the various cyclodextrins 1 2 of which a- 0- and y-cyclodextrins are the most available. These are cyclic oligosaccharides built up of six seven or eight glucopyranose units respectively. These compounds can be prepared by enzymatic hydrolysis of starch. The undoubtedly most important member of the cyclodextrin family is 0-cyclodextrin 0-CD which has become a cheap and easily available chemical suitable for large scale applications. Schemes and show the common representations of the cyclodextrin structure s emphasizing the topological difference between the polar outer surface and the hydrophobic inner face of the molecules. It is worth mentioning that while 0-cyclodextrin has a rather rigid structure due to internal hydrogen bonding a- and y-cyclodextrins are structurally more flexible. 279 280 Chapter 10 The most important property of cyclodextrins is in their ability to accommodate guest molecules within their cavity which has a volume of 262 Â3 per molecule or 157 mL per mol of 0-CD cavity diameter  . In aqueous solution this cavity is filled with .
