Cage-type inclusion compounds

Clathrates (cage or inclusion compounds) are compounds that consist of a lattice of one type of molecule (a host molecule) trapping another type of molecule (a guest molecule) by intermolecular interactions. A clathrate is therefore a mechanical structure without chemical bonds. Such compounds include protein complexes containing -carotene or lipids (fatty acids) bound in the starch macromolecules (see Section 4.5.1.1). In some technological processes, such as extrusion, part of the free lipids is bound in this way. 

Packing of the cyclodexthn molecules (a, P, P) within the crystal lattice of iaclusion compounds (58,59) occurs in one of two modes, described as cage and channel stmctures (Fig. 7). In channel-type inclusions, cyclodextrin molecules are stacked on top of one another like coins in a roU producing endless channels in which guest molecules are embedded (Fig. 7a). In crystal stmctures of the cage type, the cavity of one cyclodextrin molecule is blocked off on both sides by neighboring cyclodextrin molecules packed crosswise in herringbone fashion (Fig. 7b), or in a motif reminiscent of bricks in a wall (Fig. 7c). 

Fig. 7. Schemes of crystalline cyclodextrin inclusion compounds (a) channel type (b) cage herringbone type (c) cage brick type (58).

Figure 7. Schematic representation of the packing arrangement in cyclodextrin complexes (a) channel type, (b) cage or herringbone type, and (c) brick type. (Reproduced with permission from W. Sanger in Inclusion Compounds, Vol. 2, J. L. Atwood, J. E. D. Davies, and D. D. MacNicol, Eds., Academic Press, New York, 1984, p. 231.)...

Figure 8. A stereoscopic view of the packing in the inclusion compound of 1,1,6,6-tetraphenylhexa-2,4-dyne-1,6-diol, 2, with (a) chalcone and (b) 9-anthraldehyde. 9-Anthraldehyde gives cage-type and chalcone gives channel-type structures. [Reproduced with permission from F. Toda, Topics Curr. Chem. 140, 43 (1987).]...

There are many other types of inclusion compounds of undefined stoichiometry in which the guest molecules are confined in tunnels and cages... 

Clathrates are crystalline inclusion compounds formed by the physical reaction between host molecules and low molecular weight gases as guests. In the clathrate structure there are two different types of cages which can entrap guest molecules into the network of host molecules. The three-dimensional clathrate structures can be determined by X-ray diffraction method. 

Still another type of topological isomerism is molecule in a cage . Formally, here belong the inclusion compounds... 

Inclusion compounds are crystalline hosts that have channels in which a guest molecule may reside, e.g., templated urea. Non-stoichiometric ICs are typically formed. Clathrates, or cage compounds, are a special type of inclusion compound that possess fully enclosed voids. Integral stoichiometries for their ICs are expected. For example, hydroquinone (1) forms a hydrogen-bonded trimer that can confine a... 

The sole cage-type complex 1.8 has almost the largest u/a ratio (5 1) in the present series of inclusion compounds except 2.23 (6 1) and 2.24 (11 2), but clearly the guest species in the latter cases are larger and the incorporated anionic moieties are smaller than that in the first one. 

Clathrates may be classified according to the shape of the cavity into the following types cryptatoclathrates the compounds of this type have cage structures (icpuTixov is secrecy in Creek) tubulatoclathrates—one-dimensional channel inclusion compounds (tubus is the Latin tube) ... 

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