Host-guest compounds, classification

Table 1.2 Classification of common host-guest compounds of neutral hosts.

Apart from the basic classification scheme given above, extremely varied structural types of supermolecules were developed, supplying a more detailed specification of supramolecular compounds by using trivial names. In the cases of the host-guest compounds, they normally refer to a particular feature of the host molecule. 

Fig. 2. Classification/nomenclature of host—guest type inclusion compounds, definitions and relations (/) coordinative interaction, (2) lattice barrier interaction, (J) monomolecular shielding interaction (I) coordination-type inclusion compound (inclusion complex), (II) lattice-type inclusion compound (multimolecular/extramolecular inclusion compound, clathrate), (III) cavitate-type inclusion compound (monomolecular/intramolecular inclusion...

For a new proposal for the classification and nomenclature of host-guest-type compounds see Weber, E Josel, H.-P. J. Inch Phenom. 1, 79 (1983)... 

Fig. 2 General classification/nomenclature and descriptive terminology of host-guest supramolecular inclusion compounds...

Over time, the term clathrate has become strongly intertwined with both Cram s host-guest concept and om increasing understanding of intermolecular forces within crystals. By 1962, Brown had established the fundamental topologies adopted by inclusion compounds, and a comprehensive classification of all host-guest stmctmal types was proposed in 1983. ° Introduction of the supramolecular synthon concept by Desiraju and more recent analysis of weak hydrogen bonds and other interactions have been of immeasurable value. 

Fig. 7.2 Classification of intercalation compounds (a) host of chains weakly bonded together (b) three-dimensional host with one-dimensional lattice of sites for guest ions (c) layered host (two-dimensional host and two-dimensional lattice of sites) (d) three-dimensional host with three-dimensional lattice of sites.

Complexation is one of several ways to favorably enhance the physicochemical properties of pharmaceutical compounds. It may loosely be defined as the reversible association of a substrate and ligand to form a new species. Although the classification of complexes is somewhat arbitrary, the differentiation is usually based on the types of interactions and species involved, e.g., metal complexes, molecular complexes, inclusion complexes, and ion-exchange compounds. Cyclodextrins (CDs) are classic examples of compounds that form inclusion complexes. These complexes are formed when a guest molecule is partially or fully included inside a host molecule e.g., CD with no covalent bonding. When inclusion complexes are formed, the physicochemical parameters of the guest molecule are disguised or altered and improvements in the molecule s solubility, stability, taste, safety, bioavailability, etc., are commonly seen. 

The examples mi t have illistrated that functional grou (e.g. OH, COOH, NH,), as they are a component of classical crystal inclusion compounds are usually used for construction, cross-linking, and stabilization of the host lattice (Fig. 6a), and are not used, as could have been, for direct binding of guest molecules, e.g. via coordination or H-bonding (Fig. 6b). To speak with a newly developed classification system on inclusion compounds (see Chapter 1 of Vol. 140), tho are true clathrates and i t coordinatoclathrates (cf. Fig. 6, for a more detailed sj fication see Fig. 15 in Chapter 1 of Vol. 140). As in the case of urea and thiourea, a rather stable, but nearly invariable host lattice with rigidly... 

A classification of methods for preparing polymer-layered inorganic solid compounds takes into account the main processes involved in the synthesis of the final hybrid material. The nature of both the 2D host solid and the guest polyma- determines the pathway applicable to obtain a particular nanocomposite and, in certain cases, is decisive in the behavior of the resulting material. In... 

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