Inclusion compounds classification

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...

Over the years the original strict sense of the term clathrate has become softened up since it was not always used correctly (see ref. 12, pp. 13). The immense increase of new host molecular structures starting off with the discovery of crown compounds in the middle of the sixties has made the situation more difficult The conventional classification system of inclusion compounds proved to be no longer suitable, because the new compounds can not be conveniently fitted into the existing terminology... 

For an early attempt to develop a new classification system for inclusion compounds, see Baron, M. Physical Methods in Chemical Analysis, Berl, W. (ed.). New York, Academic Press 1961, pp. 259... 

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

Carbohydrates, Recognition of, p. 169 Carbonic Anhydrase Models, p. 178 Carcerands and Hernicarcerands. p. 189 Cation-n Interactions, p. 214 Cavitands, p. 219 Chiral Guest Recognition, p. 236 Classical Descriptions of Inclusion Compounds, p. 253 Classification and Nomenclature of Supramolecular Compounds, p. 261 Clathrate Hydrates, p. 274 Conzplexation of Fullerenes, p. 302 Concepts in Ciystal Engineering, p. 319 Crown Ethers, p. 326 Cryptands, p. 334 Cryptophanes, p. 340 Cyclodextrins, p. 398... 

Classical Descriptions of Inclusion Compounds, p. 253 Classification and Nomenclature of Supramolecular Compounds, p. 261 Clathrate Hydrates, p. 274 Concepts in Crystal Engineering, p. 519 Crystal Structure Prediction, p. 371 Cyclodextrins, p. 398... 

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... 

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. 

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. 

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