Inclusion complexation, encapsulation interaction and inclusion number in cyclodextrin chemistry

In this paper, the inclusion complexation between host and guest in cyclodextrin (CD) chemistry is carefully compared with the coordination interaction between central ion (Mx+) and ligands in coordination chemistry. In view of the importance of the concept of the coordination number (CN) of Mx+ in coordination compounds, the inclusion number (IN) is first defined to evaluate the nature of inclusion complexation between host and guest in CD supramolecular inclusion complexes. The similarities and differences between CN and IN are also discussed. The changes of the number and forms of water molecules both in CD hydrates and in CD crystal inclusion complex hydrates are reviewed. Moreover, this paper emphasizes the distinction between the two forms of CD-guest inclusion phenomenon, i.e., inclusion complexation and encapsulation interaction. Furthermore, the present work indicates that though chemical stoichiometric ratio can be used to characterize the inclusion phenomena, IN can better reveal the essence of inclusion phenomena in cyclodextrin chemistry.