Host design

In order lo design a host that will selectively bind a particular guest, we make use of the chelate and macrocyclic effects as well as the concept of complementarity (matching of host and guest steric and electronic requirements) and, crucially, host preorganisation. 

Overall, the thorough application of these very broad principles has been generalised into what has been referred to as complete coordination chemistry , encompassing both supramolecular and classical (Werner) inorganic coordination chemistry. 

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E. Weber, ed., Supramolecular Chemisty II—Host Design and Molecular Recognition, Top. Curr. Chem., Vol. 175, Springer, Bedin-Heidelberg, 1995. 

Nature of the Concept (Coordinatoclathrate Concept) and Basic Host Design... 

Thus, the Platonic and Archimedean solids not only provide a means for host design, but a way in which to maximize chemical information, allowing the chemist to simplify the structures of complex molecular frameworks and, in effect, engineer host-guest systems. 

The most difficult problem in the design of the enzyme model clearly lies in the difficulty of specific introduction of the functional groups into the host skeleton. For example, preparation of an enzyme model by use of fi-cyclodextrin often requires the introduction of two or more functional groups at certain positions among 7 primary (C6) and 14 secondary (C2 and C,) reactive positions. Unless one expects an accidental success by the use of any nonspecific functionalization, it is inevitably necessary for the host design to solve these problems. 

We now can prepare, in principle, enzyme models by use of the concept of host design, where artificial enzymes are so designed as multiple recognition hosts schematically shown in Fig. 20. Although unsubstituted cyclodextrins are well known to catalyze some organic reactions such as ester hydrolysis, their catalytic activities are relatively small. Recent progress in cyclodextrin chemistry has shown that it is possible to enhance the catalytic... 

Supramolecular Chemistry II Host Design and Molecular Recognition... 

Perhaps the most important concepts in supramolecular host design and preorganisation and complementarity, which encapsulate more traditional concepts such as the macrocyclic effect. 

By way of comparison, acyclic podand hosts analogous to compound 3.33 have been produced in order to assess the importance of the rigid preorganisation afforded by a cyclic host. Comparison of the closely related podand 3.36 (which is estimated to possess over 10 000 possible conformations, only two of which can bind cations in a convergent manner) and 3.33 (which is locked in only one conformation) shows that the spherand binds Li+ more than 1012 times more effectively. This highlights the importance of preorganisation effects in host design. 

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