Host-guest molecular systems Subject

Since the pioneering work of Pedersen (1), Lehn (2), and Cram (3) on synthetic macrocyclic and macropolycyclic host systems such as the crown ethers, cryptands, and spherands, there has been an enormous development of the field of host-guest or supramolecular chemistry. Molecular hosts designed to bind inorganic and organic, charged and neutral guest species via cumulative, noncovalent interactions have all been reported and extensive reviews on this subject have appeared (4-8). 

To end this overview, let me say a few words about the likely evolution of the calculations devoted to theoretically analyze the stability and reactivity of cyclodextrin complexes. Hybrid methods have recently opened the door for the most sophisticated ab initio and DFT methods to deal with molecular systems with hundreds or even thousands of atoms if the reactive center is well localized within a particular zone of the whole macromolecular system. As computers keep on growing in capacity and theoretical methods are progressively more well established, theoretical work on host guest complexes will be ready to make a jump from the qualitative predictions, already available now, to the quantitative results. This will provide a powerful tool for the experiments as theory will be helpful not just to explain reactions already known but to predict new reactions and effects of the supramolecular environment that have been until now out of reach of precise measurements (as intermolecular forces are quite tenuous, their theoretical evaluation is subject to noticeable relative errors). On the other hand, it is to be noted that electronic calculations alone are not able to disclose the rich molecular dynamics of such a large molecular systems. Up to now MC and MD procedures have been restricted to find the more stable conformations but they are able to tell us more details about the mechanism of the inclusion process and reactivity inside CD and other large guests. The applicability of these methods to such problems has also been... 

In this chapter, we will concentrate on the subjects of synthetic strategies for (1) porphyrins and the capability of the products for molecular recognition of small organic substrates via intermolecular and noncovalent interactions (2) effective electron-transfer reaction regulated by intermolecular interaction " and (3) self-assembled porphyrin to construct supramolecular system for the guest. The Structures of porphyrins and their metalloporphyrin derivatives have attracted chemists due to their suitability as a host framework for organic guest molecules. 

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