Supramolecular chemistry molecular containers

Calixarenes, which are macrocyclic compounds, are one of the best building blocks to design molecular hosts in supramolecular chemistry [158]. Synthesis of calix[4]arenes, which have been adamantylated, has been reported [105, 109]. In calix[4]arenes, adamantane or its ester/carboxylic acid derivatives were introduced as substituents (Fig. 29). The purpose of this synthesis was to learn how to employ the flexible chemistry of adamantane in order to construct different kinds of molecular hosts. The X-ray structure analysis of p-(l-adamantyl)thiacalix[4]arene [109] demonstrated that it contained four CHCI3 molecules, one of which was located inside the host molecule cavity, and the host molecule assumed the cone-like conformational shape (Fig. 30). 

Since 1982 there have been enormous developments in metal-based chemistry, particularly the emergence of supramolecular chemistry - chemistry beyond the molecule, molecular architecture, and molecular engineering. Comprehensive Supramolecular Chemistry was published in 1996, a survey which contains much of interest to coordination chemists. Consequently in this volume review material relating to supramolecular systems is mainly restricted to developments since 1990. 

In supramolecular chemistry [31] iterative synthesis is frequently used for the construction of ribbon and belt shaped molecules [32]. The repeated Diels-Alder reaction is suitable for the preparation of beltenes, collarenes and cycla-cenes containing partially or fully unsaturated annelated six-membered rings. They are potential molecular receptors for appropriate substrates. Stoddart et al. synthesized the cyclacene 18 by Diels-Alder cyclization of the bisdiene 15 and the bisdienophil 16 [33] (Fig. 10). 

The study of the interactions between organic compounds and aUtali-metal cations, in the gas phase, is related to many topics such as ion solvation, catalysis and molecular recognition. Furthermore, mass spectrometry has been used for the analyses of organolithium compounds and supramolecular assemblies that contain lithium cations. Alkali cationization is an important ionization technique, implemented for the analyses of a wide range of organic compounds. Finally, gas-phase studies are also useful for the quantitative determination of lithium cation affinity. The interaction between lithium cation and organic substances is thus related to different aspects of gas-phase chemistry and mass spectrometry. 

By far, the greatest interest in 5-5 heterocyclic systems containing two heteroatoms in each ring has been in the field of supramolecular chemistry and in the preparation of molecular receptors of various types. One of the most widely used heterocyclic backbones for these receptors has been glycoluril 5 and its derivatives. 

The future targets of supramolecular photochemistry in CD chemistry will contain photoresponsive molecular machines, emission-based sensors, and energy transport systems. For construction of such systems, the design of three-dimen-sionally correct arrangement of component units will become important. The molecular modeling computation approach will be helpful for designing the systems and deeper understanding of structural features of chromophore-modified CDs and their complexes. 

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