Macrocyclic molecules, supramolecular

Abstract Calix[n]arenes represent a well-known family of macrocyclic molecules with a broad range of potential applications in many branches of supramolecular chemistry. Because of their preorganisation, calix[n] arenes are frequently used as building blocks and molecular scaffolds in the construction of more elaborate systems, such as artificial enzyme biomimetics and receptors. This review is focused on the recent development of calixarene-based anion receptors. 

In contrast, supramolecular chemistry is directed towards the predictable formation of exactly defined structures, relying mostly on small molecules. Thus, the molar mass of a macrocyclic molecule is up to several orders of magnitude smaller... 

In this chapter, the recent progress in the understanding of the nature and dynamics of excess (solvated) electrons in molecular fluids composed of polar molecules with no electron affinity (EA), such as liquid water (hydrated electron, and aliphatic alcohols, is examined. Our group has recently reviewed the literature on solvated electron in liquefied ammonia and saturated hydrocarbons and we refer the reader to these publications for an introduction to the excess electron states in such liquids. We narrowed this review to bulk neat liquids and (to a much lesser degree) large water anion clusters in the gas phase that serve as useful reference systems for solvated electrons in the bulk. The excess electrons trapped by supramolecular structures (including single macrocycle molecules ), such as clusters of polar molecules and water pools of reverse micelles in nonpolar liquids and complexes of the electrons with cations in concentrated salt solutions, are examined elsewhere. 

Vibrational spectroscopy is an important complementary tool to x-ray diffraction for stmctural characterization of materials, including supramolecular compounds. Unlike x-ray diffraction, where all the data must be collected to give the stmcture of the molecule, vibrational spectroscopy can be used to zero-in on part of the structure of interest. Furthermore, information on guest—host interactions of inclusion compounds can be readily determined from infrared (IR) and Raman spectra, whereas this information is not readily accessible from x-ray diffraction. Therefore, IR spectroscopy and more recently Raman spectroscopy are used to study the stmcture and dynamics of inclusion compounds. IR spectroscopy is also widely and routinely used to characterize supramolecular compounds containing macrocyclic molecules. The stmc-tures and dynamics of these compounds can also be studied using resonance Raman spectroscopy. 

IR and Raman spectroscopies were used to study the structures of a wide range of supramolecular compounds containing macrocyclic molecules. Some examples of the use of vibrational spectroscopy in structural studies of these compounds will now be given. 

The pleated loop conformation was also found in the solid state structures of a monopotassium salt of C[8] reported by Fronun [94a] and obtained by its treatment with K2CO3 in a two-phase H2O/THF system. The macrocycles are supramolecularly stacked one over the other to give a one-dimensional system with an inner coaxial channel (Fig. 7.27). A 10-molecule water cluster with a distorted cubane core is sandwiched between two cmisecutive calixarenes [94a]. 

Fig. 8.1 Schematic presentation of strategies for the construction of hydrogen bonded organic nanotubes. Nanotubes from unimolecular, a helical, b tubular molecules, supramolecular, c bundles of rod-like molecules, d the stacking of macrocyclic molecules, and e aggregation of wedge-like molecules. The dotted red lines represent hydrogen bonding...

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). 

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