Supramolecular substituents

Scheme 31 Supramolecular substituents In adenine—thymine and guanine—cytosine pairs. Reproduced from (2006MI) with kind permission from Springer Science and Business Media.

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). 

Dendrimers are taking their space in the tool box of the modern synthetic chemist. Dendritization might offer solutions to problems yet unsolved. Dendritic wedges, i. e. dendryl substituents of well-chosen size and generation allow us to tune molecular properties like solubility, steric accessability of reactive sites, redox behaviour, and other features. Easy-to-make dendrimers and dendrons will thus become extremely helpful for any chemist in the covalent as well as in the supramolecular world . 

It is interesting to note that even though the nature of the peripheral substituents on 158 and 160 are different, the complexation of zinc has little effect on the supramolecular stacked arrangement of the pz components. 

When radicals with bulky substituents are found within the internal channels of the zeolite, their interactions may be inhibited by the narrow diameter of the channels, allowing them to persist for a long time (shown by electron spin resonance (ESR) spectroscopy). These steric constraints are known as a supramolecular steric effect. 

Wilcox[102-104] A/,A/ -disubstitued (thio)urea derivatives studies on substituent effects in anion recognition and supramolecular chemistry... 

Keywords Crown compounds Liquid crystals Mesophases Metallomesogens Polymers Salt effects Self-assembly Substituent effects Supramolecular chemistry Phthalocyanines Cyclophanes... 

Terminal crown ethers with taper-shaped substituents often possess columnar phases. Sometimes, the columnar order is only observed after the complexation of specific salts. The uptake of salts often results in the crown ethers assembling side by side forming supramolecular cylinders with the crown moieties on the inside and the alkyl chains on the outside leading to possible ion-conducting arrangements within an insulating jacket. Indeed, it was shown that matrix-fixed tubular arrangements are ion conductors. 

A guest in a supramolecular bucket may participate in electron transfer with substituents at the rim of the bucket. Weidner and Pikramenou have studied di-... 

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