Ring structures supramolecular assemblies

Abstract In this chapter, recent progress in the synthesis, crystal structures and physical properties of monomeric phthalocyanines (Pcs) is summarized and analysed. The strategies for synthesis and modification of Pcs include axial coordination of central metal ions, peripheral substitution of Pc rings and the ionization of Pcs. The crystal structures of various typical Pcs, especially the effects of different synthetic and modification strategies on the supramolecular assemblies of Pcs via %—% interactions between Pc rings, are discussed in detail. Finally, the UV-vis spectroscopic, conducting, magnetic and catalytic properties of some Pcs with crystal structures are presented briefly, and the correlations between various properties and the molecular structure discussed. 

The stronger excitonic interaction in EB assemblies than that of ACR or AMAC is apparently due to a greater hydrophobic surface area of the former, as estimated from computer modeling studies (MacSpartan). Such increased hydrophobic surface is not expected from their structures (three six-membered ring systems) it also results in an enhanced entropic contribution to the binding energy when the probe is transferred from the aqueous phase to the interior of BAZrP, where there is little or no water. Therefore, the formation of these supramolecular assemblies may indeed involve a large entropic component, but this needs to be demonstrated experimentally. 

Hydrophobic forces are also important in the assemblies of metallo-supramolecular catenanes. One of the most interesting examples is formed when one of the unpolar bipyridine ligands of one macrocycle is included spontaneously in the other macrocycle s internal cavity [39]. Here, the benzene unit of the one macrocycle serves as a guest molecule for the other macrocycle, and the cyclization is favored by n-n interactions. In addition, the minimization of hydrophobic surfaces in polar medium constitutes the second driving force for the catenane formation. The quantitative formation of the [2]catenanes 31a and 31b based on this principle are depicted in Figure 13. Formation of catenane 31b was found to be reversible. Even at room temperature, two monomeric ring structures equilibrate quickly due to the labile nature of Pd-N bond and interlocked molecular ring system 31b is formed. 

Since the w-planes of the pyrrole unit also enable stacking, pyrrole rings can act as potential building blocks for nanoscale supramolecular structures. Thus, supramolecular assemblies built from planar pyrrole-based anion receptors would show anion-responsive sensing behavior in the forms of soft materials. In 2005, Maeda... 

Supramolecular structures such as rotaxanes occasionally play important roles in enzymatic activities. For example, DNA polymerases contain sliding clamps in which the ring-shaped protein assemblies form supramolecular complexes. The ring-shaped clamp peptides of DNA (or RNA) polymerases participate in binding two polynucleotide chains for replication. ° The clamps have no active sites and replication of polynucleotides is difficult without clamps. Similarly, cyclodextrins (CDs) and other host molecules are ring-shaped host molecules that include various guests to form supramolecular complexes such as rotaxanes. ... 

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