Guests supramolecular complexes

Goshe, A.J., Steele, I.M., Ceccarelli, C., Rheingold, A.L. and Bosnich, B. (2002) Supramolecular chemistry and self-assembly special feature supramolecular recognition on the kinetic lability of thermodynamically stable host-guest association complexes. Proceedings of the... 

The Ag cations are coordinated to two sulfur atoms of different cavitands with Ag-S distances in the range 2.47-2.50 A. In the solid, efficient r-stack-ing of the P-phenyl groups with the picrate anions stabilizes the supramolecular complex (Fig. 10). The two cavitands are aligned along their common C4 axis and offset by about 45°, leading to a helical structure. The inner space is reduced by the occupancy of the sulfur atoms, and there is probably not enough room to accommodate small guests inside the cavity. 

This new type of supramolecular assembly opens the route to the design of more elaborated systems and for instance the propensity of the phosphorylated cavitand 12b to bind to poly-methylammonium guests, was further illustrated by the formation of the supramolecular complex depicted in Fig. 12. The fourfold symmetrical tetrapyridinium porphyrin [porphyry ll insoluble in chloroform was used as guest and was readily dissolved in chloroform solution in the presence of four equivalents of 12b [93]. 

We further addressed the use of the nucleic acids as biopolymers for the formation of supramolecular structures that enable the electronic or electrochemical detection of DNA. Specifically, we discussed the use of aptamer/low-molecular-weight molecules or aptamer/protein supramolecular complexes for the electrical analysis of the guest substrates in these complexes. Also, nucleic acid-NPs hybrid systems hold a great promise as sensing matrices for the electrical detection of DNA in composite three-dimensional assemblies. While sensitive and selective electrochemical sensors for DNA were fabricated, the integration of these sensor configurations in array formats (DNA chips) for the multiplexed analysis of many DNAs can also be envisaged. 

The examples given in Figure 1 illustrate not only the persisting problems to identify the structure of supramolecular complexes, but at the same time represent an interesting piece of history. The complex of a benzidino-cyclophane with a benzene guest molecule inside the macrocycle is likely the oldest published picture of such a supramolecular complex/31... 

Molecules incorporating interlocked [refs. 6, 7] components (Fig. 10.1) and their supramolecular analogs are suitable candidates for the generation of bistable chemical systems. A [2]pseudorotaxane is a supramolecular complex composed of a macrocyclic host encircling a linear guest. The two components are held together solely by noncovalent bonding interactions and they can... 

There is vast amount of literature involving studies of rare earth complexes with specific guests under the umbrella of supramolecular chemistry. The ligands involved in this area of rare earth complexes are not usually available commercially. In fact the ligands are designed and synthesized and later the rare earth complexes of the synthesized ligands are prepared. An example is cited here to illustrate the scheme involved in the preparation of lanthanide supramolecular complexes. 

The first host-guest supramolecular system of EMFs was obtained by the incorporation of Dy Cs2 into calix[8]arene (C8A), which was compared with the better known [Ceo-CSA] [162]. Perhaps attributable to the larger sizes and different conformational changes, it is more difficult for Dy Cs2 to form a complex with C8 A than Ceo, as evidenced by the longer reaction time and lower yield. However, once formed, [Dy Cs2-C8A] is much more stable than the Ceo analog. 

Recently, more efficient systems for the host-guest incorporation of EMFs were developed with azacrown ethers, which were able to form supramolecular complexes with La C82, with the accompanying electron transfer between them [76, 163]. Because the complexation is characteristic of EMEs, it was applied to the isolation of EMFs from the raw extracts thereby, exciting results were obtained (see also Section 1.2.33). 

Besides the above, the overall stability of a supramolecular complex will clearly also depend upon both the number and the nature of the available binding sites in each component. As discussed in Chapter 2, solvation effects may often also play an important role in determining the strength of host-guest binding. 

The Stoddart group has used the principles employed in their catenane studies to synthesise both a molecular trifoil knot and its isomeric large ring in very low yield. These isomers were separated by HPLC and characterised by liquid secondary ion mass spectrometry. The synthetic procedure, which is illustrated schematically in Figure 5.26, was based on the formation of a double-stranded supramolecular complex between an acyclic 7C-electron-rich, 1,5-dioxynaphthalene-based polyether and an acyclic 7i-electron-deficient bipyridinium-based tetracation. The extremely low efficiency of the synthesis in this case appears to reflect an unfavourable solution geometry of the intermediate host-guest complex - the latter... 

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