Topologically complex molecules

In this section we want to propose an alternative approach to analyzing the topological chirality of topologically complex molecules. When we speak of the topology of a molecule we are focussing on how the structure could be deformed. Of... 

It should be stressed that the coding for the formation of these topologically complex molecules needs to be carefully controlled in order to obtain the desired structures. To illustrate this, consider ligand 7.59, which contains two didentate metal-binding domains. This might be expected to react with octahedral metal ions to give a triple-helical dinuclear complex. Reaction with iron(n) does indeed give a species of stoichiometry [Fe2(7.59)3]4+ however, the crystal structure reveals that an untwisted complex, 7.60, has been formed. 

Self-assembly is a particular powerful tool in synthesising up large scale nanostructures are topologically complex molecules such as molecular machines and topologically interlocked species. 

Our intention in this chapter is to draw attention to the chiral aspects of self-assembled polynuclear complexes, and to show how the study of properties related to chirality can afford useful information. After a brief review of the nature of chiral centres in these complexes and the experimental methods used for studying them, we will discuss a number of structure types which are currently attracting interest, such as helicates, dendrimers, molecular boxes, and topologically complex molecules. 

Sauvage and Dietrich-Buchecker have developed a beautiful chemistry of topologically complex molecules in which complexation reactions are designed to favour the threading and interweaving necessary to produce the topological complexity [92], In... 

SUPRAMOLECULAR CHEMISTRY AIDING THE FORMATION OF TOPOLOGICALLY COMPLEX MOLECULES... 

It is clear from the drawings in Fig. I that pure chance is an inefficient way to make topologically complex molecules. While covalent-bonding strategies are valid, supramolecular chemistry has all but come into its own in the... 

By definition, topologically chiral molecules are those whose enantiomers cannot be interconverted by continuous deformation and therefore racemization is totally excluded as long as no bond in their organic backbone is broken. In addition, the combination of this latter topological property with the high thermodynamic stability of copper(I) 2,9-diphenylphenanthroline complexes provides us with potential catalysts for enantioselective processes. 

The principal idea of this present essay was to show how the unique preorganization of functional groups in self-assembled dimers of tetra-urea calix[4]arenes can be used to prepare novel multi-rotaxanes and -catenanes or topologically even more complex molecules and supramolecular structures. We will conclude by summarizing some related studies in which calixarenes were used in a different way as building blocks for the construction of such structures or assemblies. 

To our knowledge, topologically chiral molecules have not yet been resolved into enantiomers. However, we may anticipate that their energy barrier to racemization will be extremely high, compared to Euclidean chiral molecules. Therefore they are expected to be useful in enantioselective interactions or reactions. For example, it has been shown that tetrahedral copper(I) bis-2,9-diphenyl-l,10-phenanthroline complexes (which form the catenate subunits) are good reductants in the excited state [97] therefore the chiral Cu(I) catenates could be used for enantioselective electron-transfer reactions. Alternatively, the resolution of topologically chiral molecules would allow to answer fundamental questions, such as what are the chiroptical properties of molecular trefoil knots ... 

For more complex molecules, such as 1-propene, the interactions between topologically distant atoms must also be included. These contributions commonly involve van der Waals interactions and electrostatic interactions. Unlike the bonded interactions, the nonbonded interactions may have either positive... 

Bonchev, D. (1997). Novel Indices for the Topological Complexity of Molecules. SAR QSAR Environ.Res., 7, 23-43. 

Overall connectivity indices vere proposed as a meaningful measure of topological complexity of molecules, since they satisfy two fundamental requirements to a complexity measure to increase with both the number of structural elements and their intercoimectedness the basic idea is that The higher the connectivity of molecular graph and its connected subgraphs, the more complex the molecule [Bonchev and Trinajstic, 1977]. 

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