Supramolecular definition

Intermolecular recognition and self-assembly processes both in the solid, liquid, and gas phases are the result of the balanced action of steric and electronic factors related to shape complementarity, size compatibility, and specific anisotropic interactions. Rather than pursuing specific and definitive rules for recognition and self-assembly processes, we will afford some heuristic principles that can be used as guidelines in XB-based supramolecular chemistry. 

Paraphrasing Corey s historic definition of synthon [203], Desiraju defined a supramolecular synthon as a structural unit within a supermolecule that can be formed or assembled by known or conceivable synthetic operations involving intermolecular interactions [204], The robustness of the XB has allowed several supramolecular synthons based on this interaction to be identified and some examples have been presented in this chapter. 

Within this approach, clathrates (for a definition see Chapter 1 in Vol. 140 of this series) and related lattice-type aggregates may be considered as multi-supramolecular systems where guest molecules are included in a crystal matrix. They allow a great many applications which have been specified in Vol. 140, first of all the separation of enantiomers by enantioselective recognition and inclusion of racemic guest molecules. 

As in the molecular case (Dl), the definition (D2) allows the supramolecular unit(s) to be determined by an operational NBO search of a given electron distribution ir(fi, r2,..., Fjv ) 12. Given the NBO molecular units of the distribution, we can search the intermolecular interactions (e.g., the table of perturbative donor-acceptor stabilizations) to determine the connecting noncovalent bonds that satisfy the required thermal threshold, and thereby determine the contiguously bonded supramolecular unit(s) by (D2). 

The examples cited in this chapter are but a rather small and arbitrary selection from the richly varied possibilities for supramolecular bonding. Recognition of the intrinsic chemical (partially covalent, exchange-type) character of supramolecular interactions leads inevitably to an extended definition of chemistry that includes many aspects of nanoscale aggregation, structure, and function in the biophysical and material-science domains. From this viewpoint, the molecule is seen to be... 

For many chemists LCs are mysterious and complex materials, their very definition defying a simple understanding. The basic idea behind this discussion of stereochemistry in LCs is that molecules and LCs represent the same phenomenon. Liquid crystals are supermolecules in a different way than are supramolecular assemblies. Indeed, LCs can be composed of supramolecular... 

FIGURE 5.11 Supramolecular, helical architecture and definition of pitch length p of chiral nematic liquid crystals. 

It was also noted by Farrington and co-workers that the chemical nature of the end-groups may have a substantial effect on the viscosity of bulk dendrimers, even under iso-free volume conditions [49]. This seems consistent with the establishment of interdendrimer interactions and supramolecular organization at rest in the bulk state. However, as in most other areas of dendrimer rheology, more data are desirable before definite conclusions can be drawn. 

In its simplest terms, let us consider a model supramolecular system as being a dyad (composed of two components or subunits) A B. From the point of view of a basic definition of supramolecular photochemistry, we may regard this system as being supramolecular if photon absorption by the system results in an electronically-excited state where the excitation is localised on a specific component. Likewise, if light absorption leads to electron transfer between the components such that the positive and negative charge are localised on specific components then the system is considered to be supramolecular. 

Computational modeling can be a very powerful tool to understand the structure and dynamics of complex supramolecular assemblies in biological systems. We need to sharpen the definition of the term model somewhat, designating a procedure that allows us to quantitatively predict the physical properties of the system. In that sense, the simple geometrical illustrations in Fig. 1 only qualify if by some means experimentally accessible parameters can be calculated. As an example, a quantitative treatment of DNA bending in the solenoid model would only be possible if beyond the mechanical and charge properties of... 

Pyridinedicarboxylie acid (dipicolinic acid) is definitely an excellent building block in coordination and supramolecular chemistry as outlined above. 

As Figure 3 illustrates, redox active guests introduce PET processes almost by definition and luminescent on-off switching is the norm. However, the inhibitions outlined in Section 5 have not prevented the designers of switchable luminescent devices from exploring systems which bind redox active guests. The combined forces of inorganic coordination chemistry and supramolecular science have proved to be too attractive in many of these instances. It is to be hoped that some of this effort will filter across to the examination of more on-off systems like 17 and 18. 

Science is a complicated matter and any definition of a research area is an oversimplification. This is especially true for a new domain in statu nascendi such as supramolecular chemistry [9]. However, a recent development in... 

Definitions have a clear, precise core but often fuzzy borders, where interpenetration between areas takes place. These fuzzy regions in fact play a positive role since it is often there that mutual fertilization between areas may occur. This is certainly also true for the case at hand, the case of supramolecular chemistry and its language [1.20]. 

Molecular and supramolecular devices are by definition formed from covalently and non-covalently linked components, respectively. One might envisage that covalently built devices made up of distinct but interacting components, retaining at least in part their identity as if they were bound together in a non-covalent fashion, could also belong to the supramolecular domain. Such a case has been argued for supramolecular photochemistry [A. 10] and could be extended to other supramolecular functions. 

This may be perceived as a significant stretching of the basic definition of supramolecular species. This definition is essential to charactere the identity of the field. 

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