Supramolecular dynamics

Metalloreceptors, and the supermolecules that they form, thus open up a vast area for the study of interactions and reactions between simultaneously co-bound organic and inorganic species [4.67,4.68]. In view of the number of metal-ion complexes known and of the various potential molecular substrates, numerous types of metalloreceptors may be imagined that would be of interest as abiotic chemical species or as bioinorganic model systems. 

The medium may have a marked effect on the shape of receptor molecules itself. Shape modifications could strongly influence their substrate binding properties, for instance in the case of amphiphilic cyclophane receptors subjected to hydrophobic-hydrophilic factors in aqueous solution. Such medium effects in action are visualized by the solid state structures of two different forms of the water-soluble hexasodium salt of the macrobicyclic cyclophane 66, which could be crystallized in two very different shapes an inflated cage structure 71 building up cylinders disposed in a hexagonal array and a flattened structure 72 stacked in molecular layers separated by aqueous layers in a lamellar arrangement [4.73]. These two 

The dynamic character of the p, a pair in the diammonium cryptates 52 represents the extent of dynamic fit. Thus, complementarity in the supermolecular species expresses itself in both steric and dynamic fit, strong or weak motional coupling between p and a depending on the degree of complementarity. 

Dynamic features of supermolecules correspond on the intermolecular level to the internal conformational motions present in molecules themselves and define molecular recognition processes by their dynamics in addition to their structural aspects. They add a further important facet to the behaviour of these species and may influence their functional features in reactions and transport processes as well as in polymolecular assemblies. 

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Cazacu, A., Pasc-Banu, A. and Barboiu, M. (2006) Molecular and supramolecular dynamics — a versatile tool for self organization of polymeric membranes systems. Macromolecular Symposia, 245—246, 435—438. 

Hybrid supramolecular dynamic membranes as selective information transfer devices. Desalination, 199, 521-522. 

We chose to show the application of techniques employed to study supramolecular dynamics to host systems that have defined binding sites and, therefore, form host-guest complexes with defined stoichiometries. CDs were chosen because they represent a host with only one binding site, and therefore can be viewed as a model system for hosts with the lowest degree of complexity. DNA was chosen because it provides multiple binding sites for small molecules, i.e. intercalative and groove binding, while the DNA is structurally fairly well defined. 

Fig. 1 Time ranges accessible to techniques commonly used to study supramolecular dynamics.

Fig. 6 Correlation curve showing the various processes that occur in different time regimes. Supramolecular dynamics can be measured in any of the time regimes between the antibunching and diffusion phenomena.

The application of the techniques discussed above to the binding of guests to DNA or cyclodextrins (CDs) is described below. The intent of this section is not to provide an exhaustive review and analysis of the available data, but the objective is to use examples to show how the different techniques were employed in studies of supramolecular dynamics. The values for rate and equilibrium constants stated below... 

This monograph described the techniques that can be used for the study of fast processes in supramolecular dynamics. Some of the techniques have been widely used while others have only been applied recently. Many of the techniques rely on the presence of a chromophore in the guest or host that can be used to monitor changes in absorption or fluorescence as the reaction proceeds. This feature is a reflection of the ease in building detection systems for absorption and fluorescence measurements, and in the case of fluorescence it is also related to the high sensitivity of this method. For systems that do not contain a chromophore the dynamics can be... 

CB thanks the Natural Sciences and Engineering Research Council of Canada (NSERC) for support of her research program in supramolecular dynamics in the form of operating and equipment grants, and TCSP thanks NSERC for a Canada Graduate Scholarship. 

Supramolecular dynamics, techniques for fluorescence correlation spectroscopy, 178-181... 

Fig. 4 Expression/amplification of the optimal constituent from a triple dynamic library of potential receptor molecules through induced fit interaction with a substrate molecule (abarbiturate). In addition, there is a non-covalent/supramolecular dynamic process involving substrate binding and exchange...

One may define molecular and supramolecular dynamic materials as materials whose components are linked through reversible covalent or non-covalent connections and undergo spontaneous and continuous change in constitution by assembly/disassembly processes in a given set of conditions. Such materials may in principle respond to multiple physical or chemical stimuli by constitutional variation and thus act as adaptive materials. 

Cazacu A, Michau M, Arnal-Herault C, Pasc-Banu A, Meffre A, Caraballo R, Pasc A, Barboiu M. Hybrid supramolecular dynamic membranes as selective information transfer devices. Desalination 2006 199 521-522. 

A1 Soufi, W., Reija, B., Novo, M., Felekyan, S., Kuehnemuth, R., Seidel, C. A. M., Fluorescence Correlation Spectroscopy, a Tool to Investigate Supramolecular Dynamics Inclusion Complexes of Pyronines with Cyclodextrin, J. Am. Chem. Soc. 2005, 127, 8775 8784. 

Another area of supramolecular dynamics pertains to the racemization of chiral assembhes. There are numerous examples of chiral self-assembled coordination structures in which chirahty is exhibited not only on the molecular level, but also on the supramolecular level. For example, helicates are inherently chiral even when assembled from achiral components. The P and M configurations of helicates are exclusively the properties of the supramolecular ensemble. 

Kawase T, Eujiwara N, Tsutumi M, Oda M, Maeda Y, Wakahara T, Akasaka T (2004) Supramolecular dynamics of cyclic [6]paraphenyleneacetylene complexes with [60]- and... 

Kawase T, Tanaka K, Seirai Y, Shiono N, Oda M (2003) Complexation of carbon nanorings with fullerenes supramolecular dynamics and structural tuning for a fullerene sensor. Angew Chem Int Ed 42(45) 5597-5600... 

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