Supramolecular structure, molecular

Such specifics of interaction between dipoles of H O, cations and anions mostly determine the structure of water solution. The simplest idea of it is provided by the statistical theory of diluted solutions of strong electrolytes proposed by Peter Joseph Debye (1884-1966) and Erich Armand Hiickel (1896-1980) in 1923. Under this theory ions are treated as rigid non-polarizable spheres separated by a uniform medium with high value of the dielectric constant. At that, structure of the solution is function of distances dipoles H O and ions. Depending on it, it is customary to distinguish molecular and supramolecular structure. Molecular structure is determined by a direct effect of ions on the orientation and mobility of water dipoles and is manifested first of all by the formation of hydrates. Supramolecular structure is caused by undisturbed interaction of H O molecules between each other (Figure 1.2). 

Self-assembly refers to the molecules that form a class of clear and relatively stable structure by noncovalent interactions (such as hydrogen bonding, hydrophobic effects, etc.) and has some specific features of molecular aggregates or supramolecular structure. Molecular devices and machines and assemblies of molecular components designed to achieve a specific function continue to be a hot topic of research in the area of supramolecular chemistry. 

Macrocyclic receptors made up of two, four or six zinc porphyrins covalently connected have been used as hosts for di- and tetrapyridyl porphyrins, and the association constants are in the range 105-106 M-1, reflecting the cooperative multipoint interactions (84-86). These host-guest complexes have well-defined structures, like Lindsey s wheel and spoke architecture (70, Fig. 27a), and have been used to study energy and electron transfer between the chromophores. A similar host-guest complex (71, Fig. 27b) was reported by Slone and Hupp (87), but in this case the host was itself a supramolecular structure. Four 5,15-dipyridyl zinc porphyrins coordinated to four rhenium complexes form the walls of a macrocyclic molecular square. This host binds meso-tetrapyridyl and 5,15-dipyridyl porphyrins with association constants of 4 x 107 M-1 and 3 x 106 M-1 respectively. 

The series Structure and Bonding publishes critical reviews on topics of research concerned with chemical structure and bonding. The scope of the series spans the entire Periodic Table and addresses structure and bonding issues associated with all of the elements. It also focuses attention on new and developing areas of modem structural and theoretical chemistry such as nanostructures, molecular electronics, designed molecular solids, surfaces, metal clusters and supramolecular structures. Physical and spectroscopic techniques used to determine, examine and model structures fall within the purview of Structure and Bonding to the extent that the focus... 

Despite the vast number of reported syntheses, crystal structures, properties and applications of monomeric Pcs, it is still difficult to clarify clearly the synthetic mechanisms of Pcs in various conditions, to predict fully the supramolecular structures of Pcs in the solid state (except for a very few types of simple Pcs), and to elucidate completely the correlation between molecular structure and properties. The large-scale preparation and separation of some novel Pcs with interestingly properties is still very hard. On the basis of the great potential applications of Pcs in high-tech fields, exploitation of multi-functional Pc materials needs to be strengthened in the future. There is still plenty of room for further investigation of Pc chemistry. 

Molecular calculations provide approaches to supramolecular structure and to the dynamics of self-assembly by extending atomic-molecular physics. Alternatively, the tools of finite element analysis can be used to approach the simulation of self-assembled film properties. The voxel4 size in finite element analysis needs be small compared to significant variation in structure-property relationships for self-assembled structures, this implies use of voxels of nanometer dimensions. However, the continuum constitutive relationships utilized for macroscopic-system calculations will be difficult to extend at this scale because nanostructure properties are expected to differ from microstructural properties. In addition, in structures with a high density of boundaries (such as thin multilayer films), poorly understood boundary conditions may contribute to inaccuracies. 

Strong intermolecular interactions between active SCO mononuclear building blocks stem from the presence of efficient hydrogen-bonding networks or 7i-7i stacking interactions and have led to abrupt spin transitions [1], sometimes with associated hysteresis [2-4]. Despite the important efforts made by crystal engineers in establishing reliable connections between molecular and supramolecular structures on the basis of intermolecular interactions, the control of such forces is, however, difficult and becomes even more complicated when uncoordinated counter-ions and/or solvent molecules are present in the crystal lattice. 

Currently the main interest in template reactions lies in their key role in the controlled synthesis or the self-assembly of a variety of supramole-cular entities (449). One needs a combination of intuition, conjecture, and serendipity (450) a recent example of successfully combining serendipity and rational design is provided by the silver(I)-promoted assembly of one-dimensional stranded chains (451). One also needs an understanding of mechanism in order to optimize the selection and design of building blocks and templates for the generation of yet more sophisticated supramolecular structures references cited in this present review contain at least some kinetic or mechanistic information or speculation. Template routes to interlocked molecular structures have been reviewed (452), while a discussion of switching by transition metal contains a little about the kinetics and mechanisms of this aspect of template... 

A series of aggregation structures of bilayer forming azobenzene amphiphiles, CnAzoCmN+Br, both in single crystals and cast films was determined by the X-ray diffraction method and uv-visible absorption spectroscopy. From the relationship between chemical structures and their two-dimensional supramolecular structure, factors determining the molecular orientation in bilayer structure were discussed. Some unique properties based on two-dimensional molecular ordering were also discussed. 

Figure 9.1 shows some examples of a possible texture (supramolecular structure) variety for PSs of identical molecular composition and structure. All of these materials represent Si02 phase... 

Model of a supramolecular structure of polymolecular ensembles or clusters, determined by interaction and mutual arrangement of the forming molecules. At this level, the specific mechanisms of supramolecular chemistry, including molecular recognition, self-assembly, etc. [4] can be allocated. In most cases, it is possible to limit this area to objects with the sizes under 1 to 2 nm, since further increase in the sizes admits application of statistical concepts like phase and interphase surface. 

Thus, several processes may take place within supramolecular systems modulated by the arrangement of the components. These processes involve a modification of the physical and chemical processes of excited states when photoactive components are included in a supramolecular structure. Light excitation of a specific photoactive molecular subunit may also modify the electronic interactions between this subunit and other components, resulting in such phenomena as ... 

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