Supramolecular assemblies, importance control

Crystallization amounts by nature to the self-assembly of very large, boundaryless supramolecular species. Its control is a goal of major importance in order to be able to generate solid-state materials of specific structural and physical properties (see also Sections 7.1, 7.2, 9.4.4 [7.39-7.42, 9.105, 9.245]). Supramolecular effects play a crucial role. Directional growth of materials may be induced by a template and involve molecular recognition [9.246], occurring by epitaxy [9.247] or on oriented thin films [9.248]. 

At present, the known catenanes can be divided into two categories - those prepared by metal template synthesis and those synthesised in the absence of a metalion influence. A considerable number of catenanes of the first type have been prepared by Sauvage et al. as well as by a number of other workers. However, discussion on these important metal-ion-directed systems is deferred to the next chapter in which particular supramolecular assemblies produced by metal-ion-controlled procedures are discussed. 

The field of supramolecular chemistry is concerned with a large number of systems ranging from simple host-guest complexes to more complicated solution assemblies, as well as two-dimensional (organized monolayers) and three-dimensional assemblies (crystalline solids). Nonco-valent interactions play an important role in the kinetic assembly and thermodynamic stabilization of all these systems and constitute their most distinctive feature. Electron-transfer reactions can obviously be affected by supramolecular structures, but the reverse is also true. It is possible to alter the structure and the thermodynamic stability of supramolecular assemblies using electrochemical (redox) conversions. In other words, electron-transfer reactions can be utilized to exert some degree of control on supramolecular aggregates. Provided in this article is an overview of the interplay between supramolecular structure and electron-transfer reactions. 

Stemming from their multifarious roles in natural processes, [metallo] porphyrins have found numerous applications in artificial systems aimed at mimicking important biological functions. Many different metalloporphyrins have been designed in order to accomplish specific tasks and, in particular, novel approaches have been used to assemble several porphyrins into a cluster. This ability to concentrate metalloporphyrins into a supramolecular assembly is of special relevance in that it takes us one step closer to constructing practical devices. This chapter will attempt to review the progress made in the assembly of porphyrin derivatives into supramolecular systems and will describe the aptitude of such assemblies to photosensitize particular reactions. The work described here is primarily concerned with trying to reproduce, under controlled conditions, some of the important features of photosynthetic reaction center complexes. 

Control of molecular self-assembly to generate supramolecular architectures that are organized in well-defined geometries is important in various fields of science and technology [ 1,2], As porphyrins and phthalocyanines (Pcs) serve as components of molecular materials that possess imique electronic, magnetic and optical properties [3,4], supramolecular assembly based on them is subject to intense research targets. In this section the basic elements of supramolecules based on porphyrins are described and the creation of op-... 

In this chapter we describe the basic principles involved in the controlled production and modification of two-dimensional protein crystals. These are synthesized in nature as the outermost cell surface layer (S-layer) of prokaryotic organisms and have been successfully applied as basic building blocks in a biomolecular construction kit. Most importantly, the constituent subunits of the S-layer lattices have the capability to recrystallize into iso-porous closed monolayers in suspension, at liquid-surface interfaces, on lipid films, on liposomes, and on solid supports (e.g., silicon wafers, metals, and polymers). The self-assembled monomolecular lattices have been utilized for the immobilization of functional biomolecules in an ordered fashion and for their controlled confinement in defined areas of nanometer dimension. Thus, S-layers fulfill key requirements for the development of new supramolecular materials and enable the design of a broad spectrum of nanoscale devices, as required in molecular nanotechnology, nanobiotechnology, and biomimetics [1-3]. 

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