Self supramolecular

Fig. 31. Supramolecular (hydrogen-bonded) motifs of self-complementary molecules (196).

A particular point of interest included in these hehcal complexes concerns the chirality. The heUcates obtained from the achiral strands are a racemic mixture of left- and right-handed double heUces (Fig. 34) (202). This special mode of recognition where homochiral supramolecular entities, as a consequence of homochiral self-recognition, result from racemic components is known as optical self-resolution (203). It appears in certain cases from racemic solutions or melts (spontaneous resolution) and is often quoted as one of the possible sources of optical resolution in the biological world. On the other hand, the more commonly found process of heterochiral self-recognition gives rise to a racemic supramolecular assembly of enantio pairs (204). 

The following sections contain a review of many of the varied synthetic systems that have been developed to date utilising noncovalent interactions to form assembhes of molecules. These sections are loosely demarcated according to the most important type of noncovalent interactions utilized in conferring supramolecular order (ie, van der Waal s interactions, electrostatic interactions, and hydrogen bonds). For extensive reviews, see References 1,2,4—6,22,46,49,110—112. Finally, the development of self-assembling, self-replicating synthetic systems is noted. 

A second class of monolayers based on van der Waal s interactions within the monolayer and chemisorption (in contrast with physisorption in the case of LB films) on a soHd substrate are self-assembled monolayers (SAMs). SAMs are well-ordered layers, one molecule thick, that form spontaneously by the reaction of molecules, typically substituted-alkyl chains, with the surface of soHd materials (193—195). A wide variety of SAM-based supramolecular stmctures have been generated and used as functional components of materials systems in a wide range of technological appHcations ranging from nanoHthography (196,197) to chemical sensing (198—201). 

Analytical chemistry having an interdisciplinary character cannot set aside the attractive power and advances of supramolecular chemistry - the chemistry beyond the molecule or the chemistry of molecular assemblies and of intermolecular bonds as defined by Jean-Marie Lehn, who won the Nobel Prize in 1987. Recognition, reactivity, and transport, as well as self-assembly, self-organization and self-replication are the basic functional features of supramolecular species and chemistry. 

The main supramolecular self-assembled species involved in analytical chemistry are micelles (direct and reversed), microemulsions (oil/water and water/oil), liposomes, and vesicles, Langmuir-Blodgett films composed of diphilic surfactant molecules or ions. They can form in aqueous, nonaqueous liquid media and on the surface. The other species involved in supramolecular analytical chemistry are molecules-receptors such as calixarenes, cyclodextrins, cyclophanes, cyclopeptides, crown ethers etc. Furthermore, new supramolecular host-guest systems arise due to analytical reaction or process. 

Functional supramolecular materials, formation by self-assembly of phthalocyanins and porphyrazines 96CC2385. 

Sauvage, J. P. and Hosseine, M. W., Eds., Comprehensive Supramolecular Chemistry, Volume 9 Templating, Self-Assembly, and Self-Organization, Pergamon, Oxford, 1999. 

Pralle M.U., Whitaker C.M., Braun P.V., and Stupp S.I. Molecular variables in the self-assembly of supramolecular nanostructure. Macromolecules, 33, 3550, 2000. 

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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