Supramolecular solids, layered assemblies

Fascinating supramolecular structures have been identified in the solid state of triorganotin tetrazoles [294-296]. Nitrogen-tin interactions between adjacent molecules lead to supramolecular self-assembly of triorganotin derivatives into helical chains, 123, and of functionalized polytetrazoles, e.g. 124, into two-dimensional layers and three-dimensional networks with large channels. 

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]. 

Successive H-bond urea self-assembly of 4 and sol-gel transcription steps yield preferential conduction pathways within the hybrid membrane materials. Crystallographic, microscopic and transport data confirm the formation of self-organized molecular channels transcribed in solid dense thin-layer membranes. The ionic transport across the organized domains illustrates the power of the supramolecular approach for the design of continual hydrophilic transport devices in hybrid membrane materials by self-organization (Figure 10.8) [42-44]. 

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 solid 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 solid materials (193—195). A wide variety of SAM-based supramolecular structures have been generated and used as functional components of materials systems in a wide range of technological applications ranging from nanolithography (196,197) to chemical sensing (198—201). 

As pointed out in Chapter 1, supramolecular chemistry comprises two broad, partially overlapping areas covering on the one hand the oligomolecular supermolecules and, on the other, the supramolecular assemblies, extended polymolecular arrays presenting a more or less well-defined microscopic organisation and macroscopic features depending on their nature (layers, films, membranes, vesicles, micelles, microemulsions, gels, mesomorphic phases, solid state species, etc.). 

For the organization of coronene in heptanoic acid, the substrate material and/ or preparation procedure apparently matters Hipps and co-workers [141] investigated supramolecular assemblies of coronene with alkaline acids (hexanoic, heptanoic and octanoic) with STM also at the liquid-solid interface. While the dipole-dipole interactions produce bi-layers of one coronene molecule, which are surrounded by 12 acid molecules in the case of hexanoic and heptanoic acid, in octanoic acid, on the other hand, no solvent molecules are present in the coronene monolayer. 

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