Programmed supramolecular assembl

Programmed Supramolecular Assembly Precise molecular recognition between molecules produces a well-defined complex. Multiple complex formation therefore leads to a supramolecular assembly with a defined shape and structure. The structure of the supramolecular assembly formed can be regarded as being programmed by structural information in the unit structure. 

In addition to high efficiency, selectivity and cooperativity, another basic feature characterizing programmed supramolecular processes is self-recognition — the recognition of like from unlike, of self from non-self — embodied in the spontaneous selection and preferential assembly of like components in a mixture. 

The intention is not to comprehensively review the literature that describes the multidisciplinary efforts of researchers to create interfacial supramolecular assemblies. The literature in this area is vast and involves research programs in chemistry, physics and biology, as well as analytical, materials and surface sciences. Rather, key examples of advances that have significantly influenced the field and will direct its future development are presented. In addition, some of the analytical methods, theoretical treatments and synthetic tools, which are being applied in the area of interfacial supramolecular chemistry and are driving its rapid development, will be highlighted. 

We have seen that multiple use of a precise recognition process leads to well-designed supramolecular assemblies. The structure of the assembly formed is programmed in the original pieces. Highly precise design of the recognition pair should lead to the formation of a precisely defined structure. Such... 

In the realm of supramolecular synthesis, the construction of rack, ladder, and grid architectures represents a particular case of self-assembly, which relies on the three basic levels of operation of a programmed supramolecular system recognition (selective interaction of complementary components) orientation (building up the stmcture through the con ect spatial disposition of the components) and termination, that is, the formation of the desired discrete supramolecular entity. "... 

Since the mid-eighties, the term supramolecular chemistry has come to signify the programmed self-assembly of complex architectures through the interplay of noncovalent interactions. " In the case of the dimerization of cinnamate derivatives, Beak and Ziegler presented, over 20 years ago, the first example of the use of hydrogen bonding in solution to accelerate the usually inefficient cycloaddition reaction. In their work, the self-complementary pyridone unit was used to direct the head-to-head dimerization of the appended cinnamate moieties. 

Finally, to produce the structural and functional devices of the cell, polypeptides are synthesized by ribosomal translation of the mRNA. The supramolecular complex of the E. coli ribosome consists of 52 protein and three RNA molecules. The power of programmed molecular recognition is impressively demonstrated by the fact that aU of the individual 55 ribosomal building blocks spontaneously assemble to form the functional supramolecular complex by means of noncovalent interactions. The ribosome contains two subunits, the 308 subunit, with a molecular weight of about 930 kDa, and the 1590-kDa 50S subunit, forming particles of about 25-nm diameter. The resolution of the well-defined three-dimensional structure of the ribosome and the exact topographical constitution of its components are still under active investigation. Nevertheless, the localization of the multiple enzymatic domains, e.g., the peptidyl transferase, are well known, and thus the fundamental functions of the entire supramolecular machine is understood [24]. 

The number of building blocks for supramolecular self-assembly is virtually unlimited. Chapter 6, by Brunsveld, Rowan, Nolte, and Meijer, describes studies on disk-shaped molecules which are programmed to stack in a helical fashion, leading to novel kinds of twisted fibers as well as lyotropic and thermotropic liquid crystalline materials. 

Similarly, when a mixture of the two tris-bipyridine ligands 129 and 148 is allowed to react simultaneously with copper(l) and nickel(il) ions, only the double helicate 132 and the triple helicate 149 are formed (Figure 49). Thus, parallel operation of two programmed molecular systems leads to the clean self-assembly of two well-defined helical complexes from a mixture of their four components in a process involving the assembly of altogether 11 particles of four different types into two supramolecular species. 

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