Strict self-assembly examples

The most famous example of a strict self-assembly process is the formation of the DNA double helix (Figure 2.27), by the spontaneous association (by hydrogen bonding) of complementary... 

Coordination interactions are not the only way to use self-assembly to produce closed, capsular systems capable of binding guest species in solution. Work by Julius Rebek Jr (Scripps, USA)43 has shown that multiple hydrogen-bonding interactions, because of their relatively weak, but directional, nature, are ideal for the strict self-assembly of closed spherical molecules and capsules. For example, component 10.49 consists of two intrinsically curved diphenylglycoluril units linked by a durene-based (1,2,4,5-tetramethyl benzene-based) spacer. In both solution and in the solid state, 10.49 self-assembles spontaneously to produce the tennis ball-shaped dimer (10.49)2 shown in Figure 10.43. The formation of the dimer has been observed by ... 

Recently, a third process has been identified which constitutes an example of strict self-assembly.The so-called slippage approach to rotaxane synthesis Figure 5) is based upon size complementarity between the macrocyclic polyether, BPP34C10, containing two 7i-electron rich recognition sites and the stoppers comprised of suitable tetra-arylmethane groups at the ends of dumbbell-shaped molecules incorporating at least one 4,4 -bipyridinium unit. ... 

In the previous chapters, examples of ID arrays of nanoclusters have been given, where self-assembly or ET were used to address the arrays for electrical transport measurements. So far it is evident that these methods did not lead to strictly ID defect-free arrangements. Furthermore, inherent disorder cannot be avoided. This means that the electrical transport properties through a perfect array could only be studies theoretically up to now. 

Caspar and Klug (1962) made an important distinction between two fundamental types of assembly processes. True self-assembly was conceptualized as a series of reactions relying on the propensity of subunits to condense and form assembled structures strictly as a result of the information encoded in the architecture of the components. On the other hand, template-directed assembly may be considered as a process depending on the presence of a separate template that imparts structural constraints on the pathway for constructing the final assembled structure. True self-assembly is observed, for example, in the formation of many oligomeric proteins. Indeed, Friedman and Beychok (1979) have re-... 

Although not strictly LB films, there are other types of self-assembled films containing Q-state MCs that resemble LB films. One example involves the self-assembly of the amphiphile DTG into an organized film by slow evaporation of solvent from a dispersion of the amphiphile (40). The structure of the cast film has the head-... 

The structures mentioned up to this point have represented examples of quasizero-dimensional (0-D) systems, in which self-assembly or electrostatic trapping are used to place the individual (or at least a few) partides into a nanogap for electrical transport measurements. However, the processes are not necessarily suited to electrically address a well-defined number in a desired arrangement in a reliable maimer, which in turn means that neither method can lead to strict and defect-free 1-D arrangements. In addition, inherent disorder cannot be avoided. Thus, until now, the electrical transport properties through a perfect 1-D array have been studied on a theoretical basis. 

The latter example leads us to still another characteristic feature of supramolecular concepts i.e., their hierarchical assemblies allow functional materials. Functionality is regarded as one of the hallmarks of supramolecular science [13] as even in classical chemistry and self-organization, complexes, salts, etc. are formed due to chemical matching. One can point out that the borderline between classical chemistry and supramolecular chemistry is not strict. For example, in general block copolymers dissolved in block-selective solvents might not be regarded as supramolecular chemistry, whereas some of the more specific further developments [18, 82] clearly allow supramolecular functional materials, as will be shown in Section 3. 

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