Self-directed assembl

Figure 13.5. Supramolecular structures formed by self-directed assembly in trans left) or cis right) forms.

Liu NG, Yu K, Smarsly B, Dunphy DR, Jiang YB, Brinker CJ. 2002. Self directed assembly of photo active hybrid silicates derived from an azobenzene bridged silses quioxane. J Am Chem Soc 124 14540 14541. 

Finally, the synthesis of PMOs involving surfactant-directed self-assembly and self-directed assembly allows reaching a multiscale structuration of the material with controlled optoelectronic properties. 

More recently, a new method of assembling multilayers of PB on surfaces has been described.110 In contrast to the familiar process of self-assembly, which is spontaneous and leads to single monolayers, directed assembly is driven by the experimenter and leads to extended multilayers. In a proof-of-concept experiment, the generation of multilayers of Prussian blue (and the mixed Fein/Run analog ruthenium purple) on gold surfaces by exposing them alternately to positively charged ferric cations and [Fe(CN)6]4- or [Ru(CN)f,]4 anions has been demonstrated.110... 

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-... 

The spontaneous self-assembly or template-directed assembly of component monomeric units into polymeric biological macromolecules. 2. The enzyme-catalyzed joining of monomeric units (such as amino acids, sugars, nucleotides) into covalently linked oligomeric or polymeric forms. 

Self- and Directed-Assembly of Chiral Pt-Alkynyl Metallocycles 101... 

There is no clear understanding at this point of the parameters that dictate the cases for which self-assembly will be superior to externally directed assembly . For numerous, small components, self-assembly will probably always be superior for unsymmetrical patterns with relatively large components (e.g., microelectronic circuits) top-down fabrication will probably remain superior. In problems involving intermediate sizes and intermediate numbers of components, it remains to be seen which strategy is best. Pick-and-place assembly with 100-nm components will never be straightforward practically, although it may find uses in research. 

The introduction of SAMs on localized areas of a substrate allows straightforward further functionalization and directed assembly of nanoparticles. By using chemistry, specific binding can be introduced, allowing the control of nanoparticle assembly onto lithographic patterns. Wet-chemical self-assembly of nanoparticles is particularly attractive for the fabrication of nanoparticle-based nanostructures because of its compatibility with various kinds of substrates with complex shapes. In this section, conventional and nonconventional patterning techniques for the chemical assembly of nanoparticles will be highlighted. 

As scientists and engineers, natural self-assembly processes represent a tremendous resource, which we can use to create our own miniature materials and devices. Our endeavors are informed by hundreds of years of curiosity-driven research interested in the natural world. Our toolbox is further expanded by modem synthetic chemistry which extends beyond the realm of natural molecules. We can also create artificial environments to control and direct assembly and use computer-based tools and simulations to model and predict self-assembly pathways and their resulting protein structures. Many researchers believe we can use these modern tools to simplify, improve, and refine assembly processes. We have much to do in order to reach this ambitious goal but the next 10 years are likely to be filled with exciting discoveries and advances as self-assembling polypeptide materials move from the laboratory to the clinic or the manufacturing assembly line. 

All cellular life today incorporates two processes we will refer to as self-assembly and directed assembly (Fig. 1). The latter involves the formation of covalent bonds by energy-dependent synthetic reactions and requires that a coded sequence in one type of polymer in some way direct the sequence of monomer addition in a second polymeric species. On the other hand, spontaneous self-assembly occurs when certain compounds associate through noncovalent hydrogen bonds, electrostatic forces, and nonpolar interactions that stabilize orderly arrangements of small and large molecules. Three well-known examples include the self-assembly of water molecules into ice, DNA... 

Since the structure of DNA was first revealed by Watson and Crick in 1953, the formation of the double helix of nucleic acids by a self-directing, co-operative process has fascinated several generations of scientists. In general terms, DNA may be seen to self-assemble by a process in which two long chain polytopic receptors interact with the base pairs in such a way that each association step sets the stage for the one that follows. 

Lin Y et al (2005) Self-directed self-assembly of nanoparticle/copolymer mixtures. Nature 434(7029) 55-59... 

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