Self-assembly information-directed

Self-assembled template-directed systems containing reactive groups provide pathways towards systems displaying copying, information transfer and replication. This may lead to spontaneous condensations within the self-assembled entity into the final covalent structure. A special case is the reproduction of the template itself by replication or self-... 

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-... 

In excerpt I5D, Walker begins with a statement of the topic (solvation at hydrophobic and hydrophilic solid-liquid interfaces) and then moves directly to the signihcance of the work. He emphasizes the need for information on interfacial phenomena and points out possible applications of his work for other areas of science (molecular recognitions, electron transfer, and macromolecular self-assembly). He goes on to describe his experimental methods, focusing on three aspects of his approach (in order of difficulty) equilibrium measurements, time-resolved studies, and distance-dependent measurements of solvation strength. 

The Gibbs adsorption theory (Birdi, 1989,1999, 2002, 2008 Defay et al., 1966 Chattoraj and Birdi, 1984) considers the surface of liquids to be monolayer. The surface tension of water decreases appreciably on the addition of very small quantities of soaps and detergents. The Gibbs adsorption theory relates the change in surface tension to the change in soap concentration. The experiments that analyze the spread monolayers are also based on one molecular layer. The latter data indeed conclusively verifies the Gibbs assumption (as described later). Detergents (soaps, etc.) and other similar kind of molecules are found to exhibit self-assembly characteristics. The subject related to self-assembly monolayer (SAM) structures will be treated extensively (Birdi, 1999). However, no procedure exists that can provide information by direct measurement. The composition of the surface of a solution with two components or more would require additional comments. 

The formal potential, E0/, contains useful information about the ease of oxidation of the redox centers within the supramolecular assembly. For example, a shift in E0/ towards more positive potentials upon surface confinement indicates that oxidation is thermodynamically more difficult, thus suggesting a lower electron density on the redox center. Typically, for redox centers located close to the film/solution interface, e.g. on the external surface of a monolayer, the E0 is within 100 mV of that found for the same molecule in solution. This observation is consistent with the local solvation and dielectric constant being similar to that found for the reactant freely diffusing in solution. The formal potential can shift markedly as the redox center is incorporated within a thicker layer. For example, E0/ shifts in a positive potential direction when buried within the hydrocarbon domain of a alkane thiol self-assembled monolayer (SAM). The direction of the shift is consistent with destabilization of the more highly charged oxidation state. 

As with all supramolecular structures, one of the most important issues is whether a direct relationship between the structure of a material and its function or properties can be established. In the following, some examples of polymer systems which show such a correlation will be discussed. The materials addressed will include block copolymers, polyalkylthiophenes and a multilayer system based on the self-assembly of polyelectrolytes. Detailed studies on the electrochemical properties of redox-active polymers, based on poly(vinyl pyridine) modified with pendent osmium polypyridyl moieties, have shown that electrochemical, neutron reflectivity and electrochemical quartz crystal microbalance measurements can yield detailed information about the structural aspects of thin layers of these materials. 

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. 

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