Other Self-assembly Examples

The examples highlighted in this section illustrate the broad applicability of fibrils and other self-assembling systems as components in biosensors... 

Polymerization of LB films, or deposition of LB films on polymers, offers the opportunity to impart to LB films a higher degree of mechanical integrity. However, preliminary work in this direction shows a conflict between the chainlike primary structure of the polymer and the well-organized supramo-lecular structure [15]. One possible solution may be the insertion of flexible spacers between the main chain polymer and the side chain amphiphile, a route also employed in liquid crystal polymers. These materials belong to an interesting class of two-dimensional polymers, of which there are few examples. These toughening techniques may eventually be applied to stabilize other self-assembled microstructures, such as vesicles, membranes, and microemulsions. 

Other self-assembly approaches have been applied in order to obtain polynuclear metallacycles for potential medical applications, for example, counterion encapsulation [84] or use as organometallic ionophores [85] employing halfsandwich Ru(II), Rh(III), or Ir(III) building blocks. Despite the fact that some of these species have a chiral environment around the metal, studies of comparative cytotoxicity between single homochiral or heterochiral systems have not been carried out as yet. 

As materials chemistry has developed, it has come to pay more and more attention to that archetypal concern of materials scientists, microstructure. That concern came in early when the defects inherent in non-stoichiometric oxides were studied by the Australian. I.S. Anderson and others (an early treatment was in a book edited by Rabenau 1970), but has become more pronounced recently in the rapidly growing emphasis on self-assembly of molecules or colloidal particles. This has not yet featured much in books on materials chemistry, but an excellent recent popular account of the broad field has a great deal to say on self-assembly (Ball 1997). The phenomenon of graphoepitaxy outlined in Section 10.5.1.1 is a minor example of what is meant by self-assembly. 

Some of the more remarkable examples of this form of topologically controlled radical polymerization were reported by Percec et cii.231 234 Dendron maeromonomers were observed to self-assemble at a concentration above 0.20 mol/L in benzene to form spherical micellar aggregates where the polymerizable double bonds are concentrated inside. The polymerization of the aggregates initiated by AIBN showed some living characteristics. Diversities were narrow and molecular weights were dictated by the size of the aggregate. The shape of the resultant macroniolecules, as observed by atomic force microscopy (ATM), was found to depend on Xn. With A, <20, the polymer remained spherical. On the other hand, with X>20, the polymer became cylindrical.231,232... 

A huge number of transition metal-sulfur clusters have been synthesized,36 most of which have been obtained based on the self-assembly methods. On the other hand, to construct the cluster cores with the desired metal-sulfur compositions and connecting schemes, rational pathways leading to the high-yield syntheses of tailored metal-sulfur clusters have recently been explored. Fragment condensations have been demonstrated to be the powerful methods to obtain such clusters numerously,37 some examples of which are shown below. 

Other common techniques have been applied to the assembly of layers or films of TTF-derived molecular conductors. Compound 29 is an example of an amphiphilic TTF derivative. It forms conducting Langmuir-Blodgett charge transfer films with the acceptor TCNQF4 (30).98 Self-assembly of compound 31 on gold by electrochemical methods yielded an electroactive monolayer which was remarkably stable to electrochemical cycling.99... 

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