Self-assembly architectures

Synthetic self-assembled architecture and evolutionary implications... 

The layer thickness usually depends on the compounding module s size and an accurate metric engineering can be done according to which the length of starting module determines the thickness of the layer. This holds for self-assembled architectures wherein the XB acceptor is both an anionic [ 189] (Fig. 13) and a neutral tecton [168]. 

Fig. 13 Self-assembled architectures wherein the XB acceptor is I- and the donors are differently sized a//j-diiodoperfluoroalkanes. The layer thickness depends on the size of the XB donor module, thus allowing an accurate metric engineering of the layers to be realized...

In practice, as the properties of a (nano)material emerge from the composition, size, shape and surface properties of these individual building-blocks as well as self-assembled architectures made from these building-blocks, chemists are increasingly able to synthesize tailor-made materials from the bottom up. Such techniques generally rely on... 

ReifJ (ed)(2004) Foundations of nanoscience Self-assembled architectures and devices (FNANO 2004), Snowbird, Utah, 21-23 April 2004. ScienceTechnica (http //www. cs.duke.edu/ reif/FNANO/FNAN004/)... 

Reynhout, I. C., Cornelissen, J., Nolte, R. J. M., Self-assembled architectures from biohybrid triblock copolymers. J. Am. 

Besides metallocycles, metallodendrimers, and metallo-supramolecular polymers [58], few examples of hollow supramolecular architectures have been obtained from polytopic ligands containing terpyridine units. Lehn et al. used heteroaromatic ligands with terpyridine type coordination sites to obtain cylindrical self-assembled architectures (Fig. 11) [60]. For synthesis of the cage 37, tris-2,4,6-(2-pyrimidyl)-l,3,5-triazine (35) was mixed with lead triflate in... 

A key feature of stable self-assembled architectures is positive cooperativity, in which each step in the self-assembling process sets up and facilitates the subsequent step. In a rational design of triple-helical clusters, a series of bisfcatecholamide) ligands (H4L") 50-52 have been synthesized (Scheme 6). When three equivalents of any of these ligands are allowed to react with two equivalents of M(acac)3 (M = Fe +, aF+, Ga +) and KOH in methanol, the [K M2L"3] triple helicates... 

Scheme 1, is given the description A2 L3 . Examples of self-assembled A4 and mlxed-assembled structures are complex (1) and (2) respectively. Clearly these descriptors provide valuable information, at a glance, about the building units and their modes of binding in the self-assembled architectures. 

The metal-mediated synthetic approach has recently provided many examples of large discrete assemblies of porphyrins [39-41] and of solid-state arrays as well [39-48]. For the purpose of metal-driven synthesis, porphyrins and metal centers are to be considered essentially as rigid modules. Thus, in principle, the final shape, dimension, and topology of the self-assembled architecture will be defined by the number and relative geometries of the coordination sites on the building blocks. Within this framework, meso-pyridylporphyrins (PyPs, Fig. 1) are largely exploited as they can provide... 

Lehn has described supramolecular chemistry as an information science molecular subunits which contain the necessary information self-assemble into a larger specific structure. Complementary and explicit interaction of individual components with the appropriate symmetry and geometry generates the product assembly. In terms of coordination chemistry, astute ligand design and judicious choice of metal center allow one to access complex self-assembled architectures, many in the nanometer regime. 

These common features suggest that self-assembling process is actually a complex yet organized process mediated by many factors, which in turn should be carefully considered in the manufacture of self-assembled architectures. Specifically, these crucial factors include (but are not limited to) molecular (or component) mobility, proximity to equilibrium, and anisotropy [5]. Mobility refers to the ability of molecules or components to change position and orientation, which is usually... 

In the following sections, self-assembled architectures based on the two main peptide secondary structures (a-helices and /S-sheets) are discussed. This is followed by some examples of fiber formation constituted by dipeptide... 

Alkanes are also widely employed as functional groups in other gelation systems. Appending alkanes onto a variety of molecular frameworks provides an opportunity to introduce van der Waals interactions (both within and between fibrils), as well as tuning the overall solubility of the gelator and, consequently, the solvent compatibility of the self-assembled architecture. 

Overall, the potential uses of these cross-linked materials are improved by their increased stability toward environmental changes such as concentration and temperature, compared to their non-cross-linked micellar precursors. The subsequent selective and reversible attachment of moieties to the cross-linked self-assembled architectures further extends the potential application of these materials toward their development as well-defined polymeric supports which can behave as controlled release vessels. However, a significant disadvantage of such materials is their sometimes difficult and time-consuming preparation, which is not ideal for large industrial scale applications. 

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