Synthesis supramolecular

Supramolecular, non-covalent, synthesis consists in the generation of supramolecular architectures through the designed assembly of molecular components directed by the physico-chemical features of intermolecular forces like molecular, covalent, synthesis, it requires strategy, planning and control. 

In the realm of synthetic chemistry, supramolecular synthesis thus pursues similar endeavours in planning and control on the intramolecular level as molecular synthesis does on the intramolecular one since it also requires the correct storage of an intermolecular project into a covalent framework, it necessitates expertise at both levels. 

As pointed out in Chapter 1, chemistry has just entered the confines of the supramolecular world and great feats in synthetic power for the elaboration of ever more complex non-covalent architectures lie ahead, just as there has been a rich and exciting but long way of tribulations from the synthesis of urea in 1828 to those of vitamin B12 [1.3, 1.4], palytoxin [9.177a], or calicheamicin [9.177b], to cite just a few major achievements in recent times [9.177c]. 

Newkome et al. prepared metallodendrimers with a ligand/metal/ligand architecture allowing separate construction of the dendrons. Two polyamide den-drons were preconstructed and linked to a ruthenium complex [38] (see Section 4.1.11). 

Further complex-chemical dendrimer syntheses ( metal-directed self-assembly utilising metal ions as convex templatef) are to be found in the literature [39]. 

In contrast to the methods already presented, the supramolecular synthesis [40b] of dendrimers [40b] does not involve covalent bond formation, but instead exploits non-covalent interactions. 

Frechet et al. were able to coordinate polyether dendrons having carboxylate functional groups at the focal point with lanthanide ions up to the fourth generation (Fig. 2.11) [41]. Preparation by straightforward ligand exchange starting from lanthanide triacetates with dendron carboxylates was made possible by the 

A dendritic two-component gelator was synthesised by Smith et al. on the basis of self-assembling acid-base/hydrogen bond interactions. Dendritic lysine building blocks serve as dendrons, and an aliphatic diamine as core (Fig. 2.12). Depending upon the choice of building blocks, the supramolecular complex forms fibrous gel phases by hierarchic self-organisation. 

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The use of DNA hybridization just described opens up a novel, uncomplicated, yet powerful strategy for supramolecular synthesis Many different devices are connected to a distinct sequence codon and are subsequently organized on a suitable template strand. The utilization of appropriate nucleic acid scaffolds should even allow the fabrication of highly complex supramolecular structures by means of a modular construction kit. For approximately 20 years, the work of Seeman and coworkers [8,27] have been engaged in the rational construction of ID, 2D, and 3D DNA frameworks. They use branched DNA... 

Indeed, we anticipate that the Platonic and Archimedean solids may be used for the construction of hosts which conform to those solids not yet realized and additional members of each family, where supramolecular synthesis, via self-assembly, will play a major role in their design, ushering in an era of spherical host-guest chemistry. 

Scherman OA, Ligthart GBWL, Ohkawa H, Sijbesma RP, Meijer EW. Olefin metathesis and quadruple hydrogen bonding a powerful combination in multistep supramolecular synthesis. Proc Natl Acad Sci USA 2006 103 11850-11855. 

Fig. 2.12 Dendritic two-component gelator produced by supramolecular synthesis (according to Smith et a/.) stereocentres are marked red...

Biological systems are fundamentally supramolecular in nature and provide much of the underlying inspiration for supramolecular synthesis in terms of the desire to mimic biological process such as enzyme catalysis, self-assembly and ion transport. 

This process involves the covalent locking in of structures formed by reversible self-assembly. The irreversible, post-assembly step switches off the equilibrium process involved in the self-assembly. As we will see in the following sections, self assembly with covalent postmodification is involved in a range of biochemistry (e.g. insulin synthesis) and elegant abiotic supramolecular synthesis as in the formation of catenanes and knots. 

Five helical strands associate laterally leading to a quintuple helical braid (Figure 29). The authors [49] suggested that the formation of this supramolecular assembly may be due to edge-to-face interactions between the pyridine units and the phenyl groups in conjunction with van der Waals interactions. Finally, the quintuple helices associate laterally to form the crystal. In this supramolecular synthesis H-bonding plays a role only in the first level of the assembly process via a single-stranded H-bonded helical network. 

However, crystal engineering did not become synonymous with supramolecular synthesis until die 1990s. As noted by J. S. Maddox in 19883 and more recendy by Gavezzotd17 and Ball,18 crystal structure prediction remains in its infancy. However, prediction is fundamentally very different from engineering and design. Predicting a crystal structure requires an analysis of the recognition features present in the molecular component in such... 

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