Self-Assembly Macrocyclizations

The plot of Eq. [21] is useful to evaluate the maximum yield of a cyclic assembly obtainable with a given driving force (Fig. 6). 

From Eq. [21], it is easy to show that self-assembly can be virtually complete, that is, (C %)max 99%, when the condition in Eq. [23] is satisfied  

[23] is the second condition for self-assembly, namely, the condition of stability of the self-assembling macrocycle over the acyclic oligomers. This is an important relation showing that the required driving force for self-assembly directly depends on the number of monomer units constituting the cyclic oligomer. The plot in Fig. 6 illustrates this point, as well as the plots reported in Fig. 5 showing that only the plot relative to 

KEM = 1000 satisfies the condition in Eq. [23]. Fig. 5 also shows that the value of the monomer concentration [Mi]o is crucial to determine the stability of a cyclic assembly in solution. If the concentration is too low, the assembly lacks the driving force to form and thus only low-order linear oligomers wiU be present in solution on the other hand, if the concentration is too high, the cyclic assembly loses the competition with the linear polymer. The optimal monomer concentration is obtained by Eq. [22]. It is interesting to note that when the condition in Eq. [23] is satisfied, (C %)max 100% and the optimal monomer concentration reduces to ([Mi]o)max 0.1fiEM . From Eq. [21] and Fig. 6 it also appears that a cyclic assembly does not form to any significant extent at any concentration, that is, (C %)max 1%. if the condition in Eq. [24] is satisfied  

In Fig. 6, three regions are evidenced the region obeying Eq. [23] in which self-assembly can be complete in a given range of reactant concentration, that obeying Eq. [24] in which self-assembly cannot occur at any reactant concentration, and that in between the two above regions in which self-assembly can be partial at best. 

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Fujita, M. Self-assembled macrocycles, cages and catenanes containing transition metals in their backbones. In Comprehensive Supramolecular Chemistry Sauvage, J.-P., Hosseini, M. W., Eds. Elsevier Oxford, 1996, Vol. 9, pp 253-282. 

The first example of a self-assembled macrocyclic complex possessing cis-pro-tected Pd(ii) blocks is the tetranuclear square compound 25 (Figure 10.10) [66]. 

The theoretical treatment for the self-assembly of a molecular entity into rings or cages occurring under thermodynamic control is based on two fundamental physicochemical quantities the effective molarity (EM) of the intramolecular interaction of the cyclic n-mer and the value of the stability constant of the intermolecular interaction (fCinter) [5]. The following formula has been derived by Ercolani and allows calculation of the minimum value of the product fCinterEM to obtain a virtually complete self-assembled macrocycle at certain monomer concentration ... 

Increasing the number of hydrogen bonds and reducing the number of components is a strategy to construct robust self-assembled macrocycles, both... 

Tarkanyi G, Jude H, Palinkas G, Stang PJ (2005) Dynamic NMR study of the hindered Pt-NBipyridine rotation in metal directed self-assembled macrocycles. Org Lett 7 4971 1973... 

Scheme 8 Tetrameric and hexameric organotin self-assembled macrocyclic supermolecules...

It was predicted that, in the limit of an infinite value of there is a critical monomer concentration erne = nEM below which the solution is virtually solely composed of the self-assembled macrocycle and above which the concentration of the latter remains constant, with the excess monomer then producing only non-cyclic species. 

M. Fujita, Comprehensive Supramolecular Chemistry (Eds. J. L. Atwood, J. E. D. Davies, D. D. Macnicol, F. Vogtle, J.-M. Lehn), Self-assembled Macrocycles, Cages, and... 

Table 1. Association Constants for the Various Self-Assembled Macrocycles and Guests...

Figure 3. Dinuclear self-assembled macrocycles in the crystal structures of (a) 10 (b) 12 (c) 17 (d) 18. Two crystallographically independent macrocycles were found in the crystal structure of 18.

Molecular recognition via base-pairing in self-assembled macrocyclic and high-order ensemble synthesis, supramolecular polymer preparation, molecular cage construction, and energy and electron transfer modeling 07CSR314. 

Ercolani G. Physical basis of self-assembly macrocyclizations. J Phys Chem B. 1998 102 5699-5703. 

Figure 25 Self-assembly of 83 to form pentameric 84 and hexameric 85 macrocycles (a) FeCl2-4H20, MeOH, 25 °C, 24 h (left). TEM images of hierarchical self-assembled macrocycles 84 and 85 into fibers (center). Scale bars (a 500 nm b 100 nm c 500 nm d 100 nm). Space-filling models of 84 and 85 (e and f, respectively). Adapted with permission from Ref. 10CEJ1768. Copyright 2010 WiLEY-VCH Veriag GmbH Co. KOaA, Weinheim.

Figure 3.23 shows how it may be possible for a simple, self-assembling macrocycle based on a coordination compound to form an interlocked aggregate, in this case a catenane (mutually interlocked rings - Section 3.4.3). The formation of the macrocycle itself occurs when a linear ditopic ligand has its ends joined by a metal cation in a process which is reversible (Figure 3.23(a)). If, however, the macrocycle... 

Natural tubular assemblies show remarkable biological functions. For example, tubular shaped channels aid the transport of materials in and out of cells. Given that simple self-assembling macrocycles and disks form assemblies reminiscent of these biological structures, it is not surprising that they have been a very active area of research. 

Changing the position of the pyridyl component on the binaphthalene core provided yet another geometric variation of this theme, and Lin and coworkers have shown how such a strategy can lead to a range of self-assembled macrocycles of variable size and substitution such as 225-230 [80]. All macrocycles could be produced with either Pd(ii) or Pt(ii) linkages in good to excellent yield (>74%, in all cases) and all are highly luminescent in solution. 

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