Thermodynamic self-assembly

Torelli, S., Delahaye, S., Hauser, A., et al. (2004) Ruthenium(II) as a novel labile partner in thermodynamic self-assembly of heterobimetalhc d-f triple-stranded helicates. Chemistry — A European Journal, 10, 3503. 

Several types of self-assembly have been identified from the biological literature 7 (i) thermodynamic self-assembly (ii) irreversible self-assembly (iii) assisted and directed self-assembly and (iv) self-assembly with pre-, post-, or intermittent modification. 

The most important and widely used assembly technique in designed synthesis is thermodynamic self-assembly. Because product selection in such processes is dependent on thermodynamic stability, the key to using this class of self-assembly as a synthetic tool is to ensure that the desired product will be more stable than any possible competing product. This is achieved by reverse engineering the assembly components so that the desired structure is selectively favored. The greater its stability relative to its competitors, the greater will be its proportion in solution. 

Another important characteristic of thermodynamic self-assembly is the relative influence of enthalpy and entropy. Because of the large bond energy involved in coordination, enthalpy constitutes the main driving force for all thermodynamic self-assembly involving coordination... 

Two self-assembly techniques are predominantly employed in the preparation of catenanes "thermodynamic" self-assembly and self-assembly with covalent "modification."... 

Thermodynamic self-assembly involves the establishment of a dynamic equilibrium between the reagents and products in which catenane structures are energetically highly favored. If such systems are kinetically labile, the products obtained in greatest proportions will be those that are also the most thermodynamically stable that is. catenane structures. In such processes, thermodynamic influences drive the cyclization and the interlocking steps required in the formation of catenanes. Different types of... 

Illustrated in Fig. 2 is one of the most famous examples of a metal-mediated, thermodynamically self-assembled catenane. The reaction of 1 (M = Pd) with the angled bipyridyl ligand 2 was found by Fujita and coworkers to lead to the formation of cycle 3, along with the interlocked catenane The nature of the self-assembly process... 

Fig. 2 Thermodynamic self-assembly Formation of a [2]-catenane. mediated by coordinative and other noncovalent interactions.

While the simultaneous use of several different classes of noncovalent interactions provides an elegant means of preparing a catenane. such systems are not always easily designed. Another method of thermodynamically selfassembling catenanes involves using two or more metal-mediated interactions to carry out the cyclization and interlocking steps. Illustrated in Figs. 3 and 4 are examples of thermodynamic self-assembly of this type. 

Fig. 7 Thermodynamic self-assembly of multiring catenanes— Molecular necklaces. Formation of a [4]MN, mediated by co-ordinative and other noncovalent interactions.

Fig. 8 Thermodynamic self-assembly of a polycatenane. Formation of a linear poly[2]catenane containing covalent, topological, and...

In this article, the various terminologies used to describe important concepts in thermodynamic self-assembly will be reviewed. In so doing, an attempt is made to illustrate, wherever possible, the underlying unity of the concepts and eliminate confusion arising from the different terminologies used. Most of the terminologies derive from the fields of chemistry, biology, and biochemistry. 

Fig. 34.11 Force-distance curves between two NPs with diameter d, coated with surfactant layers having separatirui s between chains of length L [18]. Thermodynamic self-assembly can be achieved when Iruig-range vdW attraction (red) is countered by short-range steric repulsion (green), which gives rise to a secondary minimum that defines the optimum distance between NPs in their self-assembled state (Reprinted with pmnission from the Royal Society of Chemistry)...

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