Dynamic combinatorial materials

Consequently, supramolecular materials are by nature dynamic materials, defined as materials whose constituents are linked through reversible connections (covalent or noncovalent) and undergo spontaneous and continuous assembly/disassembly processes in a given set of conditions [47], Because of their intrinsic ability to exchange their constituents, they also have combinatorial character so that they may be considered as dynamic combinatorial materials (DCMs). Supramolecular materials thus are instructed, dynamic, and combinatorial, they may in principle select their constituents in response to external stimuli or environmental factors and therefore behave as adaptive materials [45],... 

Dynamic Chemistry. Supramolecular Materials Programmable, Dynamic, Combinatorial Materials... 

It follows from the previous considerations that supramolecular polymer chemistry is both dynamic and combinatorial and that supramolecular polymers are therefore dynamic combinatorial materials based on dynamic libraries whose constituents have a combinatorial diversity determined by the number of different monomers (see Section III). Similar views apply to supramolecular liquid crystals. 

Figure 8.1 A dynamic combinatorial library on the preparation of polymer materials bearing reversible linkages.

Dynamic combinatorial chemistry in drug discovery, bioorganic chemistry, and materials science / Benjamin L. Miller, p. cm. 

Fig. 6 Dynamic combinatorial peptide library that expioits enzyme reactions to control self-assembly processes under thermodynamic controi. (a) Emergence of the potentiai peptide derivatives of varying length in a library of interconverting molecules formed from the staring materials of Fmoc L/L2 system. Fmoc-Ls is preferentially formed. Corresponding AFM images of the fibrillar structures formed at 5 min after the addition of enzyme, and the sheet-like structures observed after 2000 h show that redistribution of the derivatives is accompanied by the remodelling from fibres (Fmoc L3) to sheet-like structures (Fmoc L5). (b) HPLC analysis of the composition of the system reveals the formation and the stabilisation of Fmoc-Ls over time. Modified from [21]...

Moreover, reversible covalent changes (e.g. due to dynamic imine bonds) are of importance within the area of dynamic combinatorial chemistry, where they can serve as basis for the design and operation of functional materials and devices [86]. 

Moulin E, Cormos G, Giuseppone N (2011) Dynamic combinatorial chemistry as a tool for the design of functional materials and devices. Chem Soc Rev. doi 10.1039/clcsl5185a... 

In addition, to the extension to materials science, one may envisage the implementation of dynamic combinatorial approaches in other areas. 

The use of anions as templating agents is discussed by Vilar. The chapter starts with a general overview of the area and a discussion of the applications of anion templates in organic and coordination chemistry. The second part of the chapter deals with examples where anions are employed as templates in dynamic combinatorial libraries. This approach promises to provide an efficient route for the synthesis of better and more selective anion receptors. The last chapter by Ewen and Steinke also deals with the use of anions as templates but in this case in the context of molecular imprinted polymers. The first half of the chapter provides an introduction into molecularly imprinted polymers and this is followed by a detailed discussion of examples where anionic species have been used to imprint this class of polymeric materials. 

No successful example has been reported so far using a TSA in a dynamic combinatorial approach to transition metal catalyst selection. However, inspired by enzymes and molecular cages, molecularly imprinted polymers were successfully developed by WuUF et al. and in a small number of cases directed towards transition metal catalysis [22]. Cavities as biomimetic catalysts are created by generation of polymeric materials in the presence of a TSA as a template, which is removed after polymerization. In the presence of the substrate, the incorporation of the catalyst precursor leads to high activities, the transition state being stabilized by the polymeric cavities. 

The basic concepts of selection experiments with dynamic combinatorial libraries (DCLs) were articulated more than 10 years ago (see Chapter 1). Since then, a number of applications have emerged. This includes the discovery new enzyme inhibitors, receptors, and catalysts, as well as the synthesis of novel materials such as responsive gels and polymers (see Chapters 2-5). A recent addition to the list of applications is the utilization of dynamic combinatorial chemistry (DCC) for analyhcal purposes. This chapter summarizes the main ideas and results in this area. 

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