Supramolecular polymers assembling mechanisms

Dramatic examples have also been reported for main-chain supramolecular polymers (SPs Lehn 1993 Ciferri 2005 Fig. 3.1), in which specific and directional molecular recognition events between end groups define the main chain of a linear polymeric assembly. Although main-chain SPs had been created and characterized previously (Broze et al. 1983 Fouquey et al. 1990 Alexander et al. 1993 Bladon and Griffin 1993 St Pourcain and Griffin 1995), it was a groundbreaking paper in 1997 that demonstrated the mechanical potential of supramolecular interactions and catalyzed much of the current interest in the field (Sijbesma et al. 1997). 

A number of dynamic supramolecular polymers control vital functions in biology. These are tightly regulated by highly selective and spatially confined catalytic mechanisms whereby non-assembling precursors are catalytically activated to produce self-assembling components. 

Supramolecular polymers are linear chains of low molar mass monomers held together by reversible and highly directional non-covalent interactions. In suitable experimental conditions, they can display polymer-like rheological or mechanical properties, because of their macromolecular architecture. However, the fact that non-covalent interactions are involved means that the assembly can be reversibly broken. This reversibility brings additional features compared to usual polymers, which can potentially lead to new properties, such as improved processing, self-healing behavior or stimuli responsiveness. 

Alternatively, the use of reversible, thermodynamically-controlled synthetic methods - similar to those used to make the supramolecular polymers discussed in Figure 1 - can be used to assemble mechanically interlocked molecules in near quantitative yields (Figure 7)." However, imlike the supramolecular systems, once formed (after removal of the catalyst) the mechanically interlocked structures are robust and cannot be destroyed without breaking a (strong) covalent bond ... 

By incorporating such motifs into handcuff -shaped monomers, it should be possible to combine some of the characteristics of supramolecular polymers - self-correcting, thermodynamically-controlled assembly - with the hallmark properties and stability of standard polymers with covalent backbones (Figure 8). Such monomers would, in the presence of a catalyst, spontaneously assemble to form mechanically linked polymers of precise length and architecture defined by the concentration at which they were prepared. Indeed, the various structures (linear, branched, hyperbranched etc.) would be intercon-... 

Fig. 24 Structure of a mechanoresptmsive metallo-supramolecular polymer network and schematic representation of (dis)assembly mechanisms, (a) Formation of (5)i j-[Eu(CI04)3] netwraks by assembly of 5 and Eu(C104)3-6H20 (C104 counterions are omitted for clarity), (b)...

Classification and Nomenclature of Supramolecular Compounds, p. 267 Clathrate Hydrates, p. 274 Crystal Growth Mechanisms, p. 364 Self-Assembly Definition and Kinetic and Thermodynamic Considerations, p. 1248 Self-Assembly in Biochemistry , p. 1257 Supramolecular Polymers, p. 1443... 

Fig. 1 Supramolecular donor (red) and acceptor (blue) self-assembled systems (a) infinite stack of donor and acceptor species (b) mechanically interlocked structure (c) linear supramolecular polymer and (d) cross-linked supramolecular polymer network...

Rudy J. Koopmans and Anton PJ. Middelberg, Engineering Materials from the Bottom Up - Overview Robert PW. Davies, Amalia Aggeli, Neville Boden, Tom C.B. McLeish, Irena A. Nyrkova, and Alexander N. Semenov, Mechanisms and Principles of 1 D Self-Assembly of Peptides into -Sheet Tapes Paul van der Schoot, Nucleation and Co-Operativity in Supramolecular Polymers MichaelJ. McPherson, Kier James, Stuart Kyle, Stephen Parsons, and Jessica Riley, Recombinant Production of Self Assembling Peptides... 

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