Supramolecular self-replication

The following sections contain a review of many of the varied synthetic systems that have been developed to date utilising noncovalent interactions to form assembhes of molecules. These sections are loosely demarcated according to the most important type of noncovalent interactions utilized in conferring supramolecular order (ie, van der Waal s interactions, electrostatic interactions, and hydrogen bonds). For extensive reviews, see References 1,2,4—6,22,46,49,110—112. Finally, the development of self-assembling, self-replicating synthetic systems is noted. 

Analytical chemistry having an interdisciplinary character cannot set aside the attractive power and advances of supramolecular chemistry - the chemistry beyond the molecule or the chemistry of molecular assemblies and of intermolecular bonds as defined by Jean-Marie Lehn, who won the Nobel Prize in 1987. Recognition, reactivity, and transport, as well as self-assembly, self-organization and self-replication are the basic functional features of supramolecular species and chemistry. 

Self-replication, in supramolecular chemistry, 24 49-50 Self-rising flours, 26 281-282, 283 Self-sensing, in rheometers, 21 737 Self-supporting structures, artificial graphite in, 12 745 Self-warming baby milk bottle... 

So, how close have supramolecular chemists come to realizing a self-replicating system The answer is not too close. There are few chemists currently working on the problem from a perspective of a system based on supramolecular chemistry. One requirement of any system designed to perpetuate information is that it must encode a large amount of information. In the DNA/RNA system it is in the form of... 

Nguyen R, Allouche L, Eric Buhler E, Giuseppone N (2009) Dynamic combinatorial evolution within self-replicating supramolecular assemblies. Angew Chem Int Ed 48 1093-1096... 

The stereochemical shape concept covers a wide range of possible resolutions, from the details of electron density distributions between pairs of nuclei in relatively small molecules to the structural organization of the tertiary structure of proteins [201-203], the architecture of supramolecular assemblies [204-230], the problems of shape selectivity in reactions of large molecules [231-233], and the intriguing shape features of self-replicating chemical systems [234-239]. In the following chapters we shall discuss various topological shape analysis techniques, suitable for the relevant level of resolution. 

Clearly, molecular recognition processes are the prototypical supramolecular reactions on which the other aspects are based. Without molecular recognition, there are no template effects, no self-assembly, and certainly no self-replication. In contrast to opinions sometimes encountered among chemists from other areas, supramolecular chemistry did not come to a halt with the examination of hosts and guests and their interactions. Sophisticated molecular devices are available which not only are based on, but go far beyond mere molecular recognition. 

Later, suitable a-helical peptides have been shown to self-replicate as well [42]. In the context of supramolecular chemistry most interesting are however organic minimal-replicators [43] which are not based on biomolecules. Figure 1.5 shows an example for a minimal self replicating system, which operates even in a chiro-selective way. One given enantiomer of the template catalyzes its own formation, while the other enantiomer is by and large suppressed. 

We have mentioned before the possibility of combining chemical evolution with self-replication. In principle, chemical evolution can be associated to self-reproducing micelles or vesicles. There are in principle two ways to conceive this in this case on the one hand, the surfactants of the self-reproducing vesicles could be chemically transformed during their reproduction cycles into compounds which may give rise to more efficient cell-like compartments. This possibility has been discussed theoretically some time ago. On the other hand, the supramolecular structure can help and determine the evolution of internalized compounds—i.e. permitting certain reactions and avoiding others thanks to the semipermeable character of the membrane. As already mentioned, studies of this type with vesicles still remain to be initiated. 

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