Self-reproducing micelles and vesicles

The system is symbiotic, and is considered the basis of co-evolution as such it has also been investigated by many authors from a theoretical point of view. An in-depth discussion is presented by Kauffman (1993). 

So far, only the self-replication mechanisms of linear molecules have been described it is now time to consider closed spherical structures, such as micelles and vesicles. Here, the term self-reproduction will be used rather than self-replication, because, as it will be seen, the population increase is generally based on statistical processes. The subject of micelles and vesicles self-reproduction is dealt with in other chapters in this book a certain degree of repetition and/or mis-match is unavoidable. 

The work was experimentally initiated in my laboratory in Zurich in the 1980s, at a time in which I was very much involved with reverse micelles - and in fact reverse micelles were the first spherically closed system that underwent self-reproduction. 

A few systems of this kind were developed (Bachmann, 1990 and 1991), and this allowed the introduction of the notion of self-reproducing micelles. The 

In general, the mechanism of self-reproduction of micelles and vesicles can be considered an autopoietic mechanism, since growth and eventually division comes from within the structure itself. This point will be considered again in Chapter 8, on autopoiesis, where the mechanism of the self-reproduction process will also be discussed. 

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We have also learned that self-replication is not a prerogative only of nucleic acids, but it can be shared by different kinds of chemical families see the formose reaction, the self-replicating peptides, and the self-reproducing micelles and vesicles. The list should include the cellular automata and the corresponding devices of artificial life. Self-reproduction of vesicles and liposomes is important because it represents a model for cell reproduction. 

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. 

A and B, which could react inside the boundary (but not outside) to yield as a product the very surfactant that builds the boundary (Luisi and Varela, 1990). In Chapter 7 it was also indicated how this theoretical paper led to the experimental implementation of self-reproducing reverse micelles, aqueous micelles, and vesicles (Bachmann et al., 1990, 1991, 1992 Luisi, 1994 Walde et al., 1994b). 

Of all mentioned prebiotic membranogenic molecules, the ones that have gained more attention in the literature are long-chain fatty acids. In addition to their prebiotic relevance, these compounds are relatively simple from the structural point of view, and most of them are easily available. We will see in the next chapter that these vesicles have acquired a particular importance in the held of the origin of life. In fact, the hrst inveshgations on self-reproducing aqueous micelles and vesicles were carried out with caprylate (Bachmann et al, 1992) and most of the recent studies on vesicles involve vesicles from oleic acid/oleate (for simplicity we will refer to them as oleate vesicles). In this section, I would like to illustrate some of the basic properties of these surfactant aggregates. 

Walde, R, Goto, A., Monnard, P.-A., Wessicken, M., and Luisi, P. L. (1994a). Oparin s reactions revisited enzymatic synthesis of poly(adenylic acid) in micelles and self-reproducing vesicles. J. Am. Chem. Soc., 116, 7541-7. 

Figure 8 Self-organization structures of block copolymers and surfactants spherical micelles, cylindrical micelles, vesicles, fcc-and CC-packed spheres (FCC, BCC), hexagonally packed cylinders (HEX), various minimal surfaces (gyroid, F surface, P surface), simple lamellae (LAM), as well as modulated lamellae (MLAM) and perforated lamellae (PLAM). (Reproduced from Ref. 28. Wiley-VCH, 2002.)...

Fig. 36.2 (a) Self-assembly of CP6 modified AuNPs with hydrophobic chain functionaiized paraquat into various hybrid nanostmctures. (b) Seif-assembly of CP6 stabiiized nanorod, NIR-triggered vesicle-to-micelle transition and reiease of the eneapsulaled calcein (Ref. [28], Copyright 2014 - Reproduced by permission of The Royai Soeiety of Chemistry)... 

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