The case of oleate vesicles

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. 

The cac (critical aggregate concentration) values for oleate are in the millimolar range, which means that at the operational concentration of 10-50 mM there will be a signihcant concentration of monomer in equilibrium with the aggregate. This consideration allows us to go back to the question of whether vesicles are chemical equilibrium systems. Oleate vesicles cannot be considered proper chemical equilibrium systems, however they behave in a mixed way, with some features that are typical of micelles in equilibrium (Luisi, 2001). 

5 aqueous buffer. As for most long-chain fatty acids, there is a spontaneous vesiculation in the form of unilamellar vesicles, with a size distribution that depends on the preparation procedure - initial concentration, velocity of injection, pH, etc. -but typically with radius in the range 20-1000 nm. 

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