Self-assembly of model protocell membranes*

Fatty acids, encountered commonly as soap, form micelles at pH values above their pKa and neat oil below their pKa. At a pH range about their pKa, however, they form bilayers much like the phospholipid membranes that comprise the cell membranes of life on Earth. Because of their chemical simplicity and easy self-assembly, they are of great interest as components of the membranes of potential protocells on early Earth.

We find that assembling fatty acid vesicles from micelles gives almost 100% yield of unilamellar vesicles under certain circumstances, and discuss the conditions under which unilamellar fatty acid vesicle formation is thermodynamically favoured.

We also find that creating fatty acid vesicles from neat-oil in the presence of extensive surface area features (e.g. colloidal particles, porous materials) strongly biases the population towards giant oligolamellar vesicles. This has implications for those studying the origins of life because it suggests that giant uni- and oligo-lamellar vesicles may have formed in abundance in settings where sediment and porous substrates were likely present.