Prebiotically relevant mixed fatty acidvesicles support anionic solute encapsulation and photochemically catalyzed trans-membrane charge transport

Abstract

The spontaneous assembly of amphiphile-based compartments in aqueous solution is widely viewed as a key step in models for the abiotic formation of primitive cell-like structures. Proposed organic components for such systems consist of mixed short chain fatty acids (FA) and polycyclic aromatic hydrocarbon (PAH) species, the composition of which have been modeled after organic extracts of carbonaceous meteorites. Self-assembly of amphiphiles from these extracts into aqueous suspensions of bilayer structures was long ago demonstrated, although little has since been reported concerning the stability and potential functionality of these complex mixtures. This work explores the thermodynamic and kinetic stability of vesicles prepared from complex mixtures of short chain FA species (CH₃COOH–C₉H₁₉COOH) with membrane solubilized PAH species. Critical vesicle concentration measurements and ultrafiltration analyses of decanoic acid in the presence of other shorter chain FA species indicate the formation of mixed component vesicle phases composed mainly of C₁₀–C₈ FA components. An electrostatic barrier to trans-membrane diffusion of negative charges allows observation of stably encapsulated poly-anionic solutes inside these vesicles. As a model for primitive energy transduction, trans-membrane electron transfer between EDTA and encapsulated ferricyanide was demonstrated, driven catalytically via PAH photochemistry without substantial decomposition of the chromophores or vesicles. These results indicate a plausible role for compartmentalization and catalysis by short chain fatty acids and PAH species in prebiotic vesicle-encapsulated systems.