The self-assembly of oppositely charged polyelectrolytes yields different morphologies ranging from solids to liquids. In certain conditions defined, among others, by the polymer concentration and ionic strength in solution, polycation and polyanion complexation leads to liquid-like phase separated entities termed coacervates. In the latter, polymer-rich droplets suspended in a dilute surrounding have been suggested as plausible protocellular models. This work investigates the prospect of complex coacervates as protocells in an environmental scenario proposed for the early Earth: the wet-dry cycle. Periods of dehydration and rehydration have been shown to drive the formation of different types of chemical functionalities opening the door for an increase in molecular complexity. Here, experiments show that this process leads to a change in the composition of complex coacervates and, depending on the starting point, could drive the solution into a two- or one-phase system. Along the way, the partitioning of a guest molecule between the two phases is probed and its diffusion within the concentrated phase, and between the phases, is measured. While more mobility is observed as salt concentration increases, the trend in the guest polymer concentration within the coacervate is not immediately evident as it either decreases or stays constant depending on the amount added initially. This range of behaviors, seen during the drying of a single mixture, is compared to observations in different compositions mimicking those obtained throughout the dehydration process. The comparison showcases how one cycle can lead to moving through various positions on the phase diagram for a coacervate system. Further experiments explore additional compositional changes as well as the effects of multiple cycles. From a fundamental perspective, this study demonstrates the need for a better understanding of guest molecules interactions within coacervates. More broadly, it establishes a framework to examine the impact of wet-dry cycling on the structure and reactivity in non-membranous compartments.

Impact of the wet-dry cycle on polyelectrolyte complex coacervates

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.