we added a new footnote, to explain our standing on this issue: Reference 36: In this work, concentrations outside the vesicle are set as system parameters. However, we make no commitment to the type of environment the vesicle is embedded in or how these concentrations are maintained. Our purpose is simply to show that bistability can exist in the model for certain sets of outside concentrations. Exploration of the model in explicit environments is deferred to future work.
Remarkably, even reaction systems that have no chemical species in common could become R2 indirectly coupled to each other through the volume they share, by means of a sort of osmotic coupling.