  Mixtures of several macromolecular species can lead to the formation of
higher-order structures that often display non-ideal mixing behavior. In this
work, we propose a minimal model of a quaternary system which considers the
formation of a complex via a chemical reaction involving two macromolecular
species; the complex may then phase separate from the buffer and undergo a
further transition into a gel-like state over time. First, a ternary phase
diagram that captures the volume fraction of each species and phases at
equilibrium is constructed. Specifically, we investigate how physical
parameters such as stoichiometric coefficients, molecular sizes and interaction
parameters affect LLPS and aging. Finally, we analyze the thermodynamic
stability of the two-phase system and identify the spinodal regions, and
outline the generalization of our approach to reactive biomolecular systems
with an arbitrary number of components.
