Complex Coacervates for Polymorphism Control in Molecular Crystallization

Complex coacervation is a liquid–liquid phase separation process in which oppositely charged polyelectrolytes form a dense, polymer-rich phase that coexists in equilibrium with a dilute supernatant. This phenomenon has been related to various intracellular mechanisms due to its ability to compartmentalize, sequester, and selectively concentrate ions and biomolecules. We hypothesize that coacervates can act not only as microenvironments for molecular concentration but also as dynamic platforms that promote the crystallization of inorganic ions. Recently, we demonstrated membraneless coacervates formation as protocells for RNA evolution. Herein, we show an unprecedented level of control over crystallization of calcium oxalate (polymorphism control) in macroscopically confined coacervate environment as an excellent model for crystallization of biomolecules in living organisms, e.g. coacervates formed by poly (diallyl dimethylammonium) and poly(acrylate) effectively concentrate calcium and oxalate ions, facilitating crystallization with controlled size distribution, morphology, and polymorph selectivity. Kinetics of crystal growth was found to be strongly influenced by polymer concentration, composition, and pH. These findings highlight the potential of complex coacervates as versatile, biomimetic platforms for controlling mineralization processes with implications in both biological systems and designing new materials.