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bioRxiv · 10.64898/2026.06.12.731829

A minimal thermodynamic theory for re-entrant liquid-liquid phase separation regulated by small molecules

Jadhav, A.·Ghosh, P.
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Abstract

Small molecules regulate biomolecular condensates in a biphasic manner, promoting liquid-liquid phase separation (LLPS) at low concentrations while suppressing it at higher concentrations. Despite increasing experimental evidence for such re-entrant behavior, a unified physical description remains lacking. Here, we identify a minimal thermodynamic mechanism for re-entrant LLPS by coupling Cahn-Hilliard dynamics to a concentration-dependent Flory interaction parameter containing competing LLPS-promoting and inhibitory contributions. The resulting model reproduces experimentally observed nonmonotonic condensate formation in Tau-tannic acid and TDP-43-bis-ANS systems, including the concentration-dependent emergence and dissolution of protein-rich domains. Spinodal analysis reveals finite concentration windows for phase instability and demonstrates that re-entrant mixing is encoded directly in the free-energy landscape. The framework further captures morphology transitions and diffusive coarsening within the phase-separated regime. These results establish a general mesoscale description of chemically regulated condensates and provide design principles for controlling phase separation through small-molecule modulators.

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Jadhav, A., Ghosh, P.. 2026-06-16. A minimal thermodynamic theory for re-entrant liquid-liquid phase separation regulated by small molecules. https://doi.org/10.64898/2026.06.12.731829

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