Dresden 2026 – scientific programme

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BP: Fachverband Biologische Physik

BP 14: Poster Session II

BP 14.93: Poster

Tuesday, March 10, 2026, 18:00–21:00, P2

Phase separation in chemically reacting systems controls cross-phase pH difference — Linge Li, •Omar Adame-Arana, and Frank Jülicher — Max Planck Institute for the Physics of Com- plex Systems, Nöthnitzer Str. 38, 01187, Dresden

Biomolecular condensates are increasingly recognized as dynamic chemical environments whose properties are strongly modulated by their pH environment. Recent experiments have focused on the pH differences between the coexisting liquid phases, but a minimal theoretical framework that can account for these observations and elucidating their physical principles is still lacking. Here, we develop a minimal thermodynamic model that integrates charge-regulated macromolecules and their counterions. By identifying the conjugate thermodynamic variables constrained by chemical equilibrium and charge neutrality, we construct the thermodynamics at equilibrium and uncover a variety of phase behaviors. We show that asymmetric partitioning of ions in phase separated compartments naturally generates electric potential and pH differences, with the dense-phase pH consistently buffered toward the macromolecular isoelectric point. We further demonstrate that these pH differences are governed by macromolecular interactions and molecular properties. Together, our results suggest that phase separation provides a robust mechanism for buffering dilute-phase pH variations and enabling controlled modulation of pH in the presence of condensates. The framework uncovers general physical principles of how pH regulation can be achieved phase-separated environments.

Keywords: Biological condensate; pH regulation; Electric potential; Flory-Huggins; Thermodynamic model