[Solubility and phase transitions in the water-protein-salt system]

Area of Science:

• Physical chemistry
• Biochemistry
• Materials science

Context:

• Phase transitions in water-protein-salt systems are crucial for understanding protein solubility and behavior.
• Existing formulas describe sol-gel, liquid-liquid, and liquid-solid transitions based on critical molar composition.
• These transitions are influenced by protein charge (z), adsorbed ion number (v), and electrolyte activity (A).

Purpose:

• To present derived formulas for phase transition curves in a graphical format (protein solubility vs. salt concentration).
• To analyze how variations in v, z, and the v/z ratio affect the phase transition lines.
• To explore the relationship between salting-out phenomena and these phase transitions.

Summary:

• Previously derived formulas for sol-gel, liquid-liquid, and liquid-solid phase transitions in water-protein-salt systems are visualized as curves of protein solubility (logS) versus salt concentration (m3).
• The study identifies tendencies in how phase transition lines shift in response to changes in ion adsorption (v), protein charge (z), and their ratio (v/z).
• The correlation between the salting-out curve, salting-out coefficient, and the observed phase transitions is discussed.

Impact:

• Provides a visual and quantitative understanding of phase behavior in protein-salt solutions.
• Offers insights into controlling protein solubility through manipulation of salt concentration and protein/ion characteristics.
• Contributes to the fundamental knowledge of protein phase diagrams and salting-out effects.