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Cation Accumulation Drives the Preferential Partitioning of DNA in an Aqueous Two-Phase System
Hiroki Sakuta1,2, Yuki Akamine1, Akari Kamo3
1Komaba Institute for Science, Graduate School of Arts and Sciences, The University of Tokyo, Komaba 3-8-1, Meguro, Tokyo 153-8902, Japan.
ACS Macro Letters
|January 13, 2026
Summary
Aqueous two-phase systems (ATPS) made of polyethylene glycol (PEG) and dextran (Dex) partition biomolecules via electrostatic interactions, not just entropy. This finding clarifies DNA partitioning in Dex-rich droplets and aids ATPS design.
Area of Science:
- Biochemistry
- Physical Chemistry
- Materials Science
Background:
- Aqueous two-phase systems (ATPS) composed of polyethylene glycol (PEG) and dextran (Dex) are vital for biomolecule purification and protocell synthesis.
- Selective partitioning of biomolecules, particularly nucleic acids, into Dex-rich droplets within PEG phases is a key ATPS feature, but its physical basis is poorly understood.
- Previous explanations relied primarily on entropic forces, which failed to fully account for observed partitioning behaviors.
Purpose of the Study:
- To investigate the physical mechanisms driving the selective partitioning of DNA within Dex-rich droplets in PEG/Dex ATPS.
- To determine if entropic interactions alone can explain the observed DNA partitioning.
- To identify and characterize additional forces influencing biomolecule localization in ATPS.
Main Methods:
- Systematic experimental studies using DNA of varying lengths.
- Analysis of partitioning behavior under different salt concentrations.
- Investigation of electrostatic interactions between PEG, Dex, and counterions.
Main Results:
- Entropic interactions alone do not fully explain the observed DNA partitioning in PEG/Dex ATPS.
- Electrostatic interactions play a significant, previously underappreciated role.
- Dextran's higher negative charge density leads to preferential cation accumulation in Dex-rich phases, facilitating DNA partitioning.
- DNA partitioning is dependent on DNA length and salt concentration, consistent with a Donnan-type ion partitioning mechanism.
Conclusions:
- Donnan-type ion partitioning is a crucial factor in the localization of long nucleic acids within Dex-rich ATPS droplets.
- This electrostatic mechanism provides a unified explanation for DNA partitioning phenomena in PEG/Dex systems.
- The findings are foundational for designing advanced ATPS and understanding biomolecular partitioning during cellular phase separation.
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