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| Main Authors: | , , , , , , |
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| Format: | Preprint |
| Published: |
2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2509.24641 |
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| _version_ | 1866917224367783936 |
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| author | Sakuta, Hiroki Akamine, Yuki Kamo, Akari Gong, Hao Ichihashi, Norikazu Nikoubashman, Arash Yanagisawa, Miho |
| author_facet | Sakuta, Hiroki Akamine, Yuki Kamo, Akari Gong, Hao Ichihashi, Norikazu Nikoubashman, Arash Yanagisawa, Miho |
| contents | Mixtures of polyethylene glycol (PEG) and dextran (Dex) represent a widely used class of aqueous two-phase systems (ATPS), with applications ranging from the purification of various biomolecules such as nucleic acids to the synthesis of protocells. A key feature underlying these applications is the selective accumulation of biomolecules within Dex-rich droplets in an aqueous PEG phase, but the physical origin of this partitioning remains unclear. Entropic interactions were long assumed to be the primary driving force; however, our systematic experiments using DNA of different lengths indicate that entropy alone cannot fully explain the observed behavior. We identify an additional and previously underappreciated contribution from electrostatic interactions: Dex carries a slightly more negative charge than PEG, which drives preferential cation accumulation in the Dex-rich phase. These counterions facilitate the selective partitioning of DNA inside the Dex-rich droplets. This mechanism explains the dependency of DNA uptake in Dex-rich droplets on polymer length and salt concentration. Our findings establish that Donnan-type ion partitioning plays a crucial role in the localization of long nucleic acids in Dex-rich droplets, offering a unified explanation for this long-standing phenomenon. They lay the foundation for designing ATPS-based systems and help elucidate the physicochemical principles of biomolecular partition upon phase separation in cells. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_24641 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Cation accumulation drives the preferential partitioning of DNA in an aqueous two-phase system Sakuta, Hiroki Akamine, Yuki Kamo, Akari Gong, Hao Ichihashi, Norikazu Nikoubashman, Arash Yanagisawa, Miho Soft Condensed Matter Mixtures of polyethylene glycol (PEG) and dextran (Dex) represent a widely used class of aqueous two-phase systems (ATPS), with applications ranging from the purification of various biomolecules such as nucleic acids to the synthesis of protocells. A key feature underlying these applications is the selective accumulation of biomolecules within Dex-rich droplets in an aqueous PEG phase, but the physical origin of this partitioning remains unclear. Entropic interactions were long assumed to be the primary driving force; however, our systematic experiments using DNA of different lengths indicate that entropy alone cannot fully explain the observed behavior. We identify an additional and previously underappreciated contribution from electrostatic interactions: Dex carries a slightly more negative charge than PEG, which drives preferential cation accumulation in the Dex-rich phase. These counterions facilitate the selective partitioning of DNA inside the Dex-rich droplets. This mechanism explains the dependency of DNA uptake in Dex-rich droplets on polymer length and salt concentration. Our findings establish that Donnan-type ion partitioning plays a crucial role in the localization of long nucleic acids in Dex-rich droplets, offering a unified explanation for this long-standing phenomenon. They lay the foundation for designing ATPS-based systems and help elucidate the physicochemical principles of biomolecular partition upon phase separation in cells. |
| title | Cation accumulation drives the preferential partitioning of DNA in an aqueous two-phase system |
| topic | Soft Condensed Matter |
| url | https://arxiv.org/abs/2509.24641 |