标题： 阳离子积累驱动DNA在水相体系中的优先分配 显示英文标题

标题： Cation accumulation drives the preferential partitioning of DNA in an aqueous two-phase system

摘要： 聚乙二醇（PEG）和右旋糖酐（Dex）的混合物代表了一类广泛使用的水相双相系统（ATPS），其应用范围从各种生物分子（如核酸）的纯化到原细胞的合成。 这些应用的一个关键特征是生物分子在富含Dex的液滴中的选择性积累，但这种分配的物理起源仍不清楚。 耗竭相互作用长期以来被认为是主要驱动力；然而，我们使用不同长度的DNA进行的系统实验表明，仅靠耗竭无法完全解释观察到的行为。 我们发现了一种之前被低估的静电相互作用的额外贡献：Dex比PEG带有略微更多的负电荷，这促使反离子在富含Dex的相中优先积累。 这些反离子促进了DNA在富含Dex的液滴中的选择性分配。 这一机制解释了DNA在富含Dex的液滴中的摄取对聚合物长度和盐浓度的依赖性。 我们的研究结果确立了Donnan型离子分配作为富含Dex液滴中核酸定位的核心原理，为这一长期存在的现象提供了统一的解释。 它们为设计基于ATPS的系统奠定了基础，并有助于阐明细胞中相分离时生物分子分配的物理化学原理。 显示英文摘要

摘要： 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. Depletion interactions were long assumed to be the primary driving force; however, our systematic experiments using DNA of different lengths indicate that depletion 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 Donnan-type ion partitioning as a central principle of nucleic acid localization 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.