Reexpansion of charged nanoparticle assemblies in concentrated electrolytes

• 成果类型: Article
• 署名作者: Reinertsen, Roger J. E.; Kewalramani, Sumit; Jimenez-Angeles, Felipe; Weigand, Steven J.; Bedzyk, Michael J.; de la Cruz, Monica Olvera
• 署名单位: Northwestern University; United States Department of Energy (DOE); Argonne National Laboratory; Northwestern University; Northwestern University; Northwestern University; Northwestern University
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-9837
• DOI: 10.1073/pnas.2316537121
• 发表日期: 2024-02-06
• 关键词: aqueous-solutions; asymmetric electrolytes; dielectric-constant; screening length; dna condensation; ion correlations; range order; transitions; hydration; precipitation

摘要

Electrostatic forces in solutions are highly relevant to a variety of fields, ranging from electrochemical energy storage to biology. However, their manifestation in concentrated electrolytes is not fully understood, as exemplified by counterintuitive observations of colloidal stability and long - ranged repulsions in molten salts. Highly charged biomolecules, such as DNA, respond sensitively to ions in dilute solutions. Here, we use non- base- pairing DNA- coated nanoparticles (DNA - NP) to analyze electrostatic interactions in concentrated salt solutions. Despite their negative charge, these conjugates form colloidal crystals in solutions of sufficient divalent cation concentration. We utilize small - angle X - ray scattering (SAXS) to study such DNA - NP assemblies across the full accessible concentration ranges of aqueous CaCl2, MgCl2, and SrCl2 solutions. SAXS shows that the crystallinity and phases of the assembled structures vary with cation type. For all tested salts, the aggregates contract with added ions at low salinities and then begin expanding above a cation- dependent threshold salt concentration. Wide - angle X - ray scattering (WAXS) reveals enhanced positional correlations between ions in the solution at high salt concentrations. Complementary molecular dynamics simulations show that these ion-ion interactions reduce the favorability of dense ion configurations within the DNA brushes below that of the bulk solution. Measurements in solutions with lowered permittivity demonstrate a simultaneous increase in ion coupling and decrease in the concentration at which aggregate expansion begins, thus confirming the connection between these phenomena. Our work demonstrates that interactions between charged objects continue to evolve considerably into the high- concentration regime, where classical theories project electrostatics to be of negligible consequence.