Structural Changes of Flexible, Small-Sized Polycationic Microgels Upon Interaction With Hexacyanoferrate(III) Viewed at an Atomic and a Particle Scale

Title data

Neubert, Richard ; Schumann, Erik ; Schildknecht, Vincent ; Lehmann, Annika ; Rosenfeldt, Sabine ; Hübler, Conrad ; Plamper, Felix A.:
Structural Changes of Flexible, Small-Sized Polycationic Microgels Upon Interaction With Hexacyanoferrate(III) Viewed at an Atomic and a Particle Scale.
In: Macromolecular Chemistry and Physics. Vol. 227 (2026) . - e00493.
ISSN 1521-3935
DOI: https://doi.org/10.1002/macp.202500493

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Abstract in another language

Charged colloid systems pose challenges and offer unexpected chances in their dispersion/solution behaviour because of the interdependence of structural reorganizations, electrostatics and molecular ion binding. Here, strong polyelectrolytic P(NIPAM-co-MAPTAC) microgels/nanogels consisting of N-isopropylacrylamide (NIPAM) and [3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC, quaternized from N-(3-dimethylaminopropyl)methacrylamide, DMAPMA) with ultrasmall hydrodynamic radius (41 nm, 20°C, 0.1 m KCl; minimum: 25 nm) are prepared and investigated with varying concentrations of multivalent counterions as ionic cargo (i.e. hexacyanoferrate(III)). We combine paramagnetic relaxation enhancement NMR (PRE-NMR), dynamic light scattering DLS, and small angle X-ray scattering SAXS (fuzzy-sphere extended model) with quantum chemical calculations (r2SCAN-3c) to probe binding geometries and structural transitions across varying salt concentrations and temperatures under flooding (/nondialyzed) versus dialyzed conditions. PRE-NMR reveals selective [Fe(CN)6]3− binding to MAPTAC, assisted with secondary amide-hexacyanoferrate coordination according to quantum chemical calculations. SAXS quantifies ion-induced reorganizations: core contraction, fuzzy shell expansion, and changes in the correlation length upon hexacyanoferrate addition, accompanied by a reentrant swelling based on the preferential interaction of hexacyanoferrate with the charged microgel domains. This multiscale approach demonstrates that peripheral charge localization enables reversible switching between intra- and interparticle crosslinking, where the thermal history above 55°C can be recorded. Our results could have implications on applications like sensing, controlled release and nanoparticle-templated catalysis.