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The 2025 Professor Franz Brandstetter Prize, awarded by the Association of Supporters of the Leibniz Institute of Polymer Research Dresden (IPF), has been presented to Sascha Bartosch for his master's thesis titled “Investigation of weak binding of cationic ligands to a strong anionic polyelectrolyte studied by pulsed-field gradient NMR.”
Weak non-covalent interactions, including electrostatic forces, hydrogen bonding, and hydrophobic effects, are central to numerous biophysical processes such as signal transduction, liquid–liquid phase separation, and drug delivery. However, quantifying these interactions in solution and disentangling their individual contributions remains a significant challenge due to the lack of suitable experimental methods.
In his thesis, Bartosch investigated model systems consisting of polystyrene sulfonate, a strong anionic polyelectrolyte, and lysine, an amino acid with a pH-dependent net charge. Using pulsed-field gradient nuclear magnetic resonance (NMR) in combination with electrophoretic NMR, he was able to determine effective molecular charges and quantify binding strengths in solution. While diffusion measurements provided high-precision data on interaction effects, electrophoretic NMR offered complementary information on electrostatic contributions, enabled by an in-house-built probe head.
The results reveal a pronounced pH dependence of binding. Notably, a significant fraction of ligands remains bound even at the isoelectric point, indicating the presence of additional non-electrostatic interactions. Conversely, when both interaction partners carry charges of the same sign, binding is effectively suppressed due to electrostatic repulsion.
Overall, Bartosch’s thesis demonstrates that the combination of diffusion and electrophoretic NMR enables the analysis of weak binding interactions. The findings hold promise for pharmaceutical applications and for advancing the understanding of biomolecular condensates—structures that play a critical role in cellular organization and disease mechanisms.
Sascha Bartosch, bartosch@ipfdd.de
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