Charge, Packing and Molecular Dynamics in Polymer Systems Studied by Magnetic Resonance

April 2, 2019

VIDEO LECTURES PART 1 OF 2:

VIDEO LECTURES PART 2 OF 2:

Professor Ulrich Scheler

The Leibniz Institute of Polymer Research Dresden

ABSTRACT

The effective charge of polyelectrolytes depends on the condensation of counterions. Counterion condensation is influenced by the ionic strength or pH of the solvent. The combination of diffusion and electrophoresis NMR permits the direct determination of the effective charge of macromolecules or complexes in solution. With knowledge of nominal charge the fraction of condensed counterions is determined. The binding between oppositely charged molecules can be followed with this approach in particular if both give an NMR signal.
From diffusion NMR the hydrodynamic size of polyelectrolytes in solution is derived via the Einstein equation. Enhanced counterion condensation resulting from higher ionic strength or other changes of the solvent leads to a more coiled conformation of the polymers. Such a coiled conformation is retained in polyelectrolyte complexes or multilayers. Solid-state NMR experiments probing proximity like double quantum or heteronuclear correlation experiments proof for such cases the presence of regions of one of the components only. These micro heterogeneities result in heterogeneous dynamic behavior. NMR provides insight to the molecular dynamics over a wide range of correlation times choosing the right type of experiment. In addition the signals are detected with spectroscopic information which permits to assign the information on the motion to individual species.
Further selective information on mobility is obtained from spin-label EPR, where a low concentration of nitroxide spin labels is attached to polyelectrolytes providing selective information on the mobility of the polyelectrolytes in multilayers or complexes.

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