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Effective charge and hydrodynamic size of molecules and aggregates

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Pulsed-field gradient NMR is applied to measure displacements like flow and diffusion. From the diffusion coefficient the hydrodynamic size is determined. Sizes from 0.1 nm to 300 nm are accessible, individual species are identified by the chemical shift in the NMR signal. Electrophoretic motion generated by the in-situ application of a DC electric field during the experiment is detected by PFG NMR. From the combination of the electrophoretic mobility and the diffusion coefficient the effective charge is calculated without further assumptions. The effective charge of macromolecules is smaller than the effective charge because of condensation of counterions, it is utilized to follow the formation of complexes.

Examples

Electrophoresis NMR spectrum correlating electrophoretic mobility and chemical shift of glutamic acid (negative) and arginine (positive)
Effective charge of poly(styrene sulfonate) as a function of the dielectric constant of the solution adjusted by mixing water and methanol.
Hydrodynamic radius of poly(styrene sulfonate) as a function of the dielectric constant of the solution reflecting the change of the polymer conformation triggered by the enhanced condensation of counterions

Related publications

  • Böhme, U. ; Scheler, U.
    Counterion condensation and effective charge of poly(styrenesulfonate)
    Advances in Colloid and Interfaces Science 158 (2010) 63-67