Dresden 2009 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 18: Polyelectrolytes

CPP 18.3: Talk

Tuesday, March 24, 2009, 10:00–10:15, ZEU 114

Counterion condensation on compact molecules — Ute Böhme and •Ulrich Scheler — Leibniz-Institut für Polymerforschung Dresden, Hohe Str. 6, 01069 Dresden

Condensation of counterions reduces the effective charge of macromolecules. Electrophoresis NMR provides a versatile tool for the experimental determination of the effective charge [1, 2]. The detection in both diffusion and electrophoresis NMR is performed with chemical shift resolution, enabling the identification of the moving species. Condensation of organic counterions is thus monitored directly [3]. Stiff, rod-like molecules, flexible polymers and globular molecules like proteins [4] have been investigated, proofing the concept of counterion condensation. Dendrimers are studied as model systems for nearly spherical polyelectrolytes. Inspection of the proton NMR spectra yields information on the degree of protonation of amino groups and thus the nominal charge of dendrimers. The effective charge of these small globular molecules is a fraction of their nominal charge. The effective charge does not reach the maximal nominal charge even for a small molecule like citric acid.

[1] U. Böhme, U. Scheler, Colloids and Surfaces A, 222, (2003), 35 [2] K. Grass, U. Böhme, U. Scheler, H. Cottet, C. Holm, Physical Review Letters 100, (2008) 096104 [3] U. Böhme, C. Vogel, J. Meier-Haack, Us. Scheler, J. Phys. Chem. B 111, (2007), 8344 [4] Ute Böhme, Ulrich Scheler Chemical Physics Letters 435, (2007), 342