Regensburg 2010 – wissenschaftliches Programm

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BP: Fachverband Biologische Physik

BP 38: Focus: Charge Effects in Soft and Biological Matter III (joint CPP, BP, ST)

BP 38.2: Vortrag

Freitag, 26. März 2010, 10:45–11:00, H45

Counterion condensation and effective charge of linear and globular macromolecules — Ute Böhme and •Ulrich Scheler — Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, 01069 Dresden

The charge density on charged macromolecules is usually so high, that the thermal energy of the respective counterions is insufficient to escape the electric field generated from the charges on the macromolecule. Therefore a fraction of counterions condenses on the macromolecule, lowering the effective charge of the macromolecule The combination of diffusion and electrophoresis NMR provides an umambiquous possibility for the experimental determination of the effective charge, which is in good agreement with molecular simulations [1, 2]. This approach has been applied to flexible and stiff polyelectrolytes as well as proteins and other globular molecules [5]. Because PAMAM dendrimers exhibit only two types of chargeable groups, counterion condensation can easily be quantified, where the degree of protonation of the amino groups is inferred from proton NMR spectra. The fraction of condensed counterions increases with increasing molecular weight to level at about 70%. The effect of the variation of the solvent properties is studied with variation of the ionic strength and the dielectric constant of the solution.

[1] K. Grass, U. Böhme, U. Scheler, H. Cottet, C. Holm, Physical Review Letters 100, (2008) 096104 [2] U. Scheler, Current opinion in Colloid & Interface Science, 14 (2009), 212 [3] U. Böhme, U.Scheler, Coll. & Surf.A,, 222, (2003), 35