Regensburg 2013 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 33: Poster: Charged Soft Matter

CPP 33.8: Poster

Wednesday, March 13, 2013, 16:30–18:30, Poster C

Manning condensation on DNA fragments with monovalent and divalent counterions — •Damir Vurnek^1,2, Marija Sorić², and Tomislav Vuletić² — ¹Institut für Theoretische Physik and Cluster of Excellence: EAM, Universität Erlangen-Nürnberg, Erlangen, Germany — ²Institut za fiziku, Zagreb, Croatia

We obtained the Manning free (uncondensed) counterions fraction θ for dilute aqueous solutions of rodlike polyions: 150 bp DNA fragments, across a range of concentrations, c(monomer) = 0.03 − 8 mM. Conductometric measurements were done on Na⁺DNA and Mg⁺⁺DNA, in 1mM added salt (NaCl and MgCl₂, respectively) as well as in pure water conditions.

We remind that the high linear charge of polyions Manning condenses a fraction of counterions close to the polyion. This partly neutralizes polyion charge, and reduces the effective solution conductivity. Our conductivity study of DNA in added salt confirms theoretical values θ=0.24 and 0.12 for Na⁺DNA and Mg⁺⁺DNA, respectively. However, in pure water conditions, towards lower DNA concentrations the effective θ increases well above the Manning values. UV-absorbance measurements showed that this is not due to DNA denaturation. Denaturation may occur in pure water conditions due to a reduction in the electrostatic screening; as single stranded DNA has a lower linear charge it also has a correspondingly higher θ fraction. We concluded that in dilute solutions more counterions must become decondensed as the entropy gain overcomes the electrostatic cost, as Deshkovski et al. (Phys.Rev.Lett. 2001) indeed have discussed.