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Dynamics and structure of deoxyribonucleic acid salt solutions: influence of counterion valency

Double-stranded DNA functions in aqueous environment at room temperature. Strong Coulomb interactions together with parameters characterizing DNA solution (such as charge density, valency, concentration and added salt ionic strength) play an important role in determining DNA structure and tightly related biological functions. In particular, the critical role of counterion valency in modulating inter-polyion forces was comprehended only recently [1]. In the presence of univalent counterions, the dominant force between DNA polyions is like-charge repulsion, while increasing the valency of counterions induces like-charge attraction yielding the condensation into compact structures. We used dielectric spectroscopy in order to study the influence of counterion valency (monovalent sodium and divalent magnesium and manganese counterions) on the structural and dynamical properties of DNA aqueous solutions in concentration range 0.01-5 g/L. We used UV spectrophotometry, ICP-AES and electrophoresis for sample characterization. In addition, we revisited the open question of DNA conformation at low concentrations in the presence of monovalent counterions and present new results which might suggest the presence of single DNA chains instead of double-stranded conformation at the time scale of the dielectric spectroscopy measurements [2, 3, 4]. Finally, our results demonstrate that divalent magnesium and manganese cations significantly contribute to the DNA self-screening of electrostatic interactions. Their screening efficiency is anomalously large when compared to univalent sodium cation standard, which when present in small concentrations is not capable of fully preserving double strand conformation of the DNA. However, with magnesium and manganese counterions at room temperature there is as yet no net attraction between DNA segments that would be capable of inducing the full DNA collapse [5, 6]. In order to check the latter effects, we plan experiments on DNA with manganese counterions at temperatures higher than room temperatures based on the previous results by D.Rau et al. [7]. [1] A.Naji, M. Kanduč, J. Forsmann, and R. Podgornik, J.Chem.Phys.139, 150901 (2013). [2] S.Tomić, S. Dolanski Babić, T. Vuletić, S. Krča, D.Ivanković, L. Griparić i R. Podgornik, Phys. Rev. E 75, 021905 (2007). [3] K. Salamon, D.Aumiler, G.Pabst and T.Vuletić, Macromolecules 46, 1107 (2013). [4] D. Grgičin et al. in preparation (2014). [5] D. Grgičin, S. Dolanski Babić, T. Ivek and S. Tomić, Phys. Rev E 88, 052703 (2013). [6] D. Grgičin et al. in preparation (2014). [7] D. C. Rau, V. A. Parsegian, Biophys. J. 61, 246 (1992). ; D. C. Rau, V. A. Parsegian, Biophys. J. 61, 260 (1992).

dynamics of DNA; structure of DNA; counterion valency; screening

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