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Fundamental Length Scales and Screening in Dilute and Semidilute Na-DNA Aqueous Solutions

Structural properties of Na-DNA dilute and semidilute aqueous solutions are quantified using dielectric spectroscopy in the frequency range 100 Hz – 100 MHz[1, 2, 3]. Two relaxation modes are revealed that can be attributed to diffusive motion of DNA counterions. The overall study in the wide concentration, added salt and chain length range demonstrates that the motion detected at lower frequencies probes single-chain structural properties, whereas the one at higher frequencies characterizes the collectives properties of the DNA solution composed of many chains. The characteristic length scales found in the measurements compare well with the fundamental length scales predicted by the theory, as well as respective roles in ionic screening of intrinsic DNA counterions and added salt ions [4]. Surprisingly, results obtained on 146 bp double-stranded DNA indicate that these short DNA fragments exhibit much higher flexibility than expected from the conventional worm-like chain model. Our results are in accord with those obtained in similar studies using small-angle X-ray scattering and fluorescence resonance energy transfer [5]. At the end, open issues and prospects for further research are designated. References [1] S.Tomic, T.Vuletic, S.Dolanski Babic, S.Krca, D.Ivankovic, L.Griparic and R.Podgornik, Phys.Rev.Lett. 97, 098303 (2006). [2] S.Tomic, S.Dolanski Babic, T.Vuletic, S.Krca, D.Ivankovic, L.Griparic and R.Podgornik, Phys.Rev.E 75, 021905 (2007). [3] S.Tomic, S.Dolanski Babic, T.Ivek, T. Vuletic, S. Krca, F.Livolant and R. Podgornik, Europhys.Letters 81, 68003 (2008). [4] A.V.Dobrynin and M.Rubinstein, Prog.Polym.Sci. 30, 1049 (2005) ; A.V.Dobrynin, R.H.Colby and M.Rubinstein, Macromolecules 28, 1859 (1995). [5] C.Yuan, H.Chen, X.W.Lou and L.A.Archer, Phys.Rev.Lett.100, 018102 (2008).

DNA dielectric relaxation; fundamental length scales; screening

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