Temperature dependence of fast fluctuations in single- and double-stranded DNA molecules: a neutron scattering investigation

Using elastic neutron scattering measurements we have investigated the picosecond dynamics of dry and hydrated powders of DNA in the double-stranded (dsDNA) and single-stranded (ssDNA) state in the temperature range from 20 to 300 K. The extracted mean square displacements of DNA hydrogen atoms exhibit an onset of anharmonicity at around 100 K. The dynamics of the hydrated samples shows a further anharmonic contribution appearing at a temperature T-d=230-240K. Such dynamical behaviour is similar to the well-studied dynamical transition found in hydrated protein powders. The mean square displacements of dsDNA and ssDNA are practically superimposed in tile whole temperature range for both dry and hydrated samples. This suggests that the DNA local mobility in the picosecond timescale does not depend on the single- or double-stranded conformation.