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

International audienceThrough 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 wide 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 Td = 230 – 240 K. 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 the 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

Low-frequency dynamics of water absorbed in Nafion membranes as a function of the temperature.

International audienceWe performed a neutron scattering study to investigate the dynamical behavior of water absorbed in Nafion at low hydration level (λ=6, λ = moles of water/moles of sulfonic acid sites) as a function of temperature in the range 200K-300K. To single out the signal of the confined water the measurements were done on samples hydrated with both H2O and D2O in the same temperature range. Due to the strong incoherent scattering cross section of hydrogen atoms with respect to deuterium, in the difference spectra the contribution from the Nafion membrane is subtracted out and most part of the spectra originates from absorbed water. The estimated dynamical susceptibility exhibits features that resemble those of bulk water. In particular, the spectra display a bump at around 1 meV, possibly related to α relaxation, the intensity of which is markedly affected by the temperature change. Two features due to the phonon-like collective hydrogen bond network dynamics are well visible at approximately 7 meV and 25 meV