Thermal fluctuations of DNA enclosed by glycerol-water glassy matrices: an elastic neutron scattering investigation.

Through elastic neutron scattering measurements, we investigated the thermal fluctuations of DNA enclosed by glycerol-water glassy matrices, at different levels of hydration, over the wide temperature range from 20 to 300 K. For all the samples, the extracted hydrogen mean square displacements (MSD) show a purely vibrational harmonic trend at very low temperatures, and a first onset of anharmonic dynamics above approximately 100 K. Such onset is consistent with the activation of DNA methyl group rotational motions. Then, at a certain temperature Td, the MSD show a second onset of anharmonicity, which corresponds to the DNA dynamical transition. The Td values vary as a function of the hydration degree of the environment. The crucial role of the solvent mobility to activate the DNA thermal fluctuations is proposed, together with a preferential hydration effect of the DNA phosphate groups. Finally, a comparison between the average mobility of homologous samples of DNA and the lysozyme protein is considered.