Spatio-temporal analysis of water molecules around DNA employing extended MHz-THz spectroscopy and MD simulations*

The molecular motion of water molecules within hydration shells around DNA strongly influences its functionality. However, the structure and dynamics of water molecules in their hydration shells are still controversially discussed among the research community. The understanding developed in this regard so far, is mostly due to computational/simulation studies, with far lesser experimental investigations. Here we present a temperature-dependent study for dynamics of water molecules around salmon testes DNA, employing extended megahertz-terahertz dielectric spectroscopic technique and Fourier transform infrared spectroscopy supported by MD simulations. We have observed that water molecules are heterogeneously distributed around DNA and they can be classified as “tightly” and “loosely” bound water molecules with the relaxation times of ~500 ps and ~70 ps, respectively. We are able to locate the successive hydration layers with respect to the DNA molecule. FTIR analysis of hydrogen bond fluctuations indicates that the DNA behaves like a “chaotropic” solute and reduces the structural order of water molecules with respect to the bulk water.