title: Does urea alter the collective hydrogen-bond dynamics in water? A dielectric relaxation study in the terahertz-frequency region.
abstract: We report the ultrafast collective hydrogen-bond dynamics of water in the extended hydration layer of urea by using terahertz time-domain spectroscopy in the frequency region of 0.3-2.0 THz. The complex dielectric function has been fitted using a Debye relaxation model, and the timescales obtained are in the order of approximately 9 ps and 200 fs for bulk water; this exhibits a considerable acceleration beyond the 4 M urea concentration and indicates a possible disruption in the collective hydrogen-bonded water-network structure, which, in turn, provides an indirect support for the water "structure-breaking" ability of urea. With 5 M urea in the presence of different concentrations of trimethylamine-N-oxide (TMAO), it was found that these parameters essentially follow the trend observed for TMAO itself, which signifies that any possible disruption of the water structure by urea is outdone by the strong hydrogen-bonding ability of TMAO, which explains its ability to revive urea-denatured proteins to their respective native states.
authors.affiliation: Department of Chemical, Biological and Macromolecular Sciences, S.N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098 (India).
authors.forename: Nirnay
authors.initials: N
authors.lastname: Samanta
authors.forename: Debasish
authors.initials: D
authors.lastname: Das Mahanta
authors.forename: Rajib
authors.initials: R
authors.lastname: Kumar Mitra
mesh_terms: D017097:Electric Impedance; D006860:Hydrogen Bonding; D008744:Methylamines / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D055068:Terahertz Spectroscopy; D014508:Urea / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D008744:Methylamines; D014867:Water; D014508:Urea; C005855:trimethyloxamine
keywords: hydrogen bonds; solvation; time-resolved spectroscopy; urea; water chemistry