title: Collective hydration dynamics in some amino acid solutions: A combined GHz-THz spectroscopic study.
abstract: A detailed understanding of hydration of amino acids, the building units of protein, is a key step to realize the overall solvation processes in proteins. In the present contribution, we have made a combined GHz (0.2-50) to THz (0.3-2.0) experimental spectroscopic study to investigate the dynamics of water at room temperature in the presence of different amino acids (glycine, L-serine, L-lysine, L-tryptophan, L-arginine, and L-aspartic acid). The THz absorption coefficient, α(ν), of amino acids follows a trend defined by their solvent accessible surface area. The imaginary and real dielectric constants obtained in GHz and THz regions are fitted into multiple Debye model to obtain various relaxation times. The ∼100 ps time scale obtained in the GHz frequency region is attributed to the rotational motion of the amino acids. In the THz region, we obtain ∼8 ps and ∼200 fs time scales which are related to the cooperative dynamics of H-bond network and partial rotation or sudden jump of the under-coordinated water molecules. These time scales are found to be dependent on the amino acid type and the cooperative motion is found to be dependent on both the hydrophobic as well as the hydrophilic residue of amino acids.
authors.affiliation: Department of Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700106, India.
authors.forename: Nirnay
authors.initials: N
authors.lastname: Samanta
authors.affiliation: Department of Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700106, India.
authors.forename: Debasish
authors.initials: D
authors.lastname: Das Mahanta
authors.affiliation: Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700106, India.
authors.forename: Samiran
authors.initials: S
authors.lastname: Choudhury
authors.affiliation: Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700106, India.
authors.forename: Anjan
authors.initials: A
authors.lastname: Barman
authors.affiliation: Department of Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700106, India.
authors.forename: Rajib
authors.initials: R
authors.lastname: Kumar Mitra
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D058266:Dielectric Spectroscopy; D057927:Hydrophobic and Hydrophilic Interactions; D012996:Solutions; D055068:Terahertz Spectroscopy; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D000596:Amino Acids; D012996:Solutions; D014867:Water