Department of Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700106, India.
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.
J Chem Phys. 2017 Mar 28;146(12):125101. doi: 10.1063/1.4978900.
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.
深入了解氨基酸（蛋白质的组成单元）的水合作用是实现蛋白质整体溶剂化过程的关键步骤。在本研究中，我们进行了 GHz（0.2-50）至 THz（0.3-2.0）的组合实验光谱研究，以研究不同氨基酸（甘氨酸、L-丝氨酸、L-赖氨酸、L-色氨酸、L-精氨酸和 L-天冬氨酸）在室温下水中的动力学。氨基酸的 THz 吸收系数 α(ν) 遵循由其溶剂可及表面积定义的趋势。在 GHz 和 THz 区域获得的虚部和实部介电常数通过多个 Debye 模型拟合，以获得各种弛豫时间。在 GHz 频率区域获得的 ∼100 ps 时间尺度归因于氨基酸的旋转运动。在 THz 区域，我们获得了 ∼8 ps 和 ∼200 fs 的时间尺度，它们与氢键网络的协同动力学以及下配位水分子的部分旋转或突然跳跃有关。这些时间尺度取决于氨基酸的类型，协同运动既取决于氨基酸的疏水残基也取决于亲水残基。
