Broadband Dielectric Spectroscopy on Lysozyme in the Sub-Gigahertz to Terahertz Frequency Regions: Effects of Hydration and Thermal Excitation
Broadband Dielectric Spectroscopy on Lysozyme in the Sub-Gigahertz to Terahertz Frequency Regions: Effects of Hydration and Thermal Excitation
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DOI：
10.1021/acs.jpcb.6b01491
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发表时间：
2016-06-02
影响因子：
3.3
通讯作者：
Tominaga, Keisuke
中科院分区：
文献类型：
--
作者：
Yamamoto, Naoki;Ohta, Kaoru;Tominaga, Keisuke
我们已经进行了介电光谱测量的溶菌酶在固体状态下，以了解水合和热激发的影响的低频动力学的蛋白质。在室温下，在0.5 GHz至1.8 THz的频率范围内，在不断变化的水合条件下进行介电测量。我们还研究了在太赫兹频率范围内（0.3太赫兹至1.8太赫兹）的复介电谱的温度依赖性（83至293 K）。使用模型函数的复介电常数进行光谱分析。为了重现光谱，我们发现，两个弛豫模式和两个欠阻尼模式是必要的，连同在模型函数中的离子电导率项。在室温下，这两种弛豫模式的弛豫时间分别为20 ps和100 ps。更快的组件有一个主要的光谱强度，并建议是由于耦合水蛋白质运动。这两个欠阻尼模式是必要的，在太赫兹区域满意地再现光谱的温度依赖性。蛋白质动力学转变是蛋白质的中子散射实验中的一个众所周知的行为，其中当样品水合时，原子均方位移在约200 K处显示出温度依赖性的突然变化。蛋白质在太赫兹波段的吸收光谱随温度的变化也表现出类似的行为。从我们的宽带介电光谱测量，我们得出结论，在太赫兹区域在约200 K的光谱强度的增加是由于快速弛豫模式的光谱蓝移。
We have performed dielectric spectral measurements of lysozyme in a solid state to understand the effects of hydration and thermal excitation on the low-frequency dynamics of protein. Dielectric measurements were performed under changing hydration conditions at room temperature in the frequency region of 0.5 GHz to 1.8 THz. We also studied the temperature dependence (83 to 293 K) of the complex dielectric spectra in the THz frequency region (0.3 THz to 1.8 THz). Spectral analyses were performed using model functions for the complex dielectric constant. To reproduce the spectra, we found that two relaxational modes and two underdamped modes are necessary together with an ionic conductivity term in the model function. At room temperature, the two relaxational modes have relaxation times of similar to 20 ps and similar to 100 ps. The faster component has a major spectral intensity and is suggested to be due to coupled water-protein motion. The two underdamped modes are necessary to reproduce the temperature dependence of the spectra in the THz region satisfactorily. The protein dynamical transition is a well-known behavior in the neutron-scattering experiment for proteins, where the atomic mean-square displacement shows a sudden change in the temperature dependence at approximately 200 K, when the samples are hydrated. A similar behavior has also been observed in the temperature dependence of the absorption spectra of protein in the THz frequency region. From our broadband dielectric spectroscopic measurements, we conclude that the increase in the spectral intensities in the THz region at approximately 200 K is due to a spectral blue-shift of the fast relaxational mode.