极性液体中偶极杂质的太赫兹响应：蛋白质溶液的反常介电吸收
Terahertz response of dipolar impurities in polar liquids: On anomalous dielectric absorption of protein solutions
摘要：
本文提出了介质混合物的辐射吸收理论。粗粒配方是基于主极性液体的分子偶极子的波矢依赖的关联函数和溶质的位置的密度-密度结构因子。的吸收系数对溶质浓度的非线性依赖关系的预测和起源于由沿辐射场排列的溶质偶极子的集体场的溶质周围的液体的相互极化。该理论被应用到太赫兹吸收的水合淀粉和蛋白质。虽然该理论给出了一个很好的帐户的观察没有额外的假设和拟合参数，蛋白质溶液的实验吸收系数显着超过理论计算在标准的介电模型，并显示出对蛋白质浓度的峰值。要解释标准理论与实验之间的差异，需要蛋白质水化壳的实质性极化。当从数值模拟得到的蛋白质与其水化壳的总偶极矩的关联函数用于本解析模型时，得到了与实验中所见类似的吸收峰。该结果对溶液中蛋白质-蛋白质相互作用的细节敏感。理论的数值测试需要结合太赫兹介电和小角度散射测量。
英文摘要：
A theory of radiation absorption by dielectric mixtures is presented. The coarse-grained formulation is based on the wavevector-dependent correlation functions of molecular dipoles of the host polar liquid and a density-density structure factor of the positions of the solutes. A nonlinear dependence of the absorption coefficient on the solute concentration is predicted and originates from the mutual polarization of the liquid surrounding the solutes by the collective field of the solute dipoles aligned along the radiation field. The theory is applied to terahertz absorption of hydrated saccharides and proteins. While the theory gives an excellent account of the observations for saccharides without additional assumptions and fitting parameters, experimental absorption coefficient of protein solutions significantly exceeds theoretical calculations within standard dielectric models and shows a peak against the protein concentration. A substantial polarization of protein's hydration shell is required to explain the differences between standard theories and experiment. When the correlation function of the total dipole moment of the protein with its hydration shell from numerical simulations is used in the present analytical model an absorption peak similar to that seen is experiment is obtained. The result is sensitive to the specifics of protein-protein interactions in solution. Numerical testing of the theory requires the combination of terahertz dielectric and small-angle scattering measurements.
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