The low-frequency (1–200 cm−1) vibrational spectra of peptides and proteins in solution have been investigated with ultrafast optical heterodyne-detected Raman-induced Kerr-effect spectroscopy (OHD-RIKES). Spectra have been obtained for di-L-alanine (ALA(2)) and the α-helical peptide poly-L-alanine (PLA) in dichloroacetic acid solution. The poly-L-alanine spectrum shows extra amplitude compared to the di-L-alanine spectrum, which can be explained by the secondary structure of the former. The globular proteins lysozyme, α-lactalbumin, pepsin, and β-lactoglobulin in aqueous solution have been studied to determine the possible influence of secondary or tertiary structure on the low-frequency spectra. The spectra of the globular proteins have been analyzed in terms of three nondiffusive Brownian oscillators. The lowest frequency oscillator corresponds to the so-called Boson peak observed in inelastic neutron scattering (INS). The remaining two oscillators are not observed in inelastic neutron scattering, do therefore not involve significant motion of hydrogen atoms, and may be associated with delocalized backbone torsions.
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机译：用超快光学外差检测拉曼诱导的克尔效应光谱（OHD-RIKES）研究了溶液中肽和蛋白质的低频振动光谱（1-200 cm -1 ）。已获得二氯乙酸溶液中二-L-丙氨酸（ALA（2））和α-螺旋肽聚-L-丙氨酸（PLA）的光谱。与二-L-丙氨酸光谱相比，聚-L-丙氨酸光谱显示出额外的振幅，这可以由前者的二级结构来解释。研究了球形蛋白溶菌酶，α-乳白蛋白，胃蛋白酶和β-乳球蛋白在水溶液中的含量，以确定二级或三级结构对低频光谱的可能影响。球状蛋白的光谱已根据三种非扩散布朗振荡器进行了分析。最低频率的振荡器对应于在非弹性中子散射（INS）中观察到的所谓的玻色子峰。在非弹性中子散射中未观察到其余的两个振荡器，因此不涉及氢原子的显着运动，并且可能与离域的主干扭转相关。
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