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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Frequency Selected Ultrafast Infrared Vibrational Echo Studies of Liquids, Glasses, and Proteins
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Frequency Selected Ultrafast Infrared Vibrational Echo Studies of Liquids, Glasses, and Proteins

机译：频率选择的液体，玻璃和蛋白质的超快红外振动回波研究

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Ultrafast infrared frequency selected vibrational echo (FSVE) experiments are used to study temperature-dependent dynamic interactions in liquids, glasses, and proteins. Vibrational echo experiments measure vibrational dephasing. In general, the large bandwidths associated with ultrashort IR pulses will excite multiple vibrational transitions of a molecular system. In addition to the 0-1 transition of a particular mode of interest, the 1-2 transition, other modes, combination bands, and modes of other species can be excited. A one-dimensional vibrational echo experiment involving multiple transitions can be difficult to address theoretically. By selecting the proper detection wavelengths (a frequency slice through a 2D time-frequency vibrational echo), FSVE makes it possible to effectively isolate a two state system (in terms of the dynamical experimental observables) from within a complex multistate system. First, the FSVE method is used to study the dynamics of CO stretching mode of RuTPPCOPy (TPP = 5,10,15,20-tetraphenylporphyrin, Py = pyridine) in two solvents: poly(methyl methacrylate) (PMMA) and 2-methyltetrahydrofuran (2-MTHF). The results demonstrate the fundamental difference in the influence of a glassy and a liquid solvent on vibrational dephasing. In PMMA, a glass at all temperatures studied, the dephasing rate is linear in temperature. In 2-MTHF, the dephasing is linear for temperatures below T_g, but it changes form, becoming very steep slightly above T_g. Calculations using a model frequency-frequency correlation function (FFCF) show that the different temperature dependences in PMMA and 2-MTHF can be modeled in a unified manner, with at least two solvent motions contributing to the dephasing in liquids, that is, inertial and diffusive motions. FSVE is then applied to the study of the dynamics of the protein myolglobin in water by observing the vibrational dephasing of the stretching mode of CO bound o the active site of myoglobin (Mb-CO). The A_1 and A_3 conformational substates of Mb-CO are found to have different dephasing rates with different temperature dependences. A frequency-frequency correlation function derived from molecular dynamics simulations of Mb-CO at 298 K is used to calculate the vibrational echo decay. The calculated decay shows substantial agreement with the experimentally measured decays. The FSVE experiment probes protein dynamics and provides an observable that can be used to test structural assignments for the Mb-CO conformational substates.
机译：超快红外频率选择振动回波（FSVE）实验用于研究液体，玻璃和蛋白质中与温度相关的动态相互作用。振动回波实验可测量振动相移。通常，与超短IR脉冲相关的大带宽将激发分子系统的多次振动跃迁。除了特定感兴趣模式的0-1过渡之外，还可以激发1-2过渡，其他模式，组合谱带和其他物种的模式。从理论上讲，涉及多个跃迁的一维振动回波实验可能很难解决。通过选择适当的检测波长（通过2D时频振动回波的频率切片），FSVE可以有效地从复杂的多态系统中隔离出两种状态的系统（就动态实验观察而言）。首先，使用FSVE方法研究RuTPPCOPy（TPP = 5,10,15,20-四苯基卟啉，Py =吡啶）在两种溶剂（聚甲基丙烯酸甲酯（PMMA）和2-甲基四氢呋喃）中的CO拉伸模式的动力学。 （2-MTHF）。结果表明，玻璃态和液态溶剂对振动相移的影响存在根本差异。在研究了所有温度的玻璃PMMA中，相移速度在温度上都是线性的。在2-MTHF中，当温度低于T_g时，相移是线性的，但是它会改变形式，在T_g之上略微变陡。使用模型频率-频率相关函数（FFCF）进行的计算表明，可以以统一的方式对PMMA和2-MTHF中不同的温度依赖性进行建模，其中至少有两个溶剂运动有助于液体中的相移，即惯性和扩散运动。 FSVE然后通过观察结合在肌红蛋白活性位点（Mb-CO）上的CO的拉伸模式的振动相移，将FSVE应用于水中蛋白质肌红蛋白的动力学研究。发现Mb-CO的A_1和A_3构象亚状态具有不同的相移速率，并且具有不同的温度依赖性。从298 K的Mb-CO分子动力学模拟得出的频率-频率相关函数用于计算振动回波衰减。计算得出的衰减与实验测量的衰减基本吻合。 FSVE实验探查蛋白质动力学，并提供可观察的结果，可用于测试Mb-CO构象亚状态的结构分配。

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