Structural identification of gas-phase biomolecules using infrared spectroscopy
Structural identification of gas-phase biomolecules using infrared spectroscopy
复制标题
使用红外光谱法识别气相生物分子的结构
DOI：
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发表时间：
2004
期刊：
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通讯作者：
J. Bakker
中科院分区：
文献类型：
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作者：
J. Bakker
弱的分子内和分子间相互作用以及微妙的电子效应可以对分子结构产生很大的影响。红外（IR）光谱可以成为研究这些效应的有用工具。本论文利用自由电子激光器FELIX对几种分子模型体系进行了紫外-红外双共振研究。目的是比较实验光谱与量子化学方法的结果，以获得所研究物种的信息。这是否会成功取决于两个简单问题的答案：实验是否足够好？理论足够好吗？在气相生物分子的实验中，一个关键问题是在中红外波长范围内是否可以观察到柔性分子的构象差异。根据本文所述的工作，可以肯定地回答这个问题。在研究的所有系统中，观察到可辨别的IR光谱结构，其足够尖锐以能够区分各种构象。具体而言，在一个单一的氨基酸的三种不同的构象进行了研究的情况下，它令人信服地证明，光谱技术是足够的，用于此目的。在所有其他情况下，对生物分子单一构象的研究已经产生了足够特征的光谱数据，这些数据可以导致明确的归属，或者至少可以为特定类别的构象提供强有力的证据。第二个问题是这里使用的标准理论方法是否足够准确，以允许光谱数据进行有意义的评估。必须得出结论，目前的理论对某些类型的振动是非常准确的，但对其他类型的振动就不那么准确了。对于高频拉伸振动和其他强烈局部化的弯曲和变形振动，理论方法是足够的。对于大多数低频、离域和耦合振动，可能会出现问题。
Weak intra- and intermolecular interactions as well as subtle electronic effects can have a large influence on molecular structure. Infrared (IR) spectroscopy can be a useful tool to investigate these effects. In this thesis, the Free-Electron Laser FELIX is used to study several molecular model systems using UV-IR double-resonance techniques. The aim is to compare the experimental spectra with results from quantum chemical methods to obtain information on the species studied. Whether this will be of success depends on the answer to two simple questions: Is the experiment good enough? and Is theory good enough? In the experiments on gas-phase biomolecules, a key question is whether conformational differences in flexible molecules can actually be observed in the mid-IR wavelength range. Based on the work presented here, this question can be answered positively. In all systems studied, well-discernible IR spectral structure is observed that is sharp enough to be able to differentiate between various conformers. Specifically, in the case where three different conformers of a single amino acid are investigated, it is convincingly demonstrated that the spectroscopic techniques are adequate for this purpose. In all other cases, the investigation of single conformers of biomolecules has led to spectroscopic data that are sufficiently characteristic that they could either lead to unambiguous assignments or, at least, to strong evidence for specific classes of conformations. The second question is whether the standard theoretical methods used here are sufficiently accurate to allow for the spectroscopic data to be evaluated meaningfully. It must be concluded that present theory can be very accurate for certain types of vibrations, but less so for others. For high-frequency stretching vibrations and other strongly localized bending and deformation vibrations, the theoretical methods are adequate. For, mostly low-frequency, de-localized and coupled vibrations, problems can arise.