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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >IR spectroscopy of b_4 fragment ions of protonated pentapeptides in the X-H (X = C, N, O) region
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IR spectroscopy of b_4 fragment ions of protonated pentapeptides in the X-H (X = C, N, O) region

机译：X-H（X = C，N，O）区域质子化五肽b_4碎片离子的红外光谱

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摘要

The structure of peptide fragments was studied using "action" IR spectroscopy. We report on room temperature IR spectra of b_4 fragments of protonated GGGGG, AAAAA, and YGGFL in the X-H (X = C, N, O) stretching region. Experiments were performed with a tandem mass spectrometer combined with a table top tunable laser, and the multiple photon absorption process was assisted using an auxiliary high-power CO_2 laser. These experiments provided well-resolved spectra with relatively narrow peaks in the X-H (X = C, N, O) stretching region for the b_4 fragments of protonated GGGGG, AAAAA, and YGGFL. The 3200-3700 cm~(-1) range of the first two of these spectra are rather similar, and the corresponding peaks can be assigned on the basis of the classical b ion structure that has a linear backbone terminated by the oxazolone ring at the C-terminus and ionizing proton residing on the oxazolone ring nitrogen. The spectrum of the b_4 of YGGFL, on the other hand, is different from the two others and is characterized by a band observed near 3238 cm~(-1). Similar band positions have recently been reported for one of the four isomers of the b_4 of YGGFL studied using double resonance IR/UV technique. As proposed in this study, the IR spectrum of this ion at room temperature can also be assigned to a linear N-terminal amine protonated oxazolone structure. However, an alternative assignment could be proposed because our room temperature IR spectrum of the b_4 of YGGFL nicely matches with the predicted IR absorption spectrum of a macrocyclic structure. Because not all experimental IR features are unambiguously assigned on the basis of the available literature structures, further theoretical studies will be required to fully exploit the benefits offered by IR spectroscopy in the X-H (X = C, N, O) stretching region.
机译：使用“作用” IR光谱法研究了肽片段的结构。我们报告质子化的GGGGG，AAAA和YGGFL在X-H（X = C，N，O）拉伸区域中b_4片段的室温红外光谱。使用串联质谱仪和台式可调谐激光器进行实验，并使用辅助大功率CO_2激光器辅助多光子吸收过程。这些实验提供了良好解析的光谱，在质子化的GGGGG，AAAAA和YGGFL的b_4片段的X-H（X = C，N，O）拉伸区域中具有相对较窄的峰。这些光谱的前两个光谱在3200-3700 cm〜（-1）范围内非常相似，并且可以基于经典的b离子结构分配相应的峰，该结构具有一个线性骨架，该骨架由恶唑酮环终止。 C-端和电离质子驻留在恶唑酮环氮上。另一方面，YGGFL的b_4光谱不同于其他两个光谱，其特征是在3238 cm〜（-1）附近观察到一个能带。最近报道了使用双共振IR / UV技术研究的YGGFL的b_4的四个异构体之一的相似的带位置。如本研究中所提议的，该离子在室温下的红外光谱也可归因于线性N端胺质子化的恶唑酮结构。但是，由于我们的YGGFL的b_4的室温IR光谱与大环结构的预测IR吸收光谱很好地匹配，因此可以提出替代方案。由于并非根据可用的文献结构明确分配所有实验性红外特征，因此需要进一步的理论研究，以充分利用X-H（X = C，N，O）拉伸区域中红外光谱的优势。

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