胜肽模型分子的選擇性斷鍵與胜肽的結構分析預測

我們建造了一套垂直加速飛行時間質譜，希望能使用質譜的技術來了解類生物分子在吸收軟X光、內層電子被激發後，進行分解、找到選擇性分解的特性，並藉此來幫忙預測生物分子在相似情形下的分解情形。這套質譜儀配合國家同步輻射中心的軟X光化學光束線一起建造，所以可以輕易改變X光光子的能量，並進而使用總離子產量的方式來量測研究分子的吸收光譜，此篇文章中介紹了將肽模型加入了苯環的兩個分子的研究，藉由同位素的結果幫助我們推論出哪一些分解方式是此分子共振吸收後進行選擇性分解的結果，我們發現在大約16-34%是肽鍵斷鍵，相比於沒有苯環的肽模型分子來說，大約只剩一半左右，主因應該電子被激發上去的電子軌域，分佈在苯環和肽鍵上，所以苯環的開環反應也是主要的反應途徑之一。另一方面，也有幾個包含兩個或三個肽鍵的肽模型分子的研究也已完成，我們發現每一個肽鍵都是選擇性斷鍵可能發生反應的位置，而且，有肽鍵斷鍵而來的產物，佔了總產物的42-75%，這是很高的比例，主因應該是電子被激發至在肽鍵上有反鍵結特性的電子軌域後所產生的化學反應。

關鍵字

垂直加速飛行時間質譜；肽模型；同步輻射；選擇性分解；肽鍵斷鍵

並列摘要

We built an orthogonal acceleration time-of-flight mass spectrometer (OA-TOF-MS) to study the dissociation of bio-like molecules following the absorption of one X-ray photon to excite a core level electron. This will help estimate how the bio-molecules dissociate under similar conditions. This mass spectrometer was built up along the Soft X-ray Beamline at NSRRC. By changing the photon energy of X-ray, the total-ion-yield near edge X-ray absorption fine structure spectra can be measured for the studied molecules. In this article, there are two peptide model molecules composed of phenyl ring of study. Using the mass spectra of the dissociated isotope substituted molecules, we have proven that the ionic products form specific dissociation following resonant excitations. The branching ratio of the products from breaking the peptide bond is about 16-34% which is N-methylformamide's half because the destination orbital includes both the phenyl ring and peptide bond. On the other hand, several peptide model molecules composed of two or three peptide bonds were also investigated. After core level resonant excitation, every peptide bond is at the location for specific dissociation to occur. The branching ratio of the ionic products formed from breaking one or more peptide bonds has a very high percentage of 42-75%. We propose that it is due to the core electron was excited to the orbitals containing the anti-bonding properties along the peptide bonds before the specific dissociation.

並列關鍵字

Orthogonal acceleration time-of-flight mass spectrometer ； OA-TOF-MS ； Peptide model ； Synchrotron radiation ； Specific dissociation ； Breaking bond

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