以oaR-TOF MS結合軟X光探討氣相Gly−Phe與Phe−Gly選擇性斷鍵的可能性以及氣膠質譜儀的設計

Abstract

本論文包含了兩個工作：第一部分是利用本實驗團隊自行建造的一套垂直加速反射式飛行時間質譜儀(oaR-TOF MS)結合同步輻射光軟X光光源可調變的光能量的特性。分析互為同分異構物(isomer)的Gly−Phe與Phe−Gly二胜肽(dipeptide)結構作為此研究的目標；以近緣X光吸收細微結構 (Near-Edge X-ray Absorption Fine Structure，NEXAFS)光譜技術提供吸收原子的電子結構並呈現靈敏的化學環境分析。隨著光能量的變化偵測到的總離子產率(total ion yield，TIY)，以各離子的訊號強度與碎片離子的branching ratio，探討Gly−Phe與Phe−Gly選擇性斷鍵(specific dissociation)的機制。並由激發碳原子的內層電子歸納出三個代表性的吸收特性，當中包含了具有芳香環的側鏈基、羰基(carbonyl group)以及Phenylalanine側鏈基碳原子的激發，其光譜特性分別為πC=C*(Cring)、πC=O*以及未飽和鍵結的碳原子混合Phenylalanine側鏈基上飽和鍵結的碳原子σ C-H*的激發。 第二個部分為氣膠(aerosol)進樣系統(intet)的設計、系統組裝與進樣源穩定所需時間的測試，並以分段抽氣系統(differential pumping system)控制偵測腔體(detection chamber)的真空度。設計此系統的目的，主要是為了解決生物分子(biomolecules)在氣化過程中產生的熱分解的現象，以及長時間曝露在高強度的同步輻射光源可能產生的輻射傷害(radiation demage)。氣膠進樣(inlet)方式是透過氣動聚焦系統(aerodynamic lens，ADL) 使氣膠粒子匯聚成束，形成一平行且發散角度極小的氣膠進樣源，結合特殊設計的加熱載台達到瞬間汽化為主要的目標。粒徑分析的實驗，顯示濃度的樣品溶液在不呈正比的情況下，氣膠微粒濃度仍具有其穩定性(至少能維持四小時以上)。

Two works are included in this thesis: The first part is to use an orthogonal acceleration reflectron time-of-flight mass spectrometer and soft X-rays from synchrotron radiation to measure near-edge X-ray absorption fine structure (NEXAFS) spectra of carbon atoms in dipeptide isomers, Gly−Phe and Phe−Gly. NEXAFS spectroscopy has been proved to provide a sensitive technique for determining the electronic structure of matter accurately and for chemical analysis. The NEXAFS spectra were recorded in the vicinity of the carbon K-edge, and the specific dissociation of Gly-Phe and Phe-Gly were explored based on the signal intensity of each product ion and the branching ratio of fragments. Three kinds of absorption properties were deduced according to the core electrons of the specific carbon atoms. They included aromatic rings, carbonyl groups and the side chain of Phenylalanine. Their assignment were πC = C* (Cring)、πC = O* and the mixing of σC-H* of the saturated bonding carbon atoms on the Phenylalanine side chain and the unsaturated bonding carbon atoms repectively. The second part is the design, assembling and sample source stability testing of the aerosol injection system. Such differential pumping plays an important role to the injection devices and the real pressures is the vacuum chambers. In differential pumping mathematics and measured results, the difference is between the values of evaluated 3.9×10-7 Torr and the 1.6×10-6 Torr of detection chamber pressure. Besides, the assembly of aerodynamic lens (ADL) to converge aerosol particles into bundles, which are instantaneously vaporized by a fast heat conduction effect occurs with a collimated particle beam. ADL also can solve the problem of thermal instability of nonvolatile biomolecules. The stability of particle size should be remained at long-term maintain. In the case of disproportionate aerosol particle concentration, it is found that the concentration of aerosol is not a factor affecting the stability. The stability of the aerosol concentration could last for more than four hours.