真空紫外光氣膠光電子能譜於氣膠及生醫科學之應用

VUV Aerosol Photoelectron Spectroscopy and Its Implications in Aerosol and Biomedical Sciences

王家蓁(Chia C. Wang)

《化學》 77卷2期 (2019/06) Pp. 165-172

https://doi.org/10.6623/chem.201906_77(2).007

摘要

光電子能譜是探測物質電子能級結構強而有力的工具。本文介紹最近開發的真空紫外光氣膠光電子能譜以及其於氣膠科學及生醫科學之應用。本文簡要敘述了此技術的實驗裝置並以三個實例呈現如何利用此技術探究胺基酸、胜肽以及苯酚類水溶液氣膠在不同酸鹼環境下的電子能級結構演變。從半胱胺酸氣膠的研究中，我們發現在不同的質子化及去質子程度下，半胱胺酸各軌域的游離能會受到其週邊化學環境的影響發生位移。當其硫醇基發生去質子化時，可能由不同的分子軌域發生游離。此一工作為親核性提供了微觀機制。從穀胱甘肽水溶液氣膠的研究中，我們藉由量測並比較穀胱甘肽與其組成之胺基酸之光電子能譜，找出胜肽的電子能級結構如何受到其組成胺基酸的影響，並揭開穀胱甘肽之所以能夠成為生物體內最強抗氧化劑的分子機理。最後，我們透過量測苯酚類水溶液氣膠之光電子能譜探討含有機溶質的氣膠之水合結構以及影響到苯酚氣膠游離能乃至後續形成次級有機氣膠的重要因子。此新穎之氣膠探測技術將可望幫助吾人對氣膠有更基礎深入且全面的認識，並藉此解決目前氣膠在環境科學、大氣科學及生醫材料科學等相關領域的重大議題。

關鍵字

氣膠 ； 真空紫外光 ； 光電子能譜 ； 水溶液氣膠 ； 半胱胺酸 ； 穀胱甘肽 ； 苯酚

並列摘要

Photoelectron spectroscopy is a powerful tool to probe the electronic energetic structures of matters. In the article, the recently developed vacuum ultraviolet (VUV) aerosol photoelectron spectroscopy and its implications in the aerosol and biomedical sciences are discussed. The experimental apparatus is first described, followed by three specific examples to demonstrate how this novel aerosol technique is capable to unravel the electronic structural evolution of amino acids, peptides and organic solute-containing aqueous aerosols. From the investigation of cysteine aqueous aerosols, we show that the band shapes and the ionization energies of different molecular orbitals vary with pH conditions, which readily reflects its corresponding chemical surrounding. Cys becomes more easily to lose an electron with increasing pH and a new ionization channel with a lower energy barrier becomes available when the thiol group is deprotonated. This work provides a microscopic perspective to explain the macroscopic concept of nucleophilicity at varying pH conditions. From the study of glutathione aqueous aerosols, the photoelectron spectra of glutathione are measured along with its three constituting amino acids, which elaborates how the electronic structures of peptides may be influenced by its constituting amino acid residues. This result provides a molecular basis to understand the molecular mechanism underlying this strongest antioxidant in biological systems. Finally, we show the photoelectron spectroscopy studies of phenol and the three isomers of dihydroxylbenzenes in the form of aqueous aerosols, from which we tackle the solvation structures of organic solute-containing aqueous aerosols and the important factors that may affect the ionization energetics of phenolic aqueous aerosols and eventually the formation of secondary organic aerosols. This article shows how this new aerosol technique can advance one's understanding of the fundamental physicochemical properties of aerosols, which sheds new lights in addressing numerous important and unresolved aerosol-related issues in the fields of environmental science, atmospheric chemistry and biomedical science.

並列關鍵字

Aerosols ； Vacuum ultraviolet ； Photoelectron spectroscopy ； Aqueous aerosols ； Cysteine ； Glutathione ； Phenol