Application of chemical graph theory to PAH isomer enumeration and structure in laser desorption/ionization mass spectrometry studies of particulate from an ethylene diffusion flame
Application of chemical graph theory to PAH isomer enumeration and structure in laser desorption/ionization mass spectrometry studies of particulate from an ethylene diffusion flame
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DOI：
10.1016/j.proci.2020.06.080
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发表时间：
2020-09
期刊：
影响因子：
4
通讯作者：
J. H. Miller;R. J. Golden;J. Giaccai;A. Kamischke;Andrew R. Korte;A. Vertes
中科院分区：
文献类型：
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作者：
J. H. Miller;R. J. Golden;J. Giaccai;A. Kamischke;Andrew R. Korte;A. Vertes
我们的实验室最近发表的数据表明，烟尘中的PAH成分可以通过低通量激光解吸电离结合高分辨率质谱成像来精确测定和空间分辨[1]。该分析表明，多环芳烃的239-838 Da，含有少量的含氧物质，包括在乙烯扩散火焰中观察到的烟灰。在本文中，我们表明，经验公式的观察物种可以帮助枚举的异构体和地方限制其结构和热力学稳定性。具体而言，化学图论（CGT）表明，在采样的颗粒物中观察到的绝大多数物种可以被描述为苯型，仅由稠合的6元环组成。我们应用CGT确定的直径参数，dS，观察到的，个人PAH的峰值，并证明观察到的PAH物种集群lowdS附近，高度浓缩的结构，与相对较低的人口的边缘duplex（扶手椅，海湾，峡湾）。最后，我们定量探索PAH异构体的相对稳定性使用基团加和性估计（苯型结构）和那些含有一个单一的5元环，使用密度泛函理论。对于后者，我们表明，高度凝聚，苯型结构具有较低的自由能比那些含有五元环，掩埋的5元环显示出最高的自由能。
Our laboratory recently published data that showed that the PAH composition of soot can be exactly determined and spatially resolved by low-fluence laser desorption ionization, coupled with high-resolution mass spectrometry imaging [1]. This analysis revealed that PAHs of 239–838 Da, containing few oxygenated species, comprise the soot observed in an ethylene diffusion flame. In this paper, we demonstrate that the empirical formula of observed species can aid in the enumeration of isomers and places limits on their structures and thermodynamic stability. Specifically, chemical graph theory (CGT) shows that the vast majority of species observed in the sampled particulate matter may be described as benzenoid, consisting of only fused 6-membered rings. We apply CGT to determine the Dias Parameter,dS, for observed, individual PAH peaks and demonstrate that observed PAH species cluster near lowdS, indicative of highly condensed structures, with relatively low populations of edge concavity (armchairs, bays, and fjords). Finally, we quantitatively explore the relative stability of PAH isomers using group-additivity estimates (for benzenoid structures) and those containing a single 5-membered rings using density functional theory. For the latter, we show that highly-condensed, benzenoid structures have lower free energy than those containing five-membered rings, with buried 5-membered rings showing the highest free energies.