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VUV Photoionization and Dissociation of Tyramine and Dopamine: the Joint Experimental and Theoretical Studies
Hui-jun Guo,Li-li Ye,Liang-yuan Jia,Li-dong Zhang*,Fei Qi
Author NameAffiliationE-mail
Hui-jun Guo National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China  
Li-li Ye National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China  
Liang-yuan Jia National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China  
Li-dong Zhang* National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China zld@ustc.edu.cn 
Fei Qi National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China  
Abstract:
Photon induced dissociation investigations of neutral tyramine and dopamine are carried out with synchrotron vacuum ultraviolet photoionization mass spectrometry and theoretical calculations. At low photon energy, only molecular ions are measured by virtue of near-threshold photoionization. While increasing photon energy to 11.7 eV or more, four distinct fragment ions are obtained for tyramine and dopamine, respectively. Besides, the ioniza-tion energies of tyramine and dopamine are determined to be 7.98±0.05 and 7.67±0.05 eV by measuring the photoionization efficiency curves of corresponding molecular ions. With help of density function theory calculations, the detailed fragmentation pathways are es-tablished as well. These two molecular cations have similar aminoethyl group elimination pathways, C7H8O2(m/z=124) and C7H8O(m/z=108) are supposed to be generated by the McLafferty rearrangement via γ-hydrogen (γ-H) shift inducing β-fission. And CH2NH2+ is proposed to derive from the direct fission of C7-C8 bond. Besides, the McLafferty rear-rangement and the C7-C8 bond fission are validated to be dominant dissociation pathways for tyramine and dopamine cations.
Key words:  Tyramine, Dopamine, VUV photoionization, Mass spectrometry, Ionization energy, Dissociation pathway
FundProject:
酪胺和多巴胺VUV光电离/解离的实验和理论研究
郭会军,叶莉莉,贾良元,张李东*,齐飞
摘要:
利用同步辐射真空紫外光电离质谱和理论计算对中性酪胺和多巴胺分子的光诱导解离过程进行研究.在较低光子能量下,通过近阈光电离仅得到母体离子信号.当增加光子能量到11.7 eV甚至更高时,从酪胺和多巴胺分别得到四个清晰可辨的碎片离子信号.另外通过测量母体离子的光电离效率曲线,酪胺和多巴胺分子的电离能分别为7.98和7.67 eV(实验误差为±0.05 eV).结合理论计算建立这两个分子的详细碎裂路径,包括相似的胺乙基消除路径.其中碎片C7H8O2(m/z=124)和C7H8O(m/z=108)的生成认为来自McLafferty重排,该过程经历分子内的γ氢迁移诱导的β开裂反应. 另外,C7-C8键直接开裂可以生成CH2NH2+(m/z=30)碎片离子,并且该过程和McLafferty重排为主要的裂解路径.
关键词:  酪胺,多巴胺,VUV光电离,质谱,电离能,解离路径
DOI:10.1088/1674-0068/25/01/11-18
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