Lou Xianwen, van den Hout Kelly P, van Houtem Michel H C J, van Dongen Joost L J, Vekemans Jef A J M, Meijer E W
Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
J Mass Spectrom. 2006 May;41(5):659-69. doi: 10.1002/jms.1025.
Four C3-symmetrical tris(dipeptide) disks and their precursors were characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS). The C3-symmetrical disks were based on a benzene-1,3,5-triscarboxamide core extended by oligopeptides with trialkoxyanilide tails. The results indicate that MALDI TOF MS is a powerful and straightforward analytical technique for characterizing C3-symmetrical disks and their precursors. Clear (pseudo)-molecular ion peaks could readily be identified. It is remarkable that strong radical ion signals were observed for all the compounds, including the anilines that were expected to be protonated prior to laser irradiation using acidic MALDI matrixes. Possible mechanisms for radical ion formation were investigated with the employment of radical scavengers, with various matrixes and with direct laser desorption/ionization (LDI). Most likely the radicals are formed by losing one electron from the aniline nitrogen and stabilized by conjugation through the phenyl ring. It appears that direct photo/thermal ionization of analytes is an important route for the radical ion formation of the compounds with trialkoxy aniline/anilide groups.
使用基质辅助激光解吸/电离飞行时间质谱（MALDI TOF MS）对四个C3对称的三（二肽）盘及其前体进行了表征。这些C3对称盘基于由带有三烷氧基苯胺尾部的寡肽延伸的苯-1,3,5-三羧酰胺核心。结果表明，MALDI TOF MS是一种用于表征C3对称盘及其前体的强大且直接的分析技术。清晰的（准）分子离子峰很容易被识别。值得注意的是，所有化合物都观察到了强烈的自由基离子信号，包括预期在使用酸性MALDI基质进行激光照射之前会被质子化的苯胺。通过使用自由基清除剂、各种基质以及直接激光解吸/电离（LDI）研究了自由基离子形成的可能机制。最有可能的是，自由基是通过从苯胺氮原子上失去一个电子形成的，并通过苯环共轭而稳定。看来，分析物的直接光/热电离是具有三烷氧基苯胺/苯胺基团的化合物形成自由基离子的重要途径。
