Felder Thorsten, Schalley Christoph A, Fakhrnabavi Hassan, Lukin Oleg
Kekulé-Institut für Organische Chemie und Biochemie der Universität, Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany.
Chemistry. 2005 Sep 19;11(19):5625-36. doi: 10.1002/chem.200401236.
Mass spectrometry, in particular MALDI-MS, has often been used as a valuable means to characterize dendritic molecules with respect to their molecular masses. Also, it is a valuable tool for analyzing potential defects in their structure which result from incomplete synthetic steps. This article presents a comparison of ESI and MALDI mass spectrometric experiments on dendrimers persulfonylated at their periphery. While the ESI mass spectra easily permit impurities and defects to be identified and thus provide evidence for sample purity, reactions with acidic matrices occur during the MALDI process. The resulting defects are identical to those expected from incomplete substitution. Thus, in these cases, MALDI-MS yields false negative results. With mass-selected, ESI-generated ions, collision experiments were performed in an FT-ICR mass spectrometer cell to provide detailed insight into the fragmentation patterns of the various dendrimers. Different fragmentation patterns are observed depending on the exact structure of the dendrimer. Also, the nature of the charge is important. The fragmentation reactions for protonated species differ much from those binding a sodium or potassium ion. These differences can be traced back to different sites for binding H+ versus Na+ or K+. Tandem MS experiments on mass-selected dendrimer ions with defects can be used to distinguish different types of defects. A concise structural assignment can thus be made on the basis of these experiments. Even mixtures of two isobaric defect variants with the same elemental composition can be identified.
质谱分析法，尤其是基质辅助激光解吸电离质谱（MALDI-MS），常被用作表征树枝状分子分子量的重要手段。此外，它还是分析因合成步骤不完全而导致的潜在结构缺陷的宝贵工具。本文介绍了对在其外围进行全磺酰化的树枝状聚合物进行电喷雾电离（ESI）和基质辅助激光解吸电离（MALDI）质谱实验的比较。虽然电喷雾电离质谱很容易识别杂质和缺陷，从而为样品纯度提供证据，但在基质辅助激光解吸电离过程中会发生与酸性基质的反应。由此产生的缺陷与不完全取代预期的缺陷相同。因此，在这些情况下，基质辅助激光解吸电离质谱会产生假阴性结果。利用质量选择的、由电喷雾电离产生的离子，在傅里叶变换离子回旋共振（FT-ICR）质谱仪池中进行了碰撞实验，以深入了解各种树枝状聚合物的碎裂模式。根据树枝状聚合物的确切结构观察到不同的碎裂模式。此外，电荷的性质也很重要。质子化物种的碎裂反应与结合钠或钾离子的反应有很大不同。这些差异可追溯到结合H⁺与Na⁺或K⁺的不同位点。对有缺陷的质量选择树枝状聚合物离子进行串联质谱实验可用于区分不同类型的缺陷。因此，可以根据这些实验进行精确的结构归属。甚至可以识别具有相同元素组成的两种等压缺陷变体的混合物。
