Department of Chemistry, University of New Orleans, 2000 Lakeshore Dr., New Orleans, LA 70148, USA.
J Mass Spectrom. 2012 Aug;47(8):995-1003. doi: 10.1002/jms.3027.
The most common secondary-ionization mechanism in positive ion matrix-assisted laser desorption/ionization (MALDI) involves a proton transfer reaction to ionize the analyte. Peptides and proteins are molecules that have basic (and acidic) sites that make them susceptible to proton transfer. However, non-polar, aprotic compounds that lack basic sites are more difficult to protonate, and creating charged forms of this type of analyte can pose a problem when conventional MALDI matrices are employed. In this case, forming a radical molecular ion through electron transfer is a viable alternative, and certain matrices may facilitate the process. In this work, we investigate the performance of a newly developed electron-transfer secondary reaction matrix: 9,10-diphenylanthracene (9,10-DPA). The use of 9,10-DPA as matrix for MALDI analysis has been tested using several model compounds. It appears to promote ionization through electron transfer in a highly efficient manner as compared to other potential matrices. Thermodynamic aspects of the observed electron transfers in secondary-ionization reactions were also considered, as was the possibility for kinetically controlled/endothermic, electron-transfer reactions in the MALDI plume.
正离子基质辅助激光解吸/电离（MALDI）中最常见的二次离子化机制涉及质子转移反应以电离分析物。肽和蛋白质是具有碱性（和酸性）位点的分子，使它们容易发生质子转移。然而，缺乏碱性位点的非极性、非质子性化合物更难质子化，并且当使用常规 MALDI 基质时，会对这种分析物的带电形式的形成造成问题。在这种情况下，通过电子转移形成自由基分子离子是一种可行的替代方法，某些基质可能会促进该过程。在这项工作中，我们研究了一种新开发的电子转移次级反应基质：9,10-二苯基蒽（9,10-DPA）的性能。使用几种模型化合物测试了 9,10-DPA 作为 MALDI 分析基质的用途。与其他潜在基质相比，它似乎以高效的方式通过电子转移促进了离子化。还考虑了次级离子化反应中观察到的电子转移的热力学方面，以及 MALDI 羽流中动力学控制/吸热电子转移反应的可能性。
