Yamagaki Tohru, Takeuchi Michika, Watanabe Takehiro, Sugahara Kohtaro, Takeuchi Takae
Suntory Foundation of Life Sciences, Bioorganic Research Institute, 8-1-1 Seikadai, Seika, Soraku, Kyoto, 619-0284, Japan.
Department of Chemistry, Faculty of Science, Nara Womens' University, Kitauoyanishi-machi, Nara, 630-8506, Japan.
Rapid Commun Mass Spectrom. 2016 Dec 30;30(24):2650-2654. doi: 10.1002/rcm.7761.
Proton and radical are transferred between matrices and matrix and analyte in matrix-assisted laser desorption/ionization (MALDI) and these transfers drive ionization of analytes. The odd-electron anion [M-2H] was generated in dihydroxybenzoic acids (DHBs) and the ion abundance of the 2,5-DHB was the highest among six DHB isomers. We were interested in the mechanism of the ion generation of the odd-electron anion.
The observed [M-2H] and [M-3H] ions, which were generated with the hydrogen radical removed from the phenolic hydroxyl groups (OH) in DHB isomers, were analyzed using negative-ion MALDI-MS. The enthalpy for ion generation and their stable structures were calculated using the density functional theory (DFT) calculation program Gaussian 09 with the B3LYP functional and the 6-31+G(d) basis set.
The number of observed [M-2H] and [M-3H] ions of the DHB isomers was dependent on the positions of the phenolic OH groups in the DHB isomers because the carboxy group interacts with the ortho OH group due to neighboring group participation, as confirmed from the stable structures of the [M-2H] anions calculated with the Gaussian 09 program. The DHB isomers were placed into three categories according to the number of the ions.
Odd-electron anions ([M-2H] ) and [M-2H -H] ([M-3H] ) ions were generated from DHB isomers due to removal of the hydrogen radical from the phenolic groups. The enthalpy for ion generation revealed that ion formation proceeds via a two-step pathway through the [M-M] ion as an intermediate. © 2016 The Authors. Rapid Communications in Mass Spectrometry Published by John Wiley & Sons Ltd.
在基质辅助激光解吸/电离（MALDI）过程中，质子和自由基在基质之间以及基质与分析物之间转移，这些转移驱动分析物的电离。在二羟基苯甲酸（DHBs）中产生了奇电子阴离子[M - 2H]，并且在六种DHB异构体中，2,5 - DHB的离子丰度最高。我们对奇电子阴离子的离子产生机制感兴趣。
使用负离子MALDI - MS分析了从DHB异构体中的酚羟基（OH）去除氢自由基后产生的观察到的[M - 2H]和[M - 3H]离子。使用密度泛函理论（DFT）计算程序Gaussian 09，采用B3LYP泛函和6 - 31 + G(d)基组计算离子产生的焓及其稳定结构。
DHB异构体的[M - 2H]和[M - 3H]离子的观察数量取决于DHB异构体中酚羟基的位置，因为羧基由于邻基参与与邻位OH基团相互作用，这从用Gaussian 09程序计算的[M - 2H]阴离子的稳定结构得到证实。根据离子数量，DHB异构体分为三类。
由于从酚基团去除氢自由基而从DHB异构体中产生了奇电子阴离子（[M - 2H]）和[M - 2H - H]（[M - 3H]）离子。离子产生的焓表明，离子形成通过以[M - M]离子为中间体的两步途径进行。© 2016作者。《质谱快报》由John Wiley & Sons Ltd出版
