Solvation in electrospray mass spectrometry: effects on the reaction kinetics of fragmentation mediated by ion-neutral complexes.
Solvation in electrospray mass spectrometry: effects on the reaction kinetics of fragmentation mediated by ion-neutral complexes.
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DOI：
10.1021/jo050398n
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发表时间：
2005-05
期刊：
影响因子：
--
通讯作者：
Yaping Tu;Limin He;W. Fitch;Michelle Lam
中科院分区：
文献类型：
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作者：
Yaping Tu;Limin He;W. Fitch;Michelle Lam
在三重四极杆质谱仪上的电喷雾电离（ESI）中，具有N，N-二甲基氨基丙氧基侧链的分子苄达明在Q1扫描中显示出与其MH（+）离子的质量选择性碰撞诱导解离（CID）显著不同的碎裂模式。在较高能量下在Q1扫描中占主导地位的N，N-二甲基亚铵离子在所有CID光谱中仅是次要产物。通过使用较小的模型分子N，N，N '，N'-四甲基-1，3-丙二胺，测量相应反应的动能释放，我们证明了由N，N-二甲基氮杂环丁烷阳离子和中性对应物组成的离子-中性络合物。当离子-中性络合物中间体向消除方向发展形成亚铵离子时，过渡态被中性物质稳定。溶剂化的离子中性复合物，这阻碍了分离的两个合作伙伴所产生的更紧密的外壳，有利于消除通过提高过渡态的稳定。因此，在Q1扫描中亚铵离子的普遍存在是ESI源中溶剂化的结果。在CID反应中，其中分解离子是质量选择的，因此溶剂化不存在，亚铵离子是次要产物，离子-中性络合物的分离成为主导。
In electrospray ionization (ESI) on a triple quadrupole mass spectrometer, benzydamine, a molecule with an N,N-dimethylaminopropoxyl side chain, showed a fragmentation pattern in Q1 scans that is dramatically different from the mass-selected collision-induced dissociation (CID) of its MH(+) ion. The N,N-dimethylimmonium ion, which dominates in Q1 scans at higher energies, is only a minor product in all CID spectra. By using a smaller model molecule, N,N,N',N'-tetramethyl-1,3-propanediamine, with the kinetic energy release measured for the corresponding reaction, we have demonstrated that an ion-neutral complex composed of the N,N-dimethylazetidine cation and a neutral counterpart is involved. When the ion-neutral complex intermediate evolves toward elimination to form the immonium ion, the transition state is stabilized by the neutral species. Solvation of the ion-neutral complex, which obstructs the separation of the two partners by the resulting tighter enclosure, facilitates the elimination by enhancing the stabilization of the transition state. Therefore, the prevalence of the immonium ion in Q1 scans was a result of solvation in the ESI source. In CID reactions, where the decomposing ions are mass-selected and thus solvation does not exist, the immonium ion was a minor product, and the separation of the ion-neutral complex became dominant.