Infrared Multiphoton Dissociation Spectroscopy Study of Protonated p-Aminobenzoic Acid: Does Electrospray Ionization Afford the Amino- or Carboxy-Protonated Ion?
Infrared Multiphoton Dissociation Spectroscopy Study of Protonated p-Aminobenzoic Acid: Does Electrospray Ionization Afford the Amino- or Carboxy-Protonated Ion?
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DOI：
10.1021/jp203829z
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发表时间：
2011-07-07
影响因子：
2.9
通讯作者：
Kass, Steven R.
中科院分区：
文献类型：
--
作者：
Schmidt, Jacob;Meyer, Matthew M.;Kass, Steven R.
用电喷雾电离（ESI）方法，在2800-4000 cm（-1）的气相中，记录了对氨基苯甲酸质子化产物的红外多光子解离光谱。O-质子化离子在气相中比N-质子化结构更稳定，而在两种溶液中情况正好相反。当使用CH_3OH/H_2O作为ESI溶剂时，仅观察到O-质子化离子。相比之下，由CH 3CN/H2O产生O-和N-质子化物质的70：30混合物。这些结构的分配是基于各种各样的实验数据（作用光谱，photoregradation，photoregradation动力学和H/D交换），并充分支持广泛的计算。这项工作表明，ESI可以导致异构化，并且可以通过改变分析底物的溶剂来改变电离位点。
Infrared multiphoton dissociation spectra of protonated p-aminobenzoic acid generated by electrospray ionization (ESI) from aqueous methanol and acetonitrile solutions were recorded in the gas phase from 2800-4000 cm(-1). The O-protonated ion is more stable than the N-protonated structure in the gas phase, whereas the opposite is true in both solutions. When CH3OH/H2O was used as the ESI solvent, only the O-protonated ion was observed. In contrast, a 70:30 mixture of the O- and N-protonated species were produced from CH3CN/H2O. These structural assignments are based on an assortment of experimental data (action spectra, photofragments, photofragmentation kinetics, and H/D exchange) and are fully supported by extensive computations. This work shows that ESI can lead to isomerization and that the ionization site may be varied by changing the solvent from which the substrate is analyzed.