Kim Hugh I, Johnson Paul V, Beegle Luther W, Beauchamp J L, Kanik Isik
Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, USA.
J Phys Chem A. 2005 Sep 8;109(35):7888-95. doi: 10.1021/jp051274h.
A number of carboxylate anions spanning a mass range of 87-253 amu (pyruvate, oxalate, malonate, maleate, succinate, malate, tartarate, glutarate, adipate, phthalate, citrate, gluconate, 1,2,4-benzenetricarboxylate, and 1,2,4,5-benzenetetracarboxylate) were investigated using electrospray ionization ion mobility spectrometry. Measured ion mobilities demonstrated a high correlation between mass and mobility in both N2 and CO2 drift gases. Such a strong mass-mobility correlation among structurally dissimilar ions suggests that the carboxylate functional group that these ions have in common is the source of the correlation. Computational analysis was performed to determine the most stable conformation of the studied carboxylate anions in the gas phase under the current experimental conditions. This analysis indicated that the most stable conformations for multicarboxylate anions included intramolecular hydrogen-bonded ring structures formed between the carboxylate group and the neutral carboxyl group. The carboxylate anions that form ring confirmations generally show higher ion mobility values than those that form extended conformations. This is the first observation of intramolecular hydrogen-bonded ring conformation of carboxylate anions in the gas phase at atmospheric pressure.
使用电喷雾电离离子迁移谱法研究了一系列质量范围为87 - 253原子质量单位的羧酸根阴离子（丙酮酸根、草酸根、丙二酸根、马来酸根、琥珀酸根、苹果酸根、酒石酸根、戊二酸根、己二酸根、邻苯二甲酸根、柠檬酸根、葡萄糖酸根、1,2,4 - 苯三甲酸根和1,2,4,5 - 苯四甲酸根）。在氮气和二氧化碳漂移气体中，测得的离子迁移率表明质量与迁移率之间存在高度相关性。结构不同的离子之间如此强的质量 - 迁移率相关性表明这些离子共有的羧酸根官能团是相关性的来源。进行了计算分析，以确定在当前实验条件下气相中所研究羧酸根阴离子的最稳定构象。该分析表明，多羧酸根阴离子的最稳定构象包括羧酸根基团与中性羧基之间形成的分子内氢键环结构。形成环状构象的羧酸根阴离子通常比形成伸展构象的羧酸根阴离子具有更高的离子迁移率值。这是在大气压下气相中羧酸根阴离子分子内氢键环构象的首次观察。
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