Tracking the Structural Evolution of 4-Aminobenzoic Acid in the Transition from Solution to the Gas Phase
Tracking the Structural Evolution of 4-Aminobenzoic Acid in the Transition from Solution to the Gas Phase
复制标题
追踪 4-氨基苯甲酸从溶液到气相转变过程中的结构演变
DOI：
10.1021/acs.jpcb.9b10576
复制
发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Russell, David H.
中科院分区：
文献类型：
--
作者：
Hebert, Michael J.;Russell, David H.
在这里，低温离子迁移率质谱（cryo-IM-MS）是用来调查从溶液到气相过渡过程中的簇内质子转移反应的4-氨基苯甲酸。以前的研究表明，4-氨基苯甲酸（4-ABAH+）的胺基质子化有利于在溶液中（N-质子体），而羧酸基团的质子化有利于在气相中（O-质子体）。水合4-ABAH+离子（4-ABAH+（H2O）n）的cryo-IM-MS（80 K）研究结果被解释为质子转移反应通过连接−NH3+和−COOH基团的水桥（n = 6）发生的证据，即Grotthuss机制。水分子的弱结合能限制了获得水合离子的第一性原理碰撞截面（CCS）;因此，通过将实验到达时间分布与理论确定的CCS相关联，推导出4-ABAH+（H2O）0- 6离子的候选结构。据我们所知，这些是水合离子CCS的第一原理测定。非极性共溶剂，特别是乙腈，已被假定为通过阻断Grotthuss机制来抑制质子转移，但我们的数据表明，乙腈只是稳定铵离子。
Here, cryogenic ion mobility-mass spectrometry (cryo-IM-MS) is used to investigate intracluster proton transfer reactions of 4-aminobenzoic acid during the transition from solution to the gas phase. Previous studies have shown that protonation of the amine group of 4-aminobenzoic acid (4-ABAH+) is favored in solution (N-protomer), whereas protonation of the carboxylic acid group is favored in the gas phase (O-protomer). Results from cryo-IM-MS (80 K) studies of hydrated 4-ABAH+ions, 4-ABAH+(H2O)n, are interpreted as evidence that the proton transfer reaction occurs through a water bridge atn= 6 connecting the −NH3+and −COOH groups, that is,a Grotthuss mechanism. The weak binding energy of water molecules imposes limits for obtaining first-principles collisional cross sections (CCSs) of hydrated ions; consequently, candidate structures for 4-ABAH+(H2O)0–6ions are derived by correlating experimental arrival-time distributions to theoretically determined CCSs. To our knowledge, these are the first first-principles determinations of CCS for hydrated ions. Apolar cosolvents, particularly acetonitrile, have been postulated to inhibit proton transfer by blocking the Grotthuss mechanism, but our data suggest that acetonitrile simply stabilizes the ammonium ion.