Ohshimo Keijiro, Sato Ryosuke, Takasaki Yuya, Tsunoda Kengo, Ito Ryosuke, Kanno Manabu, Misaizu Fuminori
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
J Phys Chem Lett. 2023 Sep 21;14(37):8281-8288. doi: 10.1021/acs.jpclett.3c01996. Epub 2023 Sep 7.
Proton transfer is classified into two mechanisms: the Grotthuss (proton-relay) and vehicle mechanisms. It has been well studied on gas-phase proton transfer by a proton relay involving multiple molecules. However, a vehicle mechanism in which a single molecule transports a proton has rarely been reported. Here, we have obtained clear evidence that the proton transfers efficiently between the two protonation sites in protonated -aminobenzoic acid (PABA·H) by a single ammonia molecule as a vehicle. The gaseous PABA·H ions were reacted with NH or ND under single-collision conditions in a cold ion trap, and the proton-transferred ions were identified by cryogenic ion mobility-mass spectrometry. A reaction intermediate PABA·H·NH was also detected for the first time. The reaction pathway search calculations and molecular dynamics simulations supported the present experimental finding that intramolecular proton transfer occurs very efficiently by the vehicle mechanism.
Grotthuss（质子接力）机制和载体机制。通过涉及多个分子的质子接力对气相质子转移进行了充分研究。然而，很少有报道涉及单个分子传输质子的载体机制。在此，我们获得了明确的证据，表明单个氨分子作为载体可使质子在质子化对氨基苯甲酸（PABA·H）的两个质子化位点之间高效转移。气态PABA·H离子在冷离子阱中于单碰撞条件下与NH或ND反应，通过低温离子淌度-质谱法鉴定质子转移离子。还首次检测到反应中间体PABA·H·NH。反应途径搜索计算和分子动力学模拟支持了目前的实验发现，即通过载体机制分子内质子转移非常高效地发生。
