Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan.
Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.
Phys Chem Chem Phys. 2022 Mar 9;24(10):5774-5779. doi: 10.1039/d1cp05762f.
The protonation site of molecules can be varied by their surrounding environment. Gas-phase studies, including the popular techniques of infrared spectroscopy and ion mobility spectrometry, are a powerful tool for the determination of protonation sites in solvated clusters but often suffer from inherent limits for larger hydrated clusters. Here, we present collision-assisted stripping infrared (CAS-IR) spectroscopy as a new technique to overcome these problems and apply it in a proof-of-principle experiment to hydrated clusters of protonated benzocaine (HBC), which shows protonation-site switching depending on the degree of hydration. The most stable protomer of HBC in the gas phase (O-protonated) is interconverted into its most stable protomer in aqueous solution (N-protonated) upon hydration with three water molecules. CAS-IR spectroscopy enables us to unambiguously assign protonation sites and quantitatively determine the relative abundance of various protomers.
分子的质子化位置可以通过其周围环境发生变化。气相研究，包括红外光谱和离子淌度谱等流行技术，是确定溶剂化团簇中质子化位置的有力工具，但对于较大的水合团簇往往受到固有限制。在这里，我们提出了碰撞辅助去卷积红外（CAS-IR）光谱作为一种克服这些问题的新技术，并将其应用于质子化苯佐卡因（HBC）水合团簇的原理验证实验中，该实验表明质子化位置取决于水合程度发生切换。在气相中，HBC 的最稳定单体（O-质子化）在与三个水分子水合后，转化为其在水溶液中的最稳定单体（N-质子化）。CAS-IR 光谱使我们能够明确分配质子化位置并定量确定各种单体的相对丰度。
