Arildii Dashjargal, Matsumoto Yoshiteru, Dopfer Otto
Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany.
Department of Chemistry, Faculty of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529, Japan.
J Phys Chem A. 2023 Mar 23;127(11):2523-2535. doi: 10.1021/acs.jpca.3c00363. Epub 2023 Mar 10.
Microhydration of heterocyclic aromatic molecules can be an appropriate fundamental model to shed light on intermolecular interactions and functions of macromolecules and biomolecules. We characterize herein the microhydration process of the pyrrole cation (Py) by infrared photodissociation (IRPD) spectroscopy and dispersion-corrected density functional theory calculations (B3LYP-D3/aug-cc-pVTZ). Analysis of IRPD spectra of mass-selected Py(HO) and its cold Ar-tagged cluster in the NH and OH stretch range combined with geometric parameters of intermolecular structures, binding energies, and natural atomic charge distribution provides a clear picture of the growth of the hydration shell and cooperativity effects. Py(HO) is formed by stepwise hydration of the acidic NH group of Py by a hydrogen-bonded (HO) chain with NH···OH···OH configuration. In this linear H-bonded hydration chain, strong cooperativity, mainly arising from the positive charge, strengthens both the NH···O and OH···O H-bonds with respect to those of PyHO and (HO), respectively. The linear chain structure of the Py(HO) cation is discussed in terms of the ionization-induced rearrangement of the hydration shell of the neutral Py(HO) global minimum characterized by the so-called "σ-π bridge structure" featuring a cyclic NH···OH···OH···π H-bonded network. Emission of the π electron from Py by ionization generates a repulsive interaction between the positive π site of Py and the π-bonded OH hydrogen of (HO), thereby breaking this OH···π hydrogen bond and driving the hydration structure toward the linear chain motif of the global minimum on the cation potential.
杂环芳香分子的微水合作用可以作为一个合适的基础模型，以阐明大分子和生物分子的分子间相互作用及功能。我们在此通过红外光解离（IRPD）光谱和色散校正密度泛函理论计算（B3LYP-D3/aug-cc-pVTZ）对吡咯阳离子（Py）的微水合过程进行了表征。对质量选择的Py(HO)及其在NH和OH伸缩范围内的冷Ar标记簇的IRPD光谱进行分析，并结合分子间结构的几何参数、结合能和自然原子电荷分布，清晰地描绘了水合壳的生长和协同效应。Py(HO)是由具有NH···OH···OH构型的氢键（HO）链逐步水合Py的酸性NH基团形成的。在这个线性氢键水合链中，主要由正电荷引起的强协同作用分别相对于PyHO和（HO）的氢键增强了NH···O和OH···O氢键。Py(HO)阳离子的线性链结构是根据中性Py(HO)全局最小值的水合壳的电离诱导重排来讨论的，其特征是具有循环NH···OH···OH···π氢键网络的所谓“σ-π桥结构”。电离使Py发射π电子，在Py的正π位点和（HO）的π键合OH氢之间产生排斥相互作用，从而打破这个OH···π氢键，并将水合结构驱动到阳离子势面上全局最小值的线性链基序。
