IR Cavity Ringdown Spectroscopy and Density Functional Theory for Jet-Cooled Pyrrole?Cyclopentanone Binary Clusters: Effect of Pseudorotation on N?H・・・O?C Hydrogen Bonds
IR Cavity Ringdown Spectroscopy and Density Functional Theory for Jet-Cooled Pyrrole?Cyclopentanone Binary Clusters: Effect of Pseudorotation on N?H・・・O?C Hydrogen Bonds
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喷射冷却吡咯·环戊酮二元簇的红外腔衰荡光谱和密度泛函理论：赝旋转对 N?H・・・O?C 氢键的影响
DOI：
10.1021/acs.jpca.0c00794
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
Honma Kenji
中科院分区：
文献类型：
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作者：
Matsumoto Yoshiteru;Honma Kenji
N-H···O·C氢键（H-键）的几何构型和能量对于理解生物分子（如蛋白质和DNA）的稳定性和柔性是重要的。喷流冷却的吡咯-环戊酮（Py-Cp）二元团簇是从微观角度研究N-H···O·C氢键的合适模型。在本研究中，我们利用红外光腔衰荡光谱观察到Py-Cp二元团簇的NH伸缩振动。此外，密度泛函理论计算揭示了各种尺寸二元团簇的几何结构、简谐振动、分子间能量和供体-受体相互作用。测量了Py和Cp在He缓冲气体中超音速膨胀时不同蒸汽压条件下Py-Cp二元团簇的红外光谱。的蒸气压上的IR带强度的依赖性提供的NH伸缩振动，这是再现的Py 1-Cp 1，Py 1-Cp 2，和Py 2-Cp 1的计算频率的振动分配。为了区分由于Cp分子的假旋转而引起的几个NH同分异构结构的伸展，还应用了在He缓冲气体中混合Ar的超声膨胀来产生Py 1-Cp 2。Py 1-Cp 1是由N-H···O-CN氢键形成的。Py 1-Cp 2是由Py和两个Cp分子之间的N-H···O-CN-氢键和堆积作用形成的环状结构。Py 2-Cp 1也具有环状结构，该环状结构不仅由两个Py分子之间的N-H···O-CN-H-键形成，而且还由两个Py分子之间的N-H···π-H-键以及Py和Cp之间的堆积相互作用形成。Py 2-Cp 1与相应的吡咯-丙酮二元团簇的氢键几何构型的比较表明，Py和Cp之间的堆积作用通过协同效应加强了N-H···O-CN-C氢键.
The geometry and energetics of the N—H···O═C hydrogen bond (H-bond) are important to understand the stability and flexibility of biomolecules, such as protein and DNA. Jet-cooled pyrrole–cyclopentanone (Py–Cp) binary clusters are appropriate models to investigate the N—H···O═C H-bond from a microscopic point of view. In this study, NH stretching vibrations of the Py–Cp binary clusters were observed by IR cavity ringdown spectroscopy. Furthermore, density functional theory calculations revealed geometric structures, harmonic vibrations, intermolecular energies, and donor–acceptor interactions for various sizes of binary clusters. The IR spectra of the Py–Cp binary clusters were measured under various conditions of the vapor pressures of Py and Cp in He buffer gas for a supersonic expansion. The dependence of the IR band intensities on the vapor pressure provides vibrational assignments of the NH stretching vibrations, which were reproduced by calculated frequencies of Py1–Cp1, Py1–Cp2, and Py2–Cp1. An admixture of Ar in He buffer gas for a supersonic expansion was also applied to produce Py1–Cp2in order to differentiate several NH stretches of isomeric structures due to the pseudorotation of Cp molecules. Py1–Cp1is formed by the N—H···O═C H-bond. Py1–Cp2has a cyclic structure that is formed by the N—H···O═C H-bond and stacking interactions among Py and two Cp molecules. Py2–Cp1also has a cyclic structure that is formed by not only the N—H···O═C H-bond but also a N—H···π H-bond between two Py molecules and a stacking interaction between Py and Cp. A comparison of the H-bond geometries between Py2–Cp1and the corresponding pyrrole–acetone binary cluster reveals that the stacking interaction between Py and Cp strengthens the N—H···O═C H-bond through a cooperative effect.