Yuyao Yang, Ruoqi Zhao, Wenkai Zhang, Jiali Gao, Feng Gai
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To test this possibility, herein we combine molecular dynamics simulations and quantum mechanical calculations to assess the effect of H-bonding interactions on the νCN of 5-cyanoindole (5-CNI) in its different electronic states. We find that its C≡N group can form either one H-bond (single-H-bond) or two H-bonds (d-H-bonds) with the solvent molecules and that in the ground electronic state, a single-H-bond can lead νCN to shift either to a higher or lower frequency, depending on its angle, which is consistent with previous studies, whereas the d-H-bonds cause νCN to redshift. 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引用次数: 0
摘要
腈基(C≡N)伸展振动被广泛用作蛋白质的特定位点环境探针,因此,许多计算研究都用来研究影响其频率(νCN)的因素。这些研究大多是在相关分子的基态电子状态下进行的,研究结果表明,与腈基形成正常或线性氢键(H 键)会导致其 νCN 发生蓝移。然而,最近的一些实验研究表明,对于某些芳香族腈,其激发电子态的溶剂弛豫会导致νCN 在质子(非质子)溶剂中发生红移(蓝移),这表明氢键(H-bonding)相互作用对νCN 的影响可能取决于分子的电子态。为了验证这种可能性,我们在本文中结合分子动力学模拟和量子力学计算,评估了氢键相互作用对不同电子态的 5-氰基吲哚(5-CNI)νCN 的影响。我们发现,5-氰基吲哚的 C≡N 基团可以与溶剂分子形成一个 H 键(单 H 键)或两个 H 键(d-H 键),在基态电子状态下,单 H 键会导致 νCN 根据其角度的不同向更高或更低的频率移动,这与之前的研究一致,而 d-H 键会导致 νCN 重移。然而,在具有电荷转移态特征的最低激发电子态(即 S1)中,所有 H 键都会引起 νCN 的红移,其中 d-H 键在这方面最为有效。
Blueshift or redshift? Effect of hydrogen bonding interactions on the C≡N stretching frequency of 5-cyanoindole.
The nitrile (C≡N) stretching vibration is widely used as a site-specific environmental probe of proteins and, as such, many computational studies have been used to investigate the factors that affect its frequency (νCN). These studies, most of which were carried out in the ground electronic state of the molecule of interest, revealed that the formation of a normal or linear hydrogen bond (H-bond) with the nitrile group results in a blueshift in its νCN. Recently, however, several experimental studies showed that for certain aromatic nitriles, solvent relaxations in their excited electronic state(s) induce a redshift (blueshift) in νCN in protic (aprotic) solvents, suggesting that the effect of hydrogen-bonding (H-bonding) interactions on νCN may depend on the electronic state of the molecule. To test this possibility, herein we combine molecular dynamics simulations and quantum mechanical calculations to assess the effect of H-bonding interactions on the νCN of 5-cyanoindole (5-CNI) in its different electronic states. We find that its C≡N group can form either one H-bond (single-H-bond) or two H-bonds (d-H-bonds) with the solvent molecules and that in the ground electronic state, a single-H-bond can lead νCN to shift either to a higher or lower frequency, depending on its angle, which is consistent with previous studies, whereas the d-H-bonds cause νCN to redshift. However, in its lowest-lying excited electronic state (i.e., S1), which has the characteristics of a charge-transfer state, all H-bonds induce a redshift in νCN, with the d-H-bonds being most effective in this regard.
期刊介绍:
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