Dual approach to vibrational spectra in solution: Microscopic influence of hydrogen bonding to the state of motion of glycine in water
Dual approach to vibrational spectra in solution: Microscopic influence of hydrogen bonding to the state of motion of glycine in water
复制标题
溶液中振动光谱的双重方法：氢键对水中甘氨酸运动状态的微观影响
DOI：
10.1021/ct500235a
复制
发表时间：
2014
期刊：
影响因子：
--
通讯作者：
M. Nagaoka
中科院分区：
文献类型：
--
作者：
Y. Kitamura;N. Takenaka;Y. Koyano;M. Nagaoka
我们提出了一种新的理论方法来阐明溶液中振动性质的微观本质，它包括振动频率分析（VFA）与两种Hessian矩阵的组合，即自由能表面上的有效Hessian（自由能Hessian：“FE-Hessian”）和瞬时Hessian（瞬时简正模Hessian：“INM-Hessian”）在QM/MM框架内。在这些VFA中，Hessian是通过解析方法获得的，与数值方法相比，从计算效率和精度方面都具有优势。在本研究中，我们已经将它们应用到甘氨酸水溶液。首先，我们利用VFA与FE-Hessian（VFA-FEH）方法，估计了溶剂水分子引起的振动频率移动。计算值与实验值定量一致。清楚地表明，这种振动位移不仅归因于结构弛豫，而且归因于明确的溶质-溶剂相互作用（即，原子间的相互作用）。第二，利用VFA结合INM-Hessian（VFA-INMH）方法，通过振动INM态密度（DOS）研究了溶液的振动光谱。通过光谱特征与甘氨酸分子周围微观溶剂化结构的比较，发现红外光谱的频移和带宽与氢键网络的形成密切相关。特别地，羟基和羰基振动态的瞬时变化与HB相互作用的强度呈明显相反的趋势，可以分别用成键轨道电子密度的直接变化和孤电子对与反键轨道之间的超共轭引起的间接变化这两种不同的机制很好地解释.总之，本文提出的对偶VFA方法是解释实验振动光谱微观起源的一个非常有用的策略。
We have proposed a new theoretical methodology to clarify the microscopic nature of the vibrational properties in solution, which consists of a combination of the vibrational frequency analyses (VFAs) with two kinds of Hessian matrices, that is, the effective Hessian on the free energy surface (free energy Hessian: “FE-Hessian”) and the instantaneous one (instantaneous normal mode Hessian: “INM-Hessian”) within QM/MM framework. In these VFAs, the Hessians were obtained by the analytical approach, having the advantages from the aspect of both the computational efficiency and accuracy in comparison to those obtained by the numerical one. In the present study, we have applied them to the glycine aqueous solution. First, by using the VFA with the FE-Hessian (VFA-FEH), we estimated the vibrational frequency shifts induced by solvent water molecules. The calculated values were quantitatively in agreement with experimental ones. It was clearly demonstrated that such vibrational shifts are attributed to not only the structural relaxation but also the explicit solute–solvent interactions (i.e., interatomic interactions). Second, by using the VFA with the INM-Hessian (VFA-INMH), the vibrational spectra in solution were investigated through the vibrational INM densities of states (DOS). By the comparison between the spectroscopic features and the microscopic solvation structure around glycine molecule, it was found that the frequency shifts and bandwidths in IR spectra are closely correlated with the hydrogen bonding (HB) network formations. In particular, the instantaneous changes of vibrational states of the hydroxyl group and carbonyl one, showing apparently inverse tendency on the strength of the HB interaction, can be explained very well on the basis of two different mechanisms, that is, the direct change of electron density in the bonding orbitals and the indirect one due to hyperconjugation between the lone electron pair and the antibonding orbitals, respectively. In conclusion, the present dual VFA approach is a quite useful strategy to interpret the microscopic origin of the experimental vibrational spectra.