School of Chemical and Environmental Engineering, Anhui Polytechnic University, Wuhu, 241000, Anhui Province, People's Republic of China.
School of the Environment, Nanjing University, Nanjing, 210093, People's Republic of China.
J Mol Model. 2023 Apr 15;29(5):142. doi: 10.1007/s00894-023-05553-0.
In this study, the reactions of hydrated electron (e(aq)) with alkyl and aryl halides were simulated with an ab initial molecular dynamics (AIMD) method to reveal the underlying mechanism. An original protocol was developed for preparing the proper initial wavefunction guess of AIMD, in which a single electron was curled in a tetrahedral cavity of four water molecules. Our results show that the stability of e(aq) increases with the hydrogen bond grid integrity. The organic halides prefer to react with e(aq) in neutral or alkaline environment, while they are more likely to react with hydrogen radical (the product of e(aq) and proton) under acidic conditions. The reaction between fluorobenzene/fluoromethane and hydrogen radical is considered as the least favorable reaction due to the highest reaction barriers. The bond dissociation energy (BDE) suggested that the cleavage of the carbon-halogen bond of their anion radical might be a thermodynamically favorable reaction. AIMD results indicated that the LUMO or higher orbitals were the e(aq) migration destination. The transplanted electron enhanced carbon-halogen bond vibration intensively, leading to bond cleavage. The solvation process of the departing halogen anions was observed in both fluorobenzene and fluoromethane AIMD simulation, indicating that it might have a significant effect on enthalpy. Side reactions and byproducts obtained during the AIMD simulation suggested the complexity of the e(aq) reactions and further investigation was needed to fully understand the reaction mechanisms. This study provided theoretical insight into the pollutant environmental fate and constructed a methodological foundation for AIMD simulation of analogous free radical reactions.
The theoretical calculation was conducted on the combination of Gaussian16 and ORCA5.0.3 software packages. The initial geometries, as well as the wavefunction initial guesses, were obtained at PBE0/ma-def2-TZVP/IEFPCM-water level in Gaussian16 unless otherwise stated. AIMD simulations were performed at the same level in ORCA. Wavefunction analysis was carried out with Multiwfn. The details methods were described in the section "Computational details" section.
在这项研究中，采用从头算分子动力学（AIMD）方法模拟了水化电子（e(aq)）与烷基和芳基卤化物的反应，以揭示其潜在的反应机制。我们开发了一种原始方案来制备适当的 AIMD 初始波函数猜测，其中一个电子卷曲在四个水分子的四面体腔中。结果表明，水化电子（e(aq)）的稳定性随氢键网格完整性的增加而增加。有机卤化物在中性或碱性环境中更倾向于与 e(aq)反应，而在酸性条件下则更倾向于与氢自由基（e(aq)和质子的产物）反应。由于反应势垒最高，因此认为氟苯/氟甲烷与氢自由基的反应是最不利的反应。根据键解离能（BDE），其阴离子自由基的碳卤键的断裂可能是热力学有利的反应。AIMD 结果表明，最低未占分子轨道（LUMO）或更高轨道是 e(aq)迁移的目的地。迁移电子增强了碳卤键的振动，导致键的断裂。在氟苯和氟甲烷 AIMD 模拟中都观察到离去卤素阴离子的溶剂化过程，这表明它可能对焓有显著影响。AIMD 模拟中得到的副反应和副产物表明 e(aq)反应的复杂性，需要进一步研究以充分了解反应机制。本研究为污染物环境归宿提供了理论见解，并为类似自由基反应的 AIMD 模拟构建了方法学基础。
理论计算结合使用 Gaussian16 和 ORCA5.0.3 软件包进行。除非另有说明，否则初始几何形状和波函数初始猜测均在 Gaussian16 中在 PBE0/ma-def2-TZVP/IEFPCM-水水平获得。在 ORCA 中以相同水平进行 AIMD 模拟。在 Multiwfn 中进行波函数分析。详情请参见“计算细节”部分。
