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Computational study of the dimerization of glyphosate: mechanism and effect of solvent
RSC Advances ( IF 3.9 ) Pub Date : 2024-07-23 , DOI: 10.1039/d4ra04300f Sondes Meddeb-Limem 1 , Arij Ben Fredj 1
RSC Advances ( IF 3.9 ) Pub Date : 2024-07-23 , DOI: 10.1039/d4ra04300f Sondes Meddeb-Limem 1 , Arij Ben Fredj 1
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A computational study on the structure and stability of different series of glyphosate (Glyph) dimers comprising nonionized (N) and zwitterionic structures (Z) for neutral monomers, followed by an analysis of energetics of Glyph dimerization process have been performed by means of quantum chemical calculations in different media. Optimized geometries for energy minima, as well as relative potential and free energies of the possible various conformers of each series of Glyph dimer were computed as a function of the medium at B3LYP-D3/6-311++G(2d,2p) level. The solvation model based on density (SMD) is employed for all solution phase computations. Non-ionized dimers (DN), anion–cation (AC) and either zwitterion–zwitterion (DZP and DZC) or non-ionized-phosphonate zwitterion (NZP) ionized neutral forms of Glyph dimer are predicted to exist in the gas phase and in solution in large contrast to Glyph monomers. The DZC dimer form exhibiting a centrosymmetric arrangement of two carboxylate zwitterion units was found to be the most stable dimer structure in all media. In aqueous solution, the DZP and AC dimer type structures are significantly stabilized by hydration. The tautomerisms between DZC, DZP and AC dimer type structures have been investigated in the gas phase and in solution. The DZC type structures are more prone to experience proton transfer in water than in the gas phase and in cyclohexane. The mechanism for the tautomerization process in neutral ionized Glyph dimers proceeds via two direct proton transfer paths: DZP ![[leftrightharpoons]](https://www.rsc.org/images/entities/char_21cb.gif)
AC DZC. Results show that solvents play a key role in modulating the energetics of the dimerization process of Glyph. Solvation in cyclohexane, favors the dimerization process however, hydration opposed it. In aqueous solution, the mechanism of the dimerization of Glyph from its phosphonate zwitterionic monomer form (ZP) could be described by a set of equilibria including direct proton transfer paths as follows: 2ZP DZP AC DZC. According to our results, in aqueous solution, DZC Glyph dimers and their corresponding DZP and AC tautomers should be present in higher concentration than phosphonate zwitterionic Glyph monomers for high Glyph concentration, a fact that seems controversial in the literature.
中文翻译：
草甘膦二聚化的计算研究：机理和溶剂的影响
通过量子化学方法对不同系列的草甘膦（Glyph）二聚体（包括中性单体的非离子化（N）和两性离子结构（Z））的结构和稳定性进行了计算研究，随后对 Glyph 二聚过程进行了能量学分析不同介质中的计算。作为 B3LYP-D3/6-311++G(2d,2p) 水平上介质的函数，计算了能量最小值的优化几何形状，以及每个系列 Glyph 二聚体可能的各种构象异构体的相对势和自由能。所有溶液相计算均采用基于密度（SMD）的溶剂化模型。非离子化二聚体 (DN)、阴离子-阳离子 (AC) 和两性离子-两性离子（DZP 和 DZC）或非离子化磷酸两性离子 (NZP) 电离中性形式的 Glyph 二聚体预计存在于气相和与 Glyph 单体形成鲜明对比的解决方案。发现两个羧酸盐两性离子单元呈中心对称排列的 DZC 二聚体形式是所有介质中最稳定的二聚体结构。在水溶液中，DZP 和 AC 二聚体型结构通过水合显着稳定。已在气相和溶液中研究了 DZC、DZP 和 AC 二聚体型结构之间的互变异构现象。 DZC 型结构在水中比在气相和环己烷中更容易发生质子转移。中性离子化 Glyph 二聚体中的互变异构过程的机制通过两个直接质子转移路径进行：DZP 交流电 DZC。结果表明，溶剂在调节 Glyph 二聚过程的能量方面发挥着关键作用。环己烷中的溶剂化有利于二聚过程，但水合作用则相反。 在水溶液中，Glyph 从其膦酸酯两性离子单体形式 (ZP) 二聚的机制可以通过一组包括直接质子转移路径的平衡来描述，如下所示： 2ZP 地平线 交流电 DZC。根据我们的结果，在水溶液中，DZC Glyph 二聚体及其相应的 DZP 和 AC 互变异构体应以比高 Glyph 浓度的膦酸两性离子 Glyph 单体更高的浓度存在，这一事实在文献中似乎存在争议。
更新日期：2024-07-23
AC DZC. Results show that solvents play a key role in modulating the energetics of the dimerization process of Glyph. Solvation in cyclohexane, favors the dimerization process however, hydration opposed it. In aqueous solution, the mechanism of the dimerization of Glyph from its phosphonate zwitterionic monomer form (ZP) could be described by a set of equilibria including direct proton transfer paths as follows: 2ZP DZP AC DZC. According to our results, in aqueous solution, DZC Glyph dimers and their corresponding DZP and AC tautomers should be present in higher concentration than phosphonate zwitterionic Glyph monomers for high Glyph concentration, a fact that seems controversial in the literature.
中文翻译：
草甘膦二聚化的计算研究：机理和溶剂的影响
通过量子化学方法对不同系列的草甘膦（Glyph）二聚体（包括中性单体的非离子化（N）和两性离子结构（Z））的结构和稳定性进行了计算研究，随后对 Glyph 二聚过程进行了能量学分析不同介质中的计算。作为 B3LYP-D3/6-311++G(2d,2p) 水平上介质的函数，计算了能量最小值的优化几何形状，以及每个系列 Glyph 二聚体可能的各种构象异构体的相对势和自由能。所有溶液相计算均采用基于密度（SMD）的溶剂化模型。非离子化二聚体 (DN)、阴离子-阳离子 (AC) 和两性离子-两性离子（DZP 和 DZC）或非离子化磷酸两性离子 (NZP) 电离中性形式的 Glyph 二聚体预计存在于气相和与 Glyph 单体形成鲜明对比的解决方案。发现两个羧酸盐两性离子单元呈中心对称排列的 DZC 二聚体形式是所有介质中最稳定的二聚体结构。在水溶液中，DZP 和 AC 二聚体型结构通过水合显着稳定。已在气相和溶液中研究了 DZC、DZP 和 AC 二聚体型结构之间的互变异构现象。 DZC 型结构在水中比在气相和环己烷中更容易发生质子转移。中性离子化 Glyph 二聚体中的互变异构过程的机制通过两个直接质子转移路径进行：DZP
交流电 DZC。结果表明，溶剂在调节 Glyph 二聚过程的能量方面发挥着关键作用。环己烷中的溶剂化有利于二聚过程，但水合作用则相反。 在水溶液中，Glyph 从其膦酸酯两性离子单体形式 (ZP) 二聚的机制可以通过一组包括直接质子转移路径的平衡来描述，如下所示： 2ZP 地平线 交流电 DZC。根据我们的结果，在水溶液中，DZC Glyph 二聚体及其相应的 DZP 和 AC 互变异构体应以比高 Glyph 浓度的膦酸两性离子 Glyph 单体更高的浓度存在，这一事实在文献中似乎存在争议。
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