Formation of 2,4–D complexes on montmorillonites – an ab initio molecular dynamics study
Formation of 2,4–D complexes on montmorillonites – an ab initio molecular dynamics study
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DOI：
10.1111/j.1365-2389.2006.00853.x
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发表时间：
2007-06
影响因子：
4.2
通讯作者：
D. Tunega;M. Gerzabek;G. Haberhauer;H. Lischka
中科院分区：
文献类型：
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作者：
D. Tunega;M. Gerzabek;G. Haberhauer;H. Lischka
在室温下，采用短时间从头算分子动力学（MD）模拟研究了阴离子形式的农药2，4-D（2，4-二氯苯氧乙酸）在粘土矿物蒙脱石表面的吸附。三种不同的情况进行了建模：吸附在干燥的表面上，在水合表面和蒙脱石层之间的插层。在所有三种情况下，钙阳离子补偿蒙脱石层的过量负电荷和2，4-D阴离子的负电荷。结果表明，在所有的模型与钙离子直接接触的蒙脱石层，钙离子的最稳定的位置是上方的双三角孔的矿物层。虽然在干燥表面的情况下，在2，4-D阴离子和Ca 2+阳离子之间产生非常稳定的双齿结合，但在包括水分子的所有模型中优选形成单齿络合物。水分子与2，4-D阴离子之间形成的氢键对单齿配合物的形成有相当大的贡献。蒙脱石层中的四面体取代对任何类型的复合物的形成都有显着的影响。然而，分子动力学模拟不支持的作用，钙离子作为阳离子桥的吸附机制。计算表明，水合2，4-D···Ca ~（2+）复合物比Ca ~（2+）阳离子作为表面桥的复合物更稳定。另一方面，具有更大浓度的同晶取代的页硅酸盐（例如云母）将能够形成具有阳离子桥机制的稳定的表面络合物。
Sorption of the anionic form of the pesticide 2,4–D (2,4–dichlorophenoxyacetic acid) on the surface of the clay mineral montmorillonite was investigated using a short‐time ab initio molecular dynamics (MD) simulation at room temperature. Three different situations were modelled: sorption on a dry surface, on a hydrated surface and an intercalation between montmorillonite layers. In all three cases, the calcium cation compensates the excess negative charge of the montmorillonite layer and the negative charge of the 2,4–D anion. It was found that in all models with direct contact of the Ca2+ cation with the montmorillonite layer, the most stable position of Ca2+ is above the ditrigonal hole of the mineral layer. While in the case of a dry surface very stable bidentate binding is created between the 2,4–D anion and the Ca2+ cation, the formation of the monodentate complexes is preferred in all models that include water molecules. Hydrogen bonds formed between water molecules and the 2,4–D anion make a considerable contribution to the formation of the monodentate complexes. Tetrahedral substitutions in the montmorillonite layer have a significant effect on the formation of the complexes of any type. However, the MD simulations did not support the role of Ca2+ as a cation bridge in the adsorption mechanism. Calculations showed that hydrated 2,4–D···Ca2+ complexes are thermodynamically more stable than complexes in which the Ca2+ cation acts as a bridge to the surface. On the other hand, it is possible that phyllosilicates with a greater concentration of isomorphic substitutions (e.g. mica) will be able to form stable surface complexes with a cation bridge mechanism.