Wilhelm-Ostwald Institut für Physikalische und Theoretische Chemie, University of Leipzig, Linnéstrasse. 2, D-04103, Leipzig, Germany.
J Chem Phys. 2010 Mar 28;132(12):124506. doi: 10.1063/1.3354108.
The dynamics of the protic ionic liquid monomethylammonium nitrate is investigated by Car-Parrinello molecular dynamics simulations. On average, 1.8 of 3 possible hydrogen bond contacts are formed. Therefore, one hydrogen bond acceptor and one donor site in each ion pair of monomethylammonium nitrate remains free, which is similar to water. Furthermore, like water, monomethylammonium nitrate exhibits a fast fluctuating hydrogen bond network. The comparable hydrogen bond network and dynamics of both liquids might explain the similar impact on reactivity and selectivity found for chemical reactions. However, the hydrogen bond network of monomethylammonium nitrate and water show some structural differences. While the hydrogen bonds in water arrange in parallel fashion, the hydrogen bonds of monomethylammonium nitrate prefer angles of 0 degrees, 90 degrees, and 180 degrees. The ion dynamics of monomethylammonium nitrate indicate that at about 85% of the ion pairs are still connected after 14.5 ps. A closer inspection of the first solvation shell dynamics of one cation reveals that after 11 ps the current ion pair conformation is independent of the initial ion pair conformation because the ion pairs lose their information of the initial ion pair conformation much faster than the time needed to escape from their solvent cage. The ion dynamics of monomethylammonium nitrate can be described by the following model: There are ions rattling in long living cages which are formed by long living ion pairs.
通过 Car-Parrinello 分子动力学模拟研究了质子离子液体硝酸甲铵的动力学。平均而言，在 3 个可能的氢键接触中有 1.8 个形成。因此，硝酸甲铵的每个离子对中仍有一个氢键受体和一个供体位点是自由的，这与水类似。此外，与水一样，硝酸甲铵也表现出快速波动的氢键网络。这两种液体相似的氢键网络和动力学可能解释了化学反应中发现的类似反应性和选择性的影响。然而，硝酸甲铵和水的氢键网络显示出一些结构差异。虽然水中的氢键呈平行排列，但硝酸甲铵的氢键更喜欢 0 度、90 度和 180 度的角度。硝酸甲铵的离子动力学表明，在大约 14.5 ps 后，约 85%的离子对仍然相连。对一个阳离子的第一溶剂化壳动力学的更仔细研究表明，在 11 ps 后，当前离子对构象与初始离子对构象无关，因为离子对失去初始离子对构象的信息速度比它们从溶剂笼中逃逸所需的时间快得多。硝酸甲铵的离子动力学可以用以下模型来描述：有离子在长寿命的笼子里嘎嘎作响，这些笼子是由长寿命的离子对形成的。
