Molecular Modeling of the Green Leaf Volatile Methyl Salicylate on Atmospheric Air/Water Interfaces
Molecular Modeling of the Green Leaf Volatile Methyl Salicylate on Atmospheric Air/Water Interfaces
复制标题
DOI：
10.1021/jp4029694
复制
发表时间：
2013-05-30
影响因子：
2.9
通讯作者：
Hung, Francisco R.
中科院分区：
文献类型：
--
作者：
Liyana-Arachchi, Thilanga P.;Hansel, Arnie K.;Hung, Francisco R.
水杨酸甲酯 (MeSA) 是一种绿叶挥发性 (GLV) 化合物，植物会大量排放，尤其是在胁迫条件下。然后，GLV 可以与大气中的氧化剂发生化学反应，产生有助于形成二次有机气溶胶 (SOA) 的化合物。我们使用热力学积分 (TI)、平均力势 (PMF) 计算和经典分子动力学 (MD) 模拟研究了 298 K 下 MeSA 在大气空气/水界面上的吸附。我们的分子模型可以重现 MeSA 1-辛醇/水分配系数的实验结果。在空气/水界面处发现了 MeSA 的深层自由能最小值，这主要是由 MeSA 和水之间的能量相互作用驱动的。在界面处，MeSA 中的含氧基团倾向于指向界面的水侧，而 MeSA 的芳香基团则远离水。 MeSA 浓度的增加导致 MeSA-MeSA g(r) 函数中峰高度的降低，界面处 MeSA 和水动力学的减慢以及界面表面张力的降低。我们的结果表明，MeSA 具有强烈的热力学偏好，倾向于保留在空气/水界面，因此与大气氧化剂的化学反应更有可能发生在该界面，而不是在大气水滴的水相或气相中。
Methyl salicylate (MeSA) is a green leaf volatile (GLV) compound that is emitted in significant amounts by plants, especially when they are under stress conditions. GLVs can then undergo chemical reactions with atmospheric oxidants, yielding compounds that contribute to the formation of secondary organic aerosols (SOAs). We investigated the adsorption of MeSA on atmospheric air/water interfaces at 298 K using thermodynamic integration (TI), potential of mean force (PMF) calculations, and classical molecular dynamics (MD) simulations. Our molecular models can reproduce experimental results of the 1-octanol/water partition coefficient of MeSA. A deep free energy minimum was found for MeSA at the air/water interface, which is mainly driven by energetic interactions between MeSA and water. At the interface, the oxygenated groups in MeSA tend to point toward the water side of the interface, with the aromatic group of MeSA lying farther away from water. Increases in the concentrations of MeSA lead to reductions in the height of the peaks in the MeSA-MeSA g(r) functions, a slowing down of the dynamics of both MeSA and water at the interface, and a reduction in the interfacial surface tension. Our results indicate that MeSA has a strong thermodynamic preference to remain at the air/water interface, and thus chemical reactions with atmospheric oxidants are more likely to take place at this interface, rather than in the water phase of atmospheric water droplets or in the gas phase.