A Molecular Dynamic Study of the Effects of Surface Partitioning on the OH Radical Interactions with Solutes in Multicomponent Aqueous Aerosols
A Molecular Dynamic Study of the Effects of Surface Partitioning on the OH Radical Interactions with Solutes in Multicomponent Aqueous Aerosols
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DOI：
10.1021/acs.jpca.2c07419
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发表时间：
2023-01-13
影响因子：
2.9
通讯作者：
Goulay，Fabien
中科院分区：
文献类型：
--
作者：
Masaya，Tadini Wenyika;Goulay，Fabien
用分子动力学方法研究了小分子糖和酰胺在水滴中的表面体积分配。空气-颗粒界面是用一个80 Å立方的水盒来模拟的，水盒中含有一系列有机分子，并被气态OH自由基包围。利用密度剖面和径向对分布函数在分子水平上考察了界面内有机溶质的性质和水的体积。只含有极性官能团的分子，如尿素和葡萄糖，主要存在于水中，在水面附近形成一个排斥层。糖和酰胺中单极基团被烷基取代导致分子向界面迁移。在距离水面2纳米的范围内，表面活性溶质失去旋转自由，并采用烷基指向表面的首选取向。界面内不同的填充导致了不同的溶剂化壳结构，并增强了有机分子与吸收OH自由基之间的相互作用。模拟提供了有关空气-水界面的尺寸、组成和组织的定量信息，以及OH自由基与有机溶质的非反应性相互作用。这表明，空气-水表面附近浓度的增加、择优取向和溶剂化程度的降低可能导致表面活性分子和表面非活性分子之间的反应性差异。这些结果对于解释界面内的非均相氧化机制和动力学如何可能与本体不同是很重要的。
The surface–bulk partitioning of small saccharide and amide molecules in aqueous droplets was investigated using molecular dynamics. The air–particle interface was modeled using a 80 Å cubic water box containing a series of organic molecules and surrounded by gaseous OH radicals. The properties of the organic solutes within the interface and the water bulk were examined at a molecular level using density profiles and radial pair distribution functions. Molecules containing only polar functional groups such as urea and glucose are found predominantly in the water bulk, forming an exclusion layer near the water surface. Substitution of a single polar group by an alkyl group in sugars and amides leads to the migration of the molecule toward the interface. Within the first 2 nm from the water surface, surface-active solutes lose their rotational freedom and adopt a preferred orientation with the alkyl group pointing toward the surface. The different packing within the interface leads to different solvation shell structures and enhanced interaction between the organic molecules and absorbed OH radicals. The simulations provide quantitative information about the dimension, composition, and organization of the air–water interface as well as about the nonreactive interaction of the OH radicals with the organic solutes. It suggests that increased concentrations, preferred orientations, and decreased solvation near the air–water surface may lead to differences in reactivities between surface-active and surface-inactive molecules. The results are important to explain how heterogeneous oxidation mechanisms and kinetics within interfaces may differ from those of the bulk.