Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China.
J Phys Chem A. 2020 Dec 10;124(49):10246-10257. doi: 10.1021/acs.jpca.0c07908. Epub 2020 Nov 25.
Atmospheric amines are thought to play significant roles in the nucleation of sulfuric acid-mediated aerosol particles. Their enhancing effects on the stabilization of the related complexes have formerly been correlated with the amine base strength, but there are a few exceptions reported. In this work, the influence of seven alkylamines on the thermodynamic stability of sulfuric acid-amine complexes has been theoretically investigated, e.g., ethylamine, propylamine, isopropylamine, -butylamine, dimethylamine, ethylmethylamine, and trimethylamine. For all primary and secondary amine-mediated complexes, a dual hydrogen bond configuration is generally suggested in the most stable isomer. The stabilization of this special structure predicted by the electrostatic potential distribution on the molecular surface of amines exactly agrees with the base strength sequence, providing crucial evidence for the previous deduction of correlation between the base strength and the enhancing effect. Meanwhile, the considerable van der Waals interactions are found between the free hydroxyl of sulfuric acid and the β-methyl group of amine, resulting in the extra stability for sulfuric acid-dimethylamine and sulfuric acid-ethylmethylamine complexes. Therefore, the electrostatic potential distribution of amines is the essential determinant factor for the thermodynamic stability of the relevant complexes. Our conclusions provide new insight into a way to evaluate the enhancing abilities of amines in aerosol particle nucleation.
大气胺被认为在硫酸介导的气溶胶粒子成核中起着重要作用。它们对相关配合物稳定性的增强作用以前与胺碱强度有关，但也有一些例外报告。在这项工作中，理论上研究了七种烷基胺对硫酸-胺配合物热力学稳定性的影响，例如乙胺、丙胺、异丙胺、-丁胺、二甲胺、乙甲基胺和三甲胺。对于所有伯胺和仲胺介导的配合物，最稳定的异构体中通常建议采用双氢键构型。静电势能在胺分子表面上的分布准确预测了这种特殊结构的稳定性，与碱强度序列完全一致，为以前关于碱强度与增强效应之间相关性的推论提供了重要证据。同时，在硫酸和胺的自由羟基之间发现了相当大的范德华相互作用，导致硫酸二甲胺和硫酸乙甲基胺配合物的额外稳定性。因此，胺的静电势能分布是相关配合物热力学稳定性的决定因素。我们的结论为评估胺在气溶胶粒子成核中增强能力的方法提供了新的见解。
