Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, P.O. Box 34110, Doha, Qatar.
Department of Earth and Environmental Science and Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
J Chem Phys. 2020 Apr 30;152(16):164702. doi: 10.1063/1.5143402.
We present results from molecular dynamics simulations coupled with enhanced sampling techniques on the adsorption and isomerization of glyoxal (GL) and methylglyoxal (MG) at the air/hydroxylated silica (α-Quartz) interface. GL and MG are two organic compounds present in the atmosphere as oxidation products of both biogenic and anthropogenic precursors. By adsorption and hydration on liquid droplets or wetted dust particles, they can enable aerosol growth in the atmosphere. Moreover, thanks to the different polar characters of their trans and cis conformers, GL and MG have been suggested as possible molecular switches capable of responding to changes in solvent polarity. Here, we show that the hydroxylated silica surface does not significantly catalyze the trans-to-cis isomerization, but it stabilizes the cis-isomers, indicating a higher interfacial cis/trans relative concentration compared to the gas phase. Moreover, adsorbed GL prefers to lie parallel on the silica surface, while adsorbed MG shows a tilted orientation. In particular, we report the aldehyde group pointing upward (downward) to the gas phase (to the silica surface) in trans-MG (cis-MG). These results will help in the rationalization of upcoming experimental and modeling work on the adsorption of ketonic compounds on dust aerosols, while it clarifies the catalytic role of the solid substrate surface in promoting conformational changes.
我们呈现了分子动力学模拟与增强采样技术相结合的结果，这些结果涉及到在空气/水合二氧化硅（α-石英）界面上的乙二醛（GL）和甲基乙二醛（MG）的吸附和异构化。GL 和 MG 是两种存在于大气中的有机化合物，它们是生物和人为前体氧化的产物。通过在液滴或湿尘粒子上的吸附和水合作用，它们可以促进大气中的气溶胶生长。此外，由于其反式和顺式构象的不同极性特征，GL 和 MG 已被提议为可能的分子开关，能够响应溶剂极性的变化。在这里，我们表明，水合二氧化硅表面不会显著催化反式到顺式的异构化，但它稳定了顺式异构体，表明与气相相比，界面上的顺式/反式相对浓度更高。此外，吸附的 GL 更喜欢平行于二氧化硅表面，而吸附的 MG 则呈现出倾斜的取向。特别是，我们报告了反式-MG（顺式-MG）中醛基指向气相（指向二氧化硅表面）。这些结果将有助于对酮类化合物在尘埃气溶胶上吸附的后续实验和建模工作的合理化，同时阐明了固体基底表面在促进构象变化方面的催化作用。
