Dept. of Chemical Engineering, Columbia University, New York, NY, USA 10027.
Environ Sci Process Impacts. 2014 Apr;16(4):741-7. doi: 10.1039/c3em00579h.
Aqueous-phase reactions of organic compounds are of general importance in environmental systems. Reactions of α-dicarbonyl compounds in the aqueous phase of atmospheric aerosols can impact their climate-relevant physical properties including hygroscopicity and absorption of light. Less-reactive water-soluble organic compounds may contribute an organic matrix component to the aqueous environment, potentially impacting the reaction kinetics. In this work we demonstrate the effects of organic matrices on the self-reactions of glyoxal (Gly) and methylglyoxal (mGly) in aqueous solutions containing ammonium sulfate. At an organic-to-sulfate mass ratio of 2 : 1, carbohydrate-like matrices resembling oxidized organic aerosol material reduce the rate of formation of light-absorbing products by up to an order of magnitude. The greatest decreases in the reaction rates were observed for organic matrices with smaller, more linear molecular structures. Initial UV-Vis spectra, product studies, relative rate data, acidity changes, and viscosity measurements suggest that shifts in carbonyl equilibria, due in part to (hemi)acetal formation with the matrix, reduce the rate of formation of light-absorbing imidazole and oligomer species.
有机化合物的水相反应在环境系统中具有普遍意义。大气气溶胶水相中α-二羰基化合物的反应可以影响它们与气候相关的物理性质，包括吸湿性和对光的吸收。反应性较低的水溶性有机化合物可能会为水相环境提供有机基质成分，从而潜在地影响反应动力学。在这项工作中，我们证明了有机基质对含硫酸铵水溶液中乙二醛（Gly）和甲基乙二醛（mGly）自反应的影响。在有机-硫酸盐质量比为 2：1 时，类似于氧化有机气溶胶物质的碳水化合物样基质将光吸收产物的形成速率降低了一个数量级。对于具有较小、更线性分子结构的有机基质，反应速率的降低最大。初始 UV-Vis 光谱、产物研究、相对速率数据、酸度变化和粘度测量表明，由于与基质形成（半）缩醛，部分羰基平衡的转变降低了光吸收咪唑和低聚物形成的速率。
