Rapf Rebecca J, Perkins Russell J, Carpenter Barry K, Vaida Veronica
Department of Chemistry and Biochemistry and Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder , Boulder, Colorado 80309, United States.
School of Chemistry and the Physical Organic Chemistry Centre, Cardiff University , Cardiff CF10 3AT, United Kingdom.
J Phys Chem A. 2017 Jun 8;121(22):4272-4282. doi: 10.1021/acs.jpca.7b03310. Epub 2017 May 30.
The aqueous phase photochemistry of pyruvic acid, an important oxidation product of isoprene, is known to generate larger oligomeric species that may contribute to the formation of secondary organic aerosol in the atmosphere. Using high resolution negative mode electrospray ionization mass spectrometry, the aqueous photochemistry of dilute solutions of pyruvic acid (10, 1, and 0.5 mM) under anaerobic conditions was investigated. Even at the lowest concentration, covalently bonded dimers and trimers of pyruvic acid were observed as photochemical products. We calculate that it is energetically possible to photochemically generate parapyruvic acid, a dimer of pyruvic acid that is known to form via dark oligomerization processes. Subsequent photochemical reactions of parapyruvic acid with pyruvic acid form larger oligomeric products, such as 2,4-dihydroxy-2-methyl-5-oxohexanoic acid. A robust and relatively simple photochemical mechanism is discussed that explains both the conditional dependence and wide array of products that are observed.
丙酮酸是异戊二烯的一种重要氧化产物，其水相光化学过程会生成较大的低聚体物种，这些物种可能有助于大气中二次有机气溶胶的形成。利用高分辨率负模式电喷雾电离质谱，对厌氧条件下丙酮酸稀溶液（10 mM、1 mM和0.5 mM）的水相光化学进行了研究。即使在最低浓度下，也观察到丙酮酸的共价键二聚体和三聚体作为光化学产物。我们计算得出，光化学生成副丙酮酸在能量上是可能的，副丙酮酸是丙酮酸的一种二聚体，已知其可通过暗聚过程形成。副丙酮酸与丙酮酸随后的光化学反应会形成更大的低聚产物，如2,4 - 二羟基 - 2 - 甲基 - 5 - 氧代己酸。本文讨论了一个稳健且相对简单的光化学机制，该机制解释了所观察到的条件依赖性和广泛的产物种类。
