Deal Alexandra M, Vaida Veronica
Department of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, United States.
Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado 80309, United States.
J Phys Chem A. 2023 Apr 6;127(13):2936-2945. doi: 10.1021/acs.jpca.3c00992. Epub 2023 Mar 24.
Lactic acid, a small α-hydroxyacid, is ubiquitous in both indoor and outdoor environments. Recently, the photochemistry of lactic acid has garnered interest among the abiotic organic chemistry community as it would have been present in abiotic settings and photoactive with the high-energy solar radiation that would have been available in the low oxygen early Earth environment. Additionally, we propose that the photochemistry of lactic acid is relevant to modern Earth during indoor ultraviolet-C (UVC) sterilization procedures as lactic acid is emitted by humans and is thus prevalent in indoor environments where UVC sterilization is increasingly being used. Here, we study the oxygen effect on the gas phase photolysis of lactic acid using Fourier-transform infrared (FTIR) spectroscopy and isotopically labeled oxygen (O). We find that the major products of gas phase lactic acid photolysis are CO, CO, acetaldehyde, and acetic acid. Furthermore, these products are the same with or without added oxygen, but the partial pressures of produced CO, CO, and acetaldehyde increase with the amount of added oxygen. Notably, the added oxygen is primarily incorporated into produced CO and CO, while little or none is incorporated into acetaldehyde. We combine the results presented here with those in the literature to propose a mechanism for the gas phase photolysis of lactic acid and the role of oxygen in this mechanism. Finally, we compare the output of a krypton-chloride excimer lamp (λ = 222 nm), one of the lamps proposed for UVC sterilization procedures, to the absorption of lactic acid. We show that lactic acid would be photoactive during UVC sterilization procedures, and we use the gas phase results presented here and aqueous lactic acid photolysis results previously published to assess potential byproducts from lactic acid reactions during UVC sterilization procedures.
乳酸是一种小分子α-羟基酸，在室内和室外环境中都普遍存在。最近，乳酸的光化学引起了非生物有机化学界的关注，因为它可能存在于非生物环境中，并且在早期地球低氧环境中可获得的高能太阳辐射下具有光活性。此外，我们认为乳酸的光化学与现代地球在室内紫外线-C（UVC）杀菌过程中相关，因为乳酸由人类排放，因此在越来越多地使用UVC杀菌的室内环境中普遍存在。在这里，我们使用傅里叶变换红外（FTIR）光谱和同位素标记的氧（O）研究了氧对乳酸气相光解的影响。我们发现乳酸气相光解的主要产物是CO、CO、乙醛和乙酸。此外，无论是否添加氧气，这些产物都是相同的，但生成的CO、CO和乙醛的分压会随着添加氧气量的增加而增加。值得注意的是，添加的氧主要结合到生成的CO和CO中，而很少或没有结合到乙醛中。我们将这里呈现的结果与文献中的结果相结合，提出了乳酸气相光解的机制以及氧在该机制中的作用。最后，我们将用于UVC杀菌过程的灯之一氪氯准分子灯（λ = 222 nm）的输出与乳酸的吸收进行了比较。我们表明乳酸在UVC杀菌过程中具有光活性，并且我们使用这里呈现的气相结果和先前发表的乳酸水溶液光解结果来评估UVC杀菌过程中乳酸反应的潜在副产物。
