Nandy Abhijit, Mondal Supratim, Koner Debasish, Banerjee Shibdas
Department of Chemistry, Indian Institute of Science Education and Research Tirupati, Tirupati 517507, India.
Department of Chemistry, Indian Institute of Technology Hyderabad, Kandi 502284, India.
J Am Chem Soc. 2024 Jul 17;146(28):19050-19058. doi: 10.1021/jacs.4c03315. Epub 2024 Jul 3.
Water microdroplets promote unusual chemical reactions at the air-water interface. However, the interfacial structure of water microdroplets and its potential influence on chemical processes are still enigmatic. Here, we present evidence of in-droplet fractionation of water isotopologues. Employing a sonic spray, we atomized the heavy water (DO, 99.9 atom % D) solution of three classes of organic compounds (basic, acidic, and neutral). The analytes were predominantly desorbed from the resulting droplet surface in protonated form rather than deuterated form, as detected by mass spectrometry. This result remained unaltered upon adding formic acid- (DCOOD) to the droplet. Monitoring Dakin oxidation of benzaldehyde at the surface of binary microdroplets composed of 1:1 (/) DO/HO revealed the preferred formation of phenolate-O over phenolate-O. Atmospheric pressure chemical ionization mass spectrometric analysis of the vapor composition in the sprayed aerosol revealed the preferential evaporation of lighter water isotopologue impurities from the surface of heavy water microdroplets. These results indicate the enrichment of lighter water isotopologue impurities (HOD/HO) on the surface of heavy water microdroplets, implying possible future developments for water isotopologue fractionation using microdroplets.
水微滴在气-水界面促进异常化学反应。然而，水微滴的界面结构及其对化学过程的潜在影响仍然是个谜。在此，我们展示了水同位素异构体在液滴内分馏的证据。利用超声喷雾，我们雾化了三类有机化合物（碱性、酸性和中性）的重水（D₂O，99.9原子%D）溶液。通过质谱检测发现，分析物主要以质子化形式而非氘代形式从所得液滴表面解吸。向液滴中添加甲酸-d（DCOOD）后，这一结果保持不变。监测由1:1（/）D₂O/H₂O组成的二元微滴表面苯甲醛的达金氧化反应，发现酚盐-O比酚盐-O更易形成。对喷雾气溶胶中蒸汽成分的大气压化学电离质谱分析表明，轻水同位素异构体杂质从重水微滴表面优先蒸发。这些结果表明轻水同位素异构体杂质（HOD/H₂O）在重水微滴表面富集，这意味着未来利用微滴进行水同位素异构体分馏可能有新的进展。
