Proton-Transfer Isomerization Driven by Strong Electric Fields in Aqueous Microdroplets

Proton-transfer isomerization is a fundamental process in chemistry, drug development, and materials science. External electric fields can serve as a powerful driving force for such isomerization, yet conventional approaches to generating strong fields are often limited by poor stability and demanding operational conditions. Here, we demonstrate that the spontaneously generated strong electric fields at the interface of aqueous microdroplets can efficiently drive the proton-transfer isomerization of 2,5-diamino-1,4-benzoquinone (DABQ). Combining mass spectrometry (MS), surface-enhanced Raman spectroscopy (SERS), ultraviolet-visible (UV-vis) absorption spectroscopy and density functional theory (DFT) calculations, we show that the isomerization proceeds via a water-assisted proton transfer pathway that concurrently converts the keto-enol and enamine-imine isomers. By tuning the interfacial electric field strength, the direction of the isomerization equilibrium and the distribution of individual isomers can be precisely controlled. Furthermore, we find that the environmental pollutant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q), which possesses a similar molecular backbone, also undergoes spontaneous isomerization in microdroplets, resulting in a significant reduction of its ecological toxicity across multiple trophic levels. This work establishes a novel platform for studying and controlling proton-transfer isomerization and offers a promising strategy for mitigating the toxicity of environmental pollutants.