Regulating CO and CC reduction by positively charged ions in water microdroplets

The fine-tuning of reactions in water microdroplets remains elusive. This study demonstrated that trace amounts of positively charged inorganic salts and organic compounds promoted the C O bond reduction of oxaloacetate while inhibiting the C C bond reduction of fumarate within water microdroplets. Similar effects were observed for carbonylated molecules with varying carbon chain lengths. Unlike conventional aqueous solutions requiring millimolar dopant concentrations, dopant levels as low as 10 nM in microdroplets were sufficient to induce these selective promotion and inhibition effects. A potential mechanism involving electrostatic interactions suggested that trace positively charged dopants drove the migration of carboxylated molecules from the microdroplet surface toward its interior. This relocation correlated with the changes in reaction reactivity. These findings could offer a novel approach to mediating reaction selectivity in microdroplets and have broad implications for atmospheric chemistry, chemical synthesis, and prebiotic processes where microdroplets interact with diverse surrounding substances.