Catalyst-Free Ammonia Formation at the Gas-Liquid Interface Enables Selective Nitrogen-Saccharide Association Under...

Ammonia (NH₃) is one of the quintessential building blocks in the renowned nitrogen cycle, which sustains life activities. Probing the abiotic formation of ammonia is vital to both understanding the prebiotic nitrogen incorporation, and exploring novel opportunities in its synthetic acquisition. Here, we report a catalyst-free process for in situ ammonia formation at the gas-liquid interface of aqueous microdroplets. Specifically, saccharide molecular-probe solution through dinitrogen nebulization generated saccharide-ammonium adducts [M+NH₄]⁺ in mass spectrometry detection that were absent under argon-mediated control experiments, while ion chromatography and UV-Vis spectroscopy independently verified ammonia generation exclusively in aqueous microdroplet. Quantitative isotope-dilution mass spectrometry determined an overall NH₃ formation rate of 8.35 × 10^-4 mg·h^-1 in the microdroplet spray region. Spin-trapping, electron paramagnetic resonance, radical-scavenging, and intermediate-derivatization experiments, supported by electric-field-assisted theoretical calculations, further indicate a hydrogen-radical-mediated, stepwise nitrogen hydrogenation pathway involving N₂H₄. Additionally, saccharides, decreasing microdroplet size enhances ammonium adduct formation while suppressing alkali-metal adducts, a trend rationalized by electric-field-dependent stabilization of [M+NH₄]⁺ over [M+Na]⁺ and [M+K]⁺, as supported by density functional theory calculations. These findings support a microdroplet-electric-field-driven ambient ammonia formation at the gas-liquid interfaces, and provide mechanistic insights into prebiotic nitrogen-saccharide association under abiotic conditions.