Selective oxidation of sulfonamide antibiotics by periodate: Unexpected intermolecular hydrogen bond and structural rearrangement trigger radical production mechanism.

Organic pollutants are rich in electrons and chemical energy, offering potential for in situ water self-purification. However, the inherent thermodynamic stability of pollutants often renders them inert, necessitating external energy activation to utilize these potential properties. This work presents that periodate (PI) triggers nitrogen-containing pharmaceuticals (e.g., sulfonamide antibiotics, SAs) to release stored energy and electrons, enabling rapid and selective oxidative self-purification. PI selectively degrades SAs with six-membered heterocyclic ring (kobs = 0.0805-0.2781 min-1) but shows negligible reactivity towards five-membered analogues. Surprisingly, the reactive radical species rather than conventional direct oxidation, played major roles in SAs degradation. Density functional theory (DFT) calculations indicate that the sulfonamide group thermodynamically favors binding affinity toward PI, with in situ spectroscopy further verifying the formation of intermolecular hydrogen bond (O-H···N). Hydrogen bond-mediated electron transfer (HBET) triggers PI activation and structural rearrangement of SAs. However, five-membered heterocyclic rings in SAs adopt envelope conformations with angular deviation from ideal sp2 hybridization, inducing ring strain and geometric distortion that impedes PI attack. Transformation product analysis revealed that PI-induced oxidation proceeded through SO2 extrusion, hydroxylation, and coupling reaction. The practical applicability was demonstrated by its robust SAs removal (70-80 %) in real water matrices. Moreover, the generality of this process was validated across diverse nitrogen-containing pharmaceuticals, highlighting its treatment potential for prevalent contaminants. This work fills a critical knowledge gap on PI-induced oxidation mechanism, and demonstrates pollutant energy-driven water self-purification.