Unveiling the multiphase fate of 2,4-dinitrophenol on aerosols: interfacial hydration modulates competing oxidation pathways and predicted toxicity indicators

This study elucidates the mechanisms of selected transformation pathways of 2,4-dinitrophenol (2,4-DNP) using an integrated computational framework. In the gas phase, the calculated initial reactions with hydroxyl radicals (⚫OH) and ozone (O ₃ ) are kinetically more favorable than the direct reaction with nitrogen dioxide radical (⚫NO ₂ ), which is kinetically hindered. In the aqueous phase, solvation substantially modifies the calculated reaction kinetics, and the cumulative electron-withdrawing effect of the two nitro substituents lowers the O ₃ reaction rate coefficient by approximately three orders of magnitude relative to mononitrocatechol. For the key radical intermediate generated by ⚫OH addition, hydrogen atom abstraction (HAA) by O ₂ is kinetically favored over the competing ⚫NO ₂ pathway based on the calculated barriers and an illustrative comparison of effective rates under representative atmospheric concentrations. At the gas-aqueous interface, molecular dynamics (MD) simulations show a non-monotonic dependence of 2,4-DNP adsorption on hydration in the idealized C60/water system, with adsorption strengthening at moderate hydration and weakening at high hydration. Finally, QSAR calculations predict that certain ozonolysis products exhibit higher predicted Ames mutagenicity and developmental toxicity indicators than the parent compound, indicating product-specific changes in predicted toxicity profiles during oxidation. These screening-level predictions require experimental validation. These findings provide molecular-level mechanistic insights into selected transformation pathways and interfacial interactions involving 2,4-DNP and motivate further experimental investigation of its transformation products and their toxicological properties.