DFT study of free radical scavenging mechanisms in UiO-66-(OH)2 and UiO-66-NH2 MOFs

Abstract

This study employs density functional theory (DFT) to investigate three common free radical scavenging mechanisms (hydrogen atom transfer (HAT), single electron transfer proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET)) in UiO-66-(OH)₂ and UiO-66-NH₂ metal–organic framework (MOF) nanoparticles under gas, benzene and aqueous phase conditions. The reaction processes between UiO-66-(OH)₂/UiO-66-NH₂ and hydroxyl radicals (˙OH) were simulated to elucidate detailed radical capture pathways, and the computational results were validated by macroscopic DPPH radical scavenging experiments. The results indicate that: (1) among the three mechanisms, HAT consistently exhibits the lowest bond dissociation energy across all phases, suggesting MOF nanoparticles preferentially undergo hydrogen atom transfer over electron transfer during radical scavenging; (2) compared to gas phase and nonpolar solvent (benzene), polar solvent (water) significantly lowers the energy barriers for both electron transfer and hydrogen transfer, thus enhancing reactivity across all mechanisms; (3) UiO-66-(OH)₂ exhibits a radical scavenging rate constant of 1.0 × 10⁹ M⁻¹ s⁻¹, higher than 7.63 × 10⁸ M⁻¹ s⁻¹ for UiO-66-NH₂; (4) DPPH assays reveal that UiO-66-(OH)₂ exhibits an 8% greater radical scavenging efficiency than UiO-66-NH₂, in agreement with DFT predictions and confirming the antioxidative benefit of hydroxyl functionalization. This study proposes a combined DFT and experimental screening workflow for radical scavengers, offering an efficient and economical approach to rapidly identify novel MOF-based radioprotective radical scavengers.