Superoxide radical scavenging by sodium 4,5-dihydroxybenzene-1,3-disulfonate dissolved in water: Experimental and quantum chemical studies

Tiron (sodium 4,5-dihydroxybenzene-1,3-disulfonate) is often used as a probe for detection of superoxide radicals. In thiswork, we have studied the interaction of Tiron with superoxide radicals dissolved inwater solutions. The density functional theory (DFT) methodwas used for scrutinizing electron and energy characteristics of Tiron radicals in the systemsmodeling freshwater and saltwater. Inwater solution at neutral pH, deprotonated formof superoxide radical, O-2(center dot-), dominates over the protonated form HO2 center dot. Fully reduced (TH2) and fully oxidized (T) species of Tiron react with superoxide radicals, leading to the formation of the Tiron semiquinone radicals. DFT calculations show that the reactions of O-2(center dot-) with TH2 and T in water solution will advance if these reactions are catalyzed by hydronium ions: TH2+ O-2(center dot-) + H3O+ -> TH center dot + H2O2 + H2O and T + O-2(center dot-) + H3O+ -> TH center dot + O-2 + H2O. Electron paramagnetic resonance (EPR) and DFT data showthat Tiron radicals dissolved inwater solution with neutral pH exist predominantly in deprotonated state T center dot-. The constants of the hyperfine coupling between an unpaired electron and the hydrogen atoms of deprotonated radicals T center dot-, computed for freshwater and seawater solutions, are in a fairly good agreement with experimental constants derived from the EPR spectra of Tiron radicals. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Tiron is commonly used as a probe for detection of superoxide radicals. The interaction of Tiron with superoxide radicals dissolved in water solutions was studied using density functional theory (DFT) method. The reactions of Tiron with superoxide radicals are influenced by hydronium ions, leading to the formation of Tiron semiquinone radicals.