The antioxidant power of quercetin-3-O-glucuronide (miquelianin) has been studied, at the density functional level of theory, in both lipid-like and aqueous environments. In the aqueous phase, the computed pKa equilibria allows the identification of the neutral and charged species present in solution that can react with the •OOH radical. The Hydrogen Atom Transfer (HAT), Single Electron Transfer (SET) and Radical Adduct Formation (RAF) mechanisms were considered and the individual, total and fraction corrected total rate constants were obtained. Potential non covalent inhibition of Mpro from SARS-CoV-2 by miquelianin has been also been evaluated.