Abstract
Twenty-nine ellagitannin derivatives and ellagic acid (EA) metabolites have been chosen to calculate the aqueous and DMSO acidity constants (pKa) and proton affinities (PA) as criterions for estimating antioxidant activity. The calculations have been performed using density functional theory (DFT) and MP2 methods in conjugation with SMD continuum model. The pKa values calculated with the MP2 method are in agreement with the experimental pKa values of EA with low percentage errors. The results show significant differences in the acidic content of several OH phenolic groups of each metabolite. A reliable relationship is observed between the pKa (also PA) values and the minimum of electrostatic potential (Vmin) in the vicinity of acidic sites. The OH group located at the position 5 of urolithin M5 (UM5) is the most acidic site through the effect of intramolecular hydrogen bonding. The glucuronide substituent increases the acidity of metabolites in water and DMSO solvents. Isourolithin A3-glucuronide is the most acidic metabolites among the methyl and glucuronide-conjugated metabolites in both solvents. According to the results, the EA metabolites are good lipophilic antioxidant, as well as EA itself.
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