In this work, the density functional theory method were used to investigate the ground state energies, spin density, atomic charge distribution, HOMO-LUMO gap, O-H bond dissociation enthalpies (BDEs) and ionization potential (IP) of the glycyrrhizic acid (GL) and its monolithium, monosodium, monopotassium and monoammonium salts in the gas phase. The results show that there is a clear correlation between O-H BDE and the spin density and the atomic charges. The more delocalized spin density in the radicals and the higher atomic charges of remaining O-atoms after H-removal is equivalent to the lower BDE and higher antioxidant character in H-atom transfer mechanism. The obtained values for the IP indicate that the lowest IP having the lowest HOMO-LUMO gap (E). Nevertheless, the trend of the IP cannot be interpreted only on the basis of the E. However; the inclusion of Li, Na, K and NH3 improved the stability of GL molecule and all of the radicals. We believe that the obtained results may be helpful in the field of biological antioxidant study.
