A DFT study on the radical scavenging potential of selected natural 3′,4′-dihydroxy aurones

A series of 3′,4′-dihydroxy natural aurones differing in ring A substitution pattern have been studied with regards to their radical scavenging potential in the gas and in the liquid phase (benzene, water) using density functional theory (DFT) and the Becke's 3 Lee Yang Parr functional (B3LYP). Based on O-H bond dissociation enthalpy (BDE) and adiabatic ionization potential (IP) values, all tested aurones are expected to be more efficient hydrogen atom and electron donors than luteolin. The substitution pattern in ring A may have an impact on hydrogen atom donating activity of the compounds as phenolic and non-phenolic hydrogen atoms may be donated. Substitution affected polarity and in certain cases planarity of compounds, which may influence efficiency in real systems. Hydration at C-2 (auronols) affected polarity, electron donation and stability of the derived phenoxy radical at C-4′ and loss of planarity, rendering membrane penetration difficult. Change in C ring configuration (isoaurones) resulted in lower IP and O-H BDE value at C-6. The current findings suggest that aurones deserve more attention for food or pharmaceutical applications as antioxidants.