Benzofuran-stilbene hybrid compounds: an antioxidant assessment - a DFT study

The antioxidative activities of the original compound dehydro-δ-viniferin ( 1 ) and its three designated derivatives, 5-(2-(4-hydroxyphenyl)benzofuran-3-yl)benzene-1,3-diol ( 2 ), ( E )-5-(2-(2-(4-hydroxyphenyl)benzofuran-5-yl)vinyl)benzene-1,3-diol ( 3 ), and ( E )-5-(2-(3-(3,5-dihydroxyphenyl)benzofuran-5-yl)vinyl)benzene-1,3-diol ( 4 ), are extensively studied, mainly based on density functional theory (DFT) calculations using the hybrid functional B3LYP and the 6-311G(d,p) basis set. The O-H bond breakage is reasonably responsible for the antioxidative activity, whereas the environment greatly influences results. In solvents, namely water, methanol, and especially acetone, the SPL-ET mechanism (sequential proton loss-electron transfer) is mainly likely to be a antioxidative route for four studied compounds; however, the HAT mechanism (hydrogen atom transfer) is assigned to these compounds in the gaseous phase. Benzofuran-stilbene hybrid compound 3 with a planar structure is the best antioxidative agent; its 4′-OH induced the lowest PA values in liquid solvents as well as the lowest BDE value in the gas solvent. The kinetic investigation of the interactions of compounds 1-4 with HOO&z.rad; radicals evidently provides the lowest Gibbs activation energy Δ G # = 4.7 kcal mol −1 and the highest rate constant K = 5.702 × 10 10 L mol −1 s −1 , which again are assigned to 3 -4′-OH. At the theoretical level of B3LYP/6-311G(d,p)/LANL2DZ, the complex [La(compound 3 ) 3 ] in gas induces a redshift in the UV-Vis spectrum. The kinetic reaction of the benzofuran-stilbene hybrid compound 5-(2-(2-(4-hydroxyphenyl)benzofuran-5-yl)vinyl)benzene-1,3-diol captures the HOO&z.rad; free radical.