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

Abstract

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˙ radicals evidently provides the lowest Gibbs activation energy ΔG^# = 4.7 kcal mol⁻¹ and the highest rate constant K = 5.702 × 10¹⁰ 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.