Comparative in vitro and DFT antioxidant studies of phenolic group substituted pyridine-based azo derivatives

Two azo compounds 2-(3-pyridylazo)-3,5-dihydroxybenzoic acid (PAB) and 4-(3-pyridylazo)resorcinol (PAR) thought to have the potential to be used as antioxidants were designed, synthesized and antioxidant activities were investigated both in vitro and in silico. The synthesized compounds were characterized by H-1-NMR, C-13-NMR, FT-IR, UV-Vis and mass spectra. The molecular geometry and vibrational frequency calculations of the synthesized compounds in ground state were performed by the density functional theory (DFT) employing B3LYP level with the 6-311 G(d,p) basis set. The gauge independent atomic orbital (GIAO) method was used to determine the chemical shift values of H-1-NMR and C-13-NMR. HOMO-LUMO calculations were carried out by time-dependent DFT (TD-DFT) approach. Computational spectroscopic data of the synthesized compounds are fully compatible with experimental ones. The antioxidant activities of the PAB and PAR were investigated by using DPPH assay. It was determined that the PAB molecule showed better antioxidant activity than PAR and, butylated hydroxytoluene (BHT) which is the standard antioxidant. In addition, the thermodynamic stability parameters obtained with the help of DFT calculations were found to be quite compatible with the antioxidant capacity sequence derived from the DPPH assay.

Automated summary

In this study, two azo compounds, PAB and PAR, were designed and synthesized for their potential use as antioxidants. Antioxidant activities of these compounds were investigated both experimentally and computationally. The results showed that PAB had better antioxidant activity compared to PAR and BHT. The computational data were in good agreement with the experimental results, confirming their reliability.