Theoretical Study on The Investigation of Antioxidant Properties of Some 4-Benzylidenamino-4,5-dihydro-1H-1,2,4-triazol-5-one Derivatives

In this study, the antioxidant properties of some experimentally determined 4-benzylideneamino-4,5-dihydro-1H-1,2,4-triazol-5-one derivatives of antioxidant properties were compared by density functional theory method. Quantum chemical calculations based on density functional theory (DFT) were employed to study the relationship between 4-benzylideneamino-4,5-dihydro-1H-1,2,4-triazol-5-one derivatives (for 2a and 2g) having the highest and least antioxidant activity in experimental results. The solvation effects on the antioxidant activity were taken into account by using the conductor-like polarisable continuum model with different dielectric constants (？= 2.25, C6H6; ？ = 78.39, H2O). The three antioxidant action mechanisms, hydrogen atom transfer (HAT), single electron transfer-proton transfer (SET-PT) and sequential protonloss electron transfer (SPLET) were elucidated. The reaction enthalpies related to the steps in these mechanisms were computed in gas phase and solvents, the compatibility of the calculated results with experimental values is discussed. The results showed that SPLET was the most favourable mechanism for describing the antioxidant activity of 2a and 2g in the aqueous phase, SPLET represented the most thermodynamically plausible reaction pathway. Calculations performed by using DFT method at the rB3LYP/6-311++G (2d,2p) level of theory for neutral molecules and anions in the gas and solvation phase, for radicals and cations, uB3LYP/ 6-311++G (2d,2p) basis set has been used