An experimental and DFT study on free radical scavenging activity of hesperetin Schiff bases

Three hesperetin Schiff bases N-[2,3-dihydro-5,7-dihydroxy-2-(3-hydroxy-4-methoxyphenyl)chromen-4-ylidene]thiosemicarbazide (HTSC), N-[2,3-dihydro-5,7-dihydroxy-2-(3-hydroxy-4-methoxyphenyl)chromen-4-ylidene]isonicotinohydrazide (HIN) and N-[2,3-dihydro-5,7-dihydroxy-2-(3-hydroxy-4-methoxy-phenyl)chromen-4-ylidene] benzhydrazide (HHSB) were synthesized and evaluated for their electronic and physicochemical properties using experimental and theoretical methods. In order to determine antioxidant activity of the above mentioned compounds a detailed kinetic study of hesperetin analogues has been performed and comprehensive results have been reported with DPPH center dot assay using UV-Vis and H-1 NMR spectroscopy. Using DPPH assay, the order of the antioxidant activity increase was established as HTSC > HIN > HHSB > hesperetin. Based on the theoretical DET(B3LYP) calculations it was concluded that in polar solvents (methanol and DMSO) the first step of free radical scavenging mechanism of hesperetin derivatives is deprotonation of the 7-OH groups leading to the formation of anionic forms. These anionic species are considered to be the entering species to the two coexisting or competing mechanisms: SPLET and SPL-HAT.