Antioxidant activity of thiourea derivatives: An experimental and theoretical study

Abstract Antioxidant ability of thiourea derivatives was characterized based on the measurement of the color change of 2,2-diphenyl-1-picrylhydrazyl (DPPH ) and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS +) when reacting with the studied compounds. The values of IC50DPPH/ [IC50ABTS] of DPTU (1,3-diphenyl-2-thiourea) and BPTU (1-benzyl-3-phenyl-2-thiourea) are of 0.710 ± 0.001 mM/[0.044 ± 0.001 mM] and 11.000 ± 0.015 mM/[2.400 ± 0.021 mM], respectively. As a result, it could be concluded that DPTU could capture free radicals better than BPTU and quantum chemical calculations also confirmed this evaluation. Although bond dissociation energy values of bonds in BPTU molecule are less than those in DPTU molecule, but the reaction rates of DPTU are greater than those of BPTU when reacting with HOO (selected as a representative free radical), so the IC50 values of DPTU were smaller than IC50 of BPTU. On the basis of kinetic calculations, hydrogen atom transfer (HAT) is supposed to be a preferred mechanism over single electron transfer (SET) when thiourea derivatives reacted with free radicals. The amount of products obtained according to HAT mechanism accounts for 99.99% compared with the product amount of HAT and SET mechanisms.