An experimental and computational study of antioxidant activity of N-phenylthiourea and N-phenylselenourea analogues

The antioxidant performance of N-phenylthiourea has been experimentally studied via the half maximal inhibitory concentration value (IC₅₀) in combination with quantum calculations. In the experimental part, DPPH•(1,1-diphenyl-2-picrylhydrazyl) radical scavenging ability of N-phenylthiourea (IC₅₀) was measured to be 4.82.10^-4 M. Based on three antioxidant mechanisms being hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SETPT) and sequential proton loss electron transfer (SPLET), the essential thermoparameters of N-phenylthiourea derivatives were carried out at ROB3LYP/6-311++G(2df,2p)//B3LYP/6-311G(d,p) in both gas phase and ethanol in order to evaluate their antioxidant capacity. For the sake of comparison, N-phenylselenourea derivatives were also taken into account. The computational results indicated that the antioxidant of N-phenylselenourea is better than that of N-phenulthiourea. Besides, potential energy surfaces of N-phenylselenourea derivatives and •HOOradical were investigated. All the reactions were thermodynamically favored. The derivatives containing the electron donating group at the para position of N-phenylselenourea considerably enhanced their antioxidant capacity. As a result, para-N(CH₃)₂-C₆H₄-NH-CSe-NH₂ was the best potential antioxidant in the studied compounds. (author)