Preparation, structure elucidation, and antioxidant activity of new bis(thiosemicarbazone) derivatives

Abstract

Schiff-base-bearing new bis(thiosemicarbazone) derivatives were prepared from terephthalaldehyde and various thiosemicarbazides. FT-IR, ¹H NMR, ¹³C NMR, and UV-Vis spectroscopic methods and elemental analysis were used to elucidate the identification of the synthesized molecules. The in vitro antioxidant activity of the synthesized compounds was analysed with the 1,1-diphenyl-2-picryl hydrazyl free-radical-trapping process. The synthesized compounds exhibited lower antioxidant activity than the standard ascorbic acid. IC₅₀ values of the synthesized molecules measured from 3.81 ± 0.01 to 29.05 ± 0.11 μM. Among the synthesized compounds, compound 3 had the best antioxidant activity. Moreover, this study explained the structure-activity relationship of the synthesized molecules with different substituents in radical trapping reactions.

Keywords: DPPH; Schiff bases; Thiosemicarbazides; spectroscopic methods; structure–activity relationship.

Scheme 1

Synthetic route for bis(thiosemicarbazones) based on Schiff base (1–10).

Figure 1

FT-IR spectrum of compound 4.

Figure 2

¹H NMR spectrum of compound 4 .

Figure 3

¹³C NMR spectrum of compound 4.

Figure 4

UV–Vis spectrum of compound 5 in DMSO.

Figure 5

Percentage of inhibition calculated by the DPPH method for ascorbic acid and compounds 1–10.