Synthesis, Characterization and Antioxidant Studies of Thiosemicarbazide Derived Schiff Bases

Ho, Sheng Zhou (2019) Synthesis, Characterization and Antioxidant Studies of Thiosemicarbazide Derived Schiff Bases. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Schiff bases are compounds that possessed imine functional group and many Schiff bases were reported to be chemically and biological important. This project was carried out to study and compare the antioxidant ability of thiosemicarbazide derived Schiff bases. In this project, three thiosemicarbazide derived Schiff bases have been synthesized by condensation reaction of trans-cinnamaldehyde and 4-methyl-3-thiosemicarbazide, 4-ethyl-3-thiosemicarbazide and 4-phenyl-3-thiosemicarbazide respectively in absolute ethanol. The synthesized Schiff bases were purified by recrystallization in absolute ethanol or ethyl acetate. Characterization of the synthesized Schiff bases was done with Differential Scanning Calorimetry (DSC), Fourier Transform Infrared-Attenuated Total Reflection spectrometer (FTIR-ATR), Ultraviolet-Visible (UV-Vis) spectrophotometer and 1H and 13C Nuclear Magnetic Resonance (NMR) spectrometer. The characterization results of synthesized Schiff bases were tally with the corresponding proposed structure. In vitro antioxidant activity of synthesized Schiff bases was evaluated against 1, 1-diphenyl 2-picrylhydrazyl (DPPH) free radical scavenging assay and Ferric Reducing Ability of Plasma (FRAP) assay. The result revealed that (E)-N-phenyl-2-((E)-3-phenylallylidene)hydrazine-1-carbothioamide (PTCA) exhibited best antioxidant activity among three synthesized Schiff bases in both antioxidant assays. The good antioxidant activity of PTCA might be contributed by its side phenyl ring. However, PTCA was not able to replace ascorbic acid as potency antioxidant as ascorbic acid showed lower IC50 in this study.