Synthesis, Characterisation, Antioxidant and Antimicrobial Activity Studies of Thiosemicarbazide Derived Schiff Base and Its Metal Complexes

Chong, Oscar Jun Jie (2025) Synthesis, Characterisation, Antioxidant and Antimicrobial Activity Studies of Thiosemicarbazide Derived Schiff Base and Its Metal Complexes. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

In this study, one novel thiosemicarbazide derived Schiff base, (E)-4-{3-[2-(methylcarbamothioyl)hydrazineylidene]butyl}phenyl acetate (MTACT) was synthesised via conventional condensation method, while its zinc (II) and copper (II) complexes, Zn(MTACT)2 and Cu(MTACT)2, were synthesised under reflux conditions. These synthesised compounds were characterised via melting point analysis, DSC, ATR-FTIR, UV-Vis, 1H/13C NMR, LC-ESI-MS, CHNS, and FAAS. Structural studies confirmed that MTACT exists in the thione (C=S) form in both solid and liquid states, as verified by single-crystal X-ray diffraction, whereas Zn(MTACT)2 and Cu(MTACT)2 adopt the deprotonated thiol (C–S–) tautomeric form in the solid state. The antioxidant activities of MTACT, Zn(MTACT)2 and Cu(MTACT)2 along with their raw materials, were tested via DPPH and FRAP assays. Both antioxidant assays showed a consistent activity trend: MT > MTACT > Cu(MTACT)2 > Zn(MTACT)2 > Cu(OAc)2H2O > Zn(OAc)22H2O > ACT. The reduced antioxidant activities of the metal complexes compared to the parent ligand are likely due to steric hindrance that limits free radical scavenging. The antimicrobial activities of the synthesised compounds were evaluated via disc diffusion and MD assays. Only Zn(MTACT)2 and Cu(MTACT)2 exhibited weak activity against Gram-positive bacteria (S. aureus), while none of the compounds showed inhibitory effects against the Gram-negative bacteria (E. coli). The enhanced antimicrobial activities of both metal complexes compared to their parent ligand may be attributed to their great lipophilicity, which facilitates microbial cell penetration. These findings demonstrate that metal complexation significantly enhances antimicrobial activity, but do not enhance antioxidant activity of thiosemicarbazide derived Schiff base. Keywords: Thiosemicarbazide; Schiff base; Metal complexes; Antioxidant; Antimicrobial.