Synthesis, In vitro Biological Studies of novel Homoleptic Ni(II) and Zn(II) Complexes of Thiosemicarbazide Derivative ligand

Abstract

Thiosemicarbazide derivatives are currently becoming an important class of S, N –donor ligands to form stable metal complexes showing some biological applications. In this study, thiosemicarbazide-based derivative (4-(4-Chlorophenyl)-1-(4-nitrophenyl) thiosemicarbazide (L) and its homoleptic Ni(II) and Zn(II) complexes were synthesized by modified standard procedures. The structures of the synthesized compounds were characterized by several techniques: Uv-vis, Fourier-transform infrared (FT-IR), proton nuclear magnetic resonance ( 1 H NMR), 13 C-NMR spectroscopy, and TG-analysis. To explore the capability of thiosemicarbazide and its metal complexes for growth inhibition of bacteria and as antioxidant potential, evaluation were performed against two Gram-positive bacteria ( Bacillus subtilis ATCC6633 and Staphylococcus aureus ATCC25923 ) and Gram-negative bacteria ( Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 ) using disc diffusion and DPPH method respectively. For the ligand (L ) , the antimicrobial tests revealed a higher antibacterial activity against gram-positive B. subtilis ( 4.24 ± 0.67 ) whereas the gram-negative E. coli bacteria show resistance. The metal complexes [Ni(L) 2 (H 2 O) 2 ] and [Zn(L) 2 ] showed good activity against S. aureus , with a mean inhibition zone of 12.86 ± 0.46 and 13.82± 0.46 mm diameter at 500 μg/mL, respectively compared to the standard drug Ciprofloxacin having inhibition zone of 11.0 ± 0.67mm diameter at 500 μg/mL. Both complexes also showed good antiradical potential (48.55% and 56.75% at 100µg/ml). The results indicate that the complexes showed higher antibacterial and antioxidant potential than the free ligand. Thus, this study indicates an insight towards thiosemicarbazide derivative as ligand through metal coordination could enhance bioactivities. Keywords: Thiosemicarbazide-derivative, Homoleptic-complex, Antibacterial, Antioxidant DOI: 10.7176/CMR/14-2-02 Publication date: May 31 st 2022