Antibacterial, antioxidant and cytotoxicity evaluation of selected schiff base ligands and their corresponding metal complexes
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Date
2025
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University of Namibia
Abstract
Schiff bases are compounds that possess an azomethine group and are considered as
aldehyde and ketone derivatives. Schiff bases have diverse pharmacological
properties and constitute an important class of compounds for new drug development
hence researchers are investigating these compounds for different biological
activities. The present study was designed to synthesize Schiff base ligands and their
metal complexes which were then screened for antibacterial and antioxidant activity
as well as cytotoxicity against a cervical cancer cell line. Schiff base ligands were
synthesized by means of the Schiff’s base reaction, and for each ligand, metal
complexes of copper II (Cu2+) and nickel II (Ni2+) were synthesized. The structural
confirmation of the synthesized compounds was done by Proton Nuclear Magnetic
Resonance (1H NMR) and Fourier Transform Infrared (FTIR) spectroscopies. The
antibacterial activity of the ligands and metal complexes was assayed by means of
the agar disc diffusion method while the antioxidant activity was determined using
the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and reducing power assays. Cytotoxicity
studies were conducted against Henrietta Lacks (HeLa) cells using the 3-(4,5-
dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Both ligands
and metal complexes displayed antibacterial activity against strains of
Staphylococcus aureus, Streptococcus mutans, Neisseria gonorrhoea, and
Escherichia coli with minimum inhibitory concentration (MIC) values ranging from
2.5 – 10 mg/mL. All tested compounds demonstrated a concentration-dependent
antioxidant activity, with half maximal inhibitory concentration (IC50) values in the
range of 1.33 – 85.81 µg/mL. Selected ligands and metal complexes exhibited
cytotoxic activity against HeLa cells, having IC50 values in the range of 4.12 – 16.80
µg/mL. Copper metal complexes exhibited the best antibacterial activity with
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recorded MIC of 2.5 mg/mL against most tested bacteria species. On the other hand,
nickel metal complexes had the best antioxidant activity with IC50 values of 1.33 –
33.92 µg/mL. Most ligands and metal complexes exhibited moderate cytotoxicity
against HeLa cells. However, L6 was the most toxic to HeLa cells as indicated by a
lower IC50 (4.12 ± 0.6 µg/mL), compared to other compounds tested for cytotoxicity
in the present study. There are no literature reports on the antibacterial, antioxidant
and cytotoxic activities of the compounds analysed in this study. The results
generated from this study showed that the biologically active ligands and metal
complexes could be used as compounds of interest in the drug discovery process
Description
A Dissertation submitted in fulfilment of the requirement for the Degree of Doctor of Philosophy in Science in Biochemistry
Keywords
Antioxidant, Antibacteriel, Cytotoxicity, Metal complexes, Namibia, University of Namibia