Synthesis, characterisation and biological studies of transition metal complexes (Cu, Zn, Ni) derived from amino acids

The arising of cancer and bacterial infections had become one of the concerns of the public due to high mortality rate. Hence, there is a need of searching for new drugs with higher activity. Metal complexes derived from amino acids have attracted much attention because of biological importance. In view of this, new amino acid-derived Schiff base complexes formed from various amino acids [L-phenylalanine (Phe), L-histidine (His), L-valine (Val), and L-methionine (Met)], dicarbonyl compounds [acetyl acetone (AA), glyoxal (G), 2,5-hexanedione (HD) and 5,5-dimethyl-1,3-cyclohexanedione(MHD)] and metal acetate salts [Cu(II), Ni(II) and Zn(II)] were synthesised. A total of 47 metal complexes were synthesised using template method. These complexes were characterised by various physico-chemical and spectroscopic methods. The FT-IR spectra indicated the presence of the C=N band around the region of 1600 cm-1 which proved the successful formation of the Schiff base. The Schiff bases were tetra-coordinated to the metal ion in 1:1 mol ratio via the azomethine nitrogen atom and carboxylate oxygen atom in the manner of N2O2. Based on the data obtained, the geometry of the complexes were either distorted tetrahedral or distorted square planar for the four-coordinated complexes, square pyramidal for NiGVal and ZnAAVal and distorted octahedral for NiHDPhe, NiMHDHis, NiHDHis, NiGVal, ZnGVal and ZnGMet. The complexes were evaluated against two bladder cancer cell lines (invasive human bladder carcinoma cell line, EJ-28; minimum-invasive human bladder carcinoma cell line, RT-112), and various bacterial strains (B. cereus, S. aureus, Methicillin-resistant S. aureus, E. coli, K. pneumonia, S. typhimurium, and S. sonnei) for cytotoxic and antibacterial activity. MTT assay was used to determine the cytotoxic activity of the complexes. From the data obtained, CuAAPhe and CuGPhe were found to be active against RT-112 cells at 13.70 μM and 14.71 μM respectively. The anti-migratory properties of the inactive complexes were studied against EJ-28 cells. CuGPhe, CuMHDVal, ZnGPhe, ZnAAHis, and NiAAVal were found to be potential anti-migration agents for bladder cancer cells. Disc diffusion method and determination of minimum inhibitory concentration (MIC) were used in the antibacterial studies of the complexes. The data showed that the complexes were more active against Gram-positive bacteria than Gram-negative bacteria. The MIC data obtained for CuAAHis, ZnGPhe, CuMHDHis, ZnGHis, ZnGMet and ZnHDMet against S. aureus was 8 mg/mL. The electrochemical behavior of the Cu(II) complexes were determined via cyclic voltammetry. Cu(II) complexes derived from L-phenylalanine, L-histidine and L-valine were found to be potential mediators in lactate oxidase (LOx) biosensors.

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