Synthesis, characterization and antibacterial activity Of selected schiff base ligands and their copper Complexes

Abstract

Resistant strains of bacteria have emerged because of improper use of antibiotics and insufficient infection management, posing a serious danger to both public health and the global economy. Therefore, it has become essential to produce a new generation of antimicrobials to slow the spread of antibiotic resistance. This is by advancement of antimicrobial drugs that can specifically interact with a target site of a particular pathogen. The work described in this paper entails the synthesis, characterization and antibacterial evaluation of schiff base ligands and their Cu (II) complexes. The ligands, Ligand 1 ((E)-N,N-dimethyl1-4-((p-tolyimino)methyl)aniline) and Ligand 2 ((E)4(((2,4-dinitrophenyl)imino)methyl)-n-n-dimethylaniline), were obtained by microwave assisted condensation and then refluxed for 3 hours, the solid was filtered and rinsed with ethanol and left to dry. The copper complexes were prepared by treating a hot (40°C) solution of the ligands dissolved in ethanol with an aqueous solution of Cu (II) chloride followed by refluxing for 3 hours. Ultraviolet Visible spectroscopy and Fourier Transform Infrared Spectroscopy characterized each of the synthesized compounds. The percentage yield was at 78% for ligand 1, 62% for ligand 2, 76% for complex 1 and 81% for complex 2. The UV-Visible spectra showed two major absorption bands for the ligands, which shifted to higher and lower wavelengths for the complexes. The FTIR spectra show that the azomethine (-C=N-) stretch shifts from 1640.0 cm ¹ in the ligands to 1635.64 cm ¹ in complex 1 and 1614.42 cm ¹ in complex 2. Similarly, the carbonyl (-C-O-) stretch shifts from 1238.00 cm ¹ (Ligand 1) and 1160.00 cm¹ (Ligand 2) to lower values in complex 1 (1027.00 cm¹) and complex 2 (1141.00 cm¹), confirming metal-ligand interaction. The antibacterial sensitivity levels of the synthesized Schiff bases and the Cu (II) complexes was evaluated using disk diffusion method. The bacterial strains employed included; GramPositive staphylococcus aureus and Gram-negative Escherichia coli. The filter paper discs were deepen into concentration ranging from 10ug/ml-40ug/ml for every compound synthesized and then laid onto the surface of the discs. The average inhibition zone for the ligands was at 7.0 mm (ligand 1) and 6 mm (ligand 2) for gram negative bacteria and 10.5 mm (ligand 1) and 10.75 (ligand 2) for Gram positive bacteria. For the complexes 6.0 mm (complex 1) and 6.75 mm (complex 2) for gram negative bacteria and 9.5mm (Complex 1) and 8.75 mm (complex 2) for gram positive bacteria relative to standard gentamycin which showed activity at 24 mm for gram negative and 26 mm for gram positive bacteria. These results were relative to the literature work done, however the zones were slightly lower. From these results, it is concluded that the ligands and complexes were successfully synthesized and all these compounds showed promising activity against bacteria. To explore further potential of these compounds, further studies on other antimicrobial properties as antiviral, antifungal among others should be performed to evaluate similar performance.