Synthesis, characterization and antibacterial Properties of copper (II) complexes of schiff bases derived from benzophenone derivatives and selected anilines

Abstract

In every region of the world, antibiotic resistance is increasing to dangerously high levels. The emergence and global dissemination of new bacterial resistance threaten human beings' capacity to cure widespread infectious diseases. As antibiotics lose their effectiveness, many infections, including blood poisoning, pneumonia, and tuberculosis, become difficult to cure and occasionally incurable. Therefore, there is a pressing need to develop new antibacterial agents to address this resistance. Thus, this study entailed synthesizing, characterizing, and determining the antibacterial activities of the Schiff base and its copper (II) complexes. The Schiff base ligands were synthesized by mixing 2-hydroxy-4-methoxybenzophenone with selected anilines in a 1:1 ratio, followed by refluxing for 3-4 hours. The precipitate obtained was filtered and dried at room temperature. The Cu (II) complexes were prepared in a 2:1 ratio by treating a hot solution of Schiff base ligands dissolved ethanol with an aqueous Cu (II) chloride under 4 hours of refluxing. The synthesized compounds melted at a constant temperature, confirming that they were pure. The Schiff base ligands and their Cu (II) complexes were characterized using various analytical techniques such as Fourier Transform-Infrared (FT-IR), Ultra Violet-Visible (UV-VIS) and Proton Nuclear Magnetic Resonance (1H-NMR) spectroscopy and molar conductance measurements. The FT-IR data of the Schiff base ligands displayed the absence of NH2 and C=O, confirming the formation of azomethine group (-HC=N-) at region 1610-1631.78cm1 which shifted to lower wavelengths upon complexation with Cu (II) ions. The peak due to OH appeared at 3420-3450 cm-1 but later disappeared due to formation Cu (II) complex. The appearance of two new peaks 475.46-480.28 and 523.68581.55cm-1 in the Cu (II) complex spectra attributed to Cu-O and Cu-N, respectively. UV-vis spectra of the free ligands appeared at 40322.58-41580cm-1 due to the transition of non-bonding electrons of azomethine nitrogen. Molar conductance measurements of Cu (II) complexes range from 13.34-22.208(Scm2mol-1), while that of free ligands range from 4.86-12.58 (Scm2mol-1), confirming they were nonionic. 1H NMR analysis of free ligands in deuterated DMSO-d6 revealed the presence of the presence of OH group at δ 11.81-12.65 ppm, which disappear upon complexing with Cu (II) ions. The antibacterial sensitivity levels of the Schiff base ligands and their Cu (II) complexes were determined using the disk diffusion method. The synthesized compounds tested for antibacterial bioassay against two gram-negative bacteria, Pseudomonas aeruginosa and Escherichia coli and one gram-positive bacterium, Staphylococcus aureus, at 4 different concentrations. All synthesized compounds show antibacterial activities against all bacteria strains. The zones of inhibition ranged from 6.00- 21.00 mm. However, no test compound showed higher inhibition zones than gentamycin and amoxiclav (positive controls). Data was analyzed using Two-Way ANOVA. The results showed a significant difference (p ≤ 0.05) between the means, indicating that methyl, nitro and carboxyl groups and coordination of the ligands to Cu (II) affected antibacterial activity. Cu (II) complexes displayed higher antibacterial activity than their free ligands. It was concluded that the substituted ligands with methyl, carboxyl and nitro groups and Cu (II) complexes have promising antibacterial activity. The results suggest potential applications of Schiff base ligands obtained from benzophenone derivatives and their Cu (II) complexes as antibacterial agents.