Synthesis, characterization, DFT calculation and antibacterial activities of new cupper complexes containing novel thiourea derivatives

On the basis of the pharmacological studies of the compounds containing carbonyl and thiocarbonyl groups such as urea, thiourea and their related analogues, it is proposed that the thiourea derivatives and their transition metal complexes represent a wide diversity of biological functions including antibacterial, antifungal, anti-diabetic, antitubercular, anti-human immunodeficiency virus (anti-HIV), anti-Hepatitis C virus (anti-HCV), antitumor, antithyroid, anthelmintic, rodenticidal, insecticidal, herbicidal,and plant-growth regulator properties [1]. In this study, three new thiourea ligands derived from the condensation of aroyl- and aryl-isothiocyanate derivatives with 2,6-diaminopyridine, named 1,1 -(pyridine-2,6- diyl)bis(3-(benzoyl)thiourea), 1,1 -(pyridine-2,6-diyl)bis(3-(2-chlorobenzoyl)thiourea) and 1,1 -(pyridine-2,6-diyl)bis(3-(4-chlorophenyl)thiourea) and their cupper complexes were synthesized and characterized by elemental analysis, FTIR and 1H NMR and UV-visible spectroscopies. Proposed structures for free thiourea ligands and their cupper complexes were corroborated by applying geometry optimization and conformational analysis. These compounds were studied in vitro in terms of antibacterial properties against Staphylococcus aureus and Enterococcus faecalis and Escherichia coli and Pseudomonas aeruginosa as 2 standard gram-positive and 2 standard gram-negative bacterial strains, respectively, through minimum Inhibitory Concentration by using the broth macrodilution procedure and inhibition zone via the disk diffusion method. The infrared spectra of these samples exhibit all the expected frequency regions of the (N–H), (C=S), (C=O) and (C–N). Electronic excitation study of these samples in DMSO solution displays several absorption bands in the UV and visible regions. All compounds inhibited the growth of bacteria with MIC values ranging between 64 and 1024 μg/ml. On precise examination of the theoretical results, it can be found that antibacterial activities have some relationship with theLUMO energies and the difference between LUMO and HOMO energies.We find that the thickness of inhibition zones for abovenamed standard bacterial strains is linearwith these features in some samples. The experiments showed that cupper complexes had the superior antibacterial activities than novel thiourea derivatives against all Gram-positive and Gram-negative bacterial strains.