Abstract
Despite the common use of salens and hydroxyquinolines as therapeutic and bioactive agents, their metal complexes are still under development. Here, we report the synthesis of novel mixed-ligand metal complexes (MSQ) comprising salen (S), derived from (2,2′-{1,2-ethanediylbis[nitrilo(E) methylylidene]}diphenol, and 8-hydroxyquinoline (Q) with Co(II), Ni(II), Cd(II), Al(III), and La(III). The structures and properties of these MSQ metal complexes were investigated using molar conductivity, melting point, FTIR, 1H NMR, 13C NMR, UV–VIS, mass spectra, and thermal analysis. Quantum calculation, analytical, and experimental measurements seem to suggest the proposed structure of the compounds and its uncommon monobasic tridentate binding mode of salen via phenolic oxygen, azomethine group, and the NH group. The general molecular formula of MSQ metal complexes is [M(S)(Q)(H2O)] for M (II) = Co, Ni, and Cd or [M(S)(Q)(Cl)] and [M(S)(Q)(H2O)]Cl for M(III) = La and Al, respectively. Importantly, all prepared metal complexes were evaluated for their antimicrobial and anticancer activities. The metal complexes exhibited high cytotoxic potency against human breast cancer (MDA-MB231) and liver cancer (Hep-G2) cell lines. Among all MSQ metal complexes, CoSQ and LaSQ produced IC50 values (1.49 and 1.95 µM, respectively) that were comparable to that of cisplatin (1.55 µM) against Hep-G2 cells, whereas CdSQ and LaSQ had best potency against MDA-MB231 with IC50 values of 1.95 and 1.43 µM, respectively. Furthermore, the metal complexes exhibited significant antimicrobial activities against a wide spectrum of both Gram-positive and -negative bacterial and fungal strains. The antibacterial and antifungal efficacies for the MSQ metal complexes, the free S and Q ligands, and the standard drugs gentamycin and ketoconazole decreased in the order AlSQ > LaSQ > CdSQ > gentamycin > NiSQ > CoSQ > Q > S for antibacterial activity, and for antifungal activity followed the trend of LaSQ > AlSQ > CdSQ > ketoconazole > NiSQ > CoSQ > Q > S. Molecular docking studies were performed to investigate the binding of the synthesized compounds with breast cancer oxidoreductase (PDB ID: 3HB5). According to the data obtained, the most probable coordination geometry is octahedral for all the metal complexes. The molecular and electronic structures of the metal complexes were optimized theoretically, and their quantum chemical parameters were calculated. PXRD results for the Cd(II) and La(III) metal complexes indicated that they were crystalline in nature.
Highlights
Metal complexes constitute an important class of materials and are encountered daily
Motivated by the uncommon tridentate salen binding in its mixed-ligand metal complexes with imidazole MSI, together with our growing interest in the properties/applications of Schiff base metal complexes, we report in this contribution the synthesis, photophysical properties, and DFT calculations of new mixed-ligand of salen/8-hydroxyquinoline metal complexes (MSQ; M = Co(II), Ni(II), and Cd(II), or Al(III) and La(III) ions)
The protein was prepared for the docking as follows: (i) The ligand molecule was removed from the enzyme active site. (ii) Hydrogen atoms were added to the proteins with MOE and minimized, keeping all the heavy atoms fixed until RMS gradient of 0.01 kcal/mol and RMS distance of 0.1 Å were reached. (iii) Partial charges were computed using MMFF94x force field. (iv)The structures of salen and its metal complexes were created in PDB file format using the Gaussian09 software package. (v) The structures were subjected to energy minimization using MMFF94x force field, and the partial charges were computed using the same force field. (vi) Docking calculations were performed using Alpha triangle placement method, and poses were ranked by London dG scoring method
Summary
Metal complexes constitute an important class of materials and are encountered daily. 8-Hydroxyquinoline (typically abbreviated to Q in its metal complexes) and its derivatives are found in plants and have been prepared synthetically Owing to their chelating ability towards many metal cations, hydroxyquinoline derivatives have found many applications. They are used as preservatives in the textile industry and as fungicides in the agricultural, paper, and wood industries [25]. Analytical and theoretical (DFT) structural characterizations revealed a mono basic tridentate coordination mode of the salen ligand and bidentate for 8-hydroxyquinoline to afford octahedral geometries of the general formula [M(S)(Q)(X)], X = H2O or Cl. Importantly, the antimicrobial activities of the prepared MSQ metal complexes were evaluated and compared with those of their salen/imidazole MSI analogues. The cytotoxicity of the MSQ metal complexes against the liver carcinoma (Hep-G2) and the breast cancer (MDA-MB231) carcinoma cell lines were investigated
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