Synthesis, Characterization, and Biological Activities of Novel Vanadium(IV) and Cobalt(II) Complexes

Abstract

Herein, we report novel Co­(II) and V­(IV) complexes synthesized from an (E)-2-(((2-((2-hydroxyethyl)­amino)­quinolin-3-yl)­methylene)­amino)­ethan-1-ol ligand (L), cobalt­(II) chloride hexahydrate, and vanadyl­(IV) sulfate in methanolic solutions. The ligand and the complexes were characterized by 1H NMR spectroscopy,13C NMR spectroscopy, UV–visible spectroscopy, fluorescence spectroscopy, FT-IR spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDX), mass spectroscopy (MS), thermal analysis, and molar conductance. The FT-IR spectral data showed that the ligand adopted a tridentate fashion when binding with the metal ions via the nitrogen atoms of the imine (CN) and amine (N–H), and the oxygen atom of the hydroxyl group (O–H). The PXRD and SEM results indicated that the complexes are amorphous in nature. The density functional theory (DFT) calculated absorption and IR spectra agree very well with the corresponding experimental results. The antibacterial activities of the free ligand and its complexes were evaluated using a paper disk diffusion method. The complexes have better percent activitiy index than the free ligand. The cobalt complex exhibited a more recognizable antibacterial activity than the vanadium complex, specifically against Pseudomonas aeruginosa with a mean inhibition zone of 18.62 ± 0.19 mm, when compared with the positive control, ciprofloxacin, with a mean inhibition zone of 22.98 ± 0.08 mm at the same concentration. Furthermore, the antioxidant activities of the free ligand and its metal complexes were also determined in vitro using 2,2-diphenyl-1-picrylhydrazyl. The ligand exhibited less in vitro antioxidant activity than its transition metal complexes, in which the cobalt complex has a better antioxidant activity with half-inhibitory concentrations (IC50 of 16.01 μg/mL) than the ligand and the vanadium complex. Quantum molecular descriptors from the DFT calculations further support the experimental results. Molecular docking analysis also shed more light on the biological activities of the novel cobalt and vanadium complexes.

Novel Zinc(II) and Copper(II) Complexes of 2-((2-Hydroxyethyl)amino)quinoline-3-carbaldehyde for Antibacterial and Antioxidant Activities: A Combined Experimental, DFT, and Docking Studies

“…The metal complexes showed intense fluorescent intensities as compared with their precursor ligand ( Figure 3 ). 13 …”

“… 44 A stock solution of the sample (1000 μg/mL) was prepared freshly in methanol, solutions of different concentrations (1.56, 3.13, 6.25, 12.5, 25, 50, 100, and 200 μg/mL) were prepared from the stock solution, and 1 mL of 0.004% DPPH solution was added to the above test solutions according to the previous studies. 13 , 45 The mixture was shaken vigorously and incubated for 30 min, and then the absorbance was measured at 517 nm in triplicate and ascorbic acid was used as a positive control parallel to the test compounds. In the absence of the test sample, 1 mL of the DPPH solution in 1 mL of methanol was used as the negative control.…”

“… 51 This method has been used and gave results, which are in good agreement with the corresponding experimental results in our previous studies. 13 , 52 − 54 Methanol and the polarizable continuum model in its integral equation formalism (IEF-PCM) 55 were employed to mimic the experimental synthesis method and consider solvent effects. The same method and level of theory as that of the geometry optimizations was employed to calculate the frequencies and confirm that the optimized geometries are real minima.…”

“…The graphical analysis of the data was performed using GraphPad Prism version 5.00 (GraphPad Software, California). 13 , 58 Hence, the analysis of variance (ANOVA) test on behalf of correlation with significance ( p < 0.05) was evaluated for significant differences with groups ( Table S1 ).…”

“… 5 , 6 In relation to this, we recently investigated and reported the coordinating ability of quinoline derivative ligand complexed with Zn(II), Cu(II), Co(II), Ni(II), and V(IV) metal ions and evaluated their biological activities. 13 This work introduces new Zn(II) and Cu(II) metal complexes with new quinoline derivative ligand 2-((2-hydroxyethyl)amino)quinoline-3-carbaldehyde. In addition, we studied the binding stoichiometry, formation constants, antimicrobial activities, and antioxidant activities using spectroscopy, disk diffusion, and DPPH assay methods.…”