Antioxidant, antimicrobial, DNA binding and cleavage studies of novel Co(II), Ni(II) and Cu(II) complexes of N, O donor Schiff bases: Synthesis and spectral characterization

Synthesis, Structural Characterization, and Computational Studies of Novel Co(II) and Zn(II) Fluoroquinoline Complexes for Antibacterial and Antioxidant Activities

Research into heterocyclic ligands has increased in popularity due to their versatile applications in the biomedical field. Quinoline derivatives with their transition metal complexes are popular scaffolding molecules in the ongoing pursuit of newer and more effective bioactive molecules. Subsequently, this work reports on the synthesis and possible biological application of new Zn(II) and Co(II) complexes with a bidentate quinoline derivative ligand (H2 L), [(H2 L):(E)-2-(((6-fluoro-2-((2-hydroxyethyl)amino)quinolin-3-yl)methylene)amino)ethanol]. The ligand and its metal complexes were structurally characterized by spectroscopic methods (1H NMR, 13C NMR, Fourier transform infrared (FTIR), UV-vis, fluorescence, and mass spectroscopy), as well as by thermogravimetric and elemental analysis methods. The spectroscopic findings were further supported by density functional theory (DFT) and time-dependent (TD)-DFT calculations. The biological application was examined by investigating the inhibitory action of the complexes against bacterial strains using diffusion and agar dilution methods, and their profiles against two Gram-positive and Gram-negative bacterial strains were supported by molecular docking analysis. To rationalize the in vitro activity and establish the possible mechanism of action, the interactions and binding affinity of the ligand and complexes were investigated against three different bacterial enzymes (Escherichia coli DNA gyrase (PDB ID 6f86), E. coli dihydrofolate reductase B (PDB ID: 7r6g), and Staphylococcus aureus tyrosyl-tRNA synthetase (PDB ID: 1JIJ)) using AutoDock with the standard protocol. The MIC value of 0.20 μg/mL for zinc complex against E. coli and associated binding affinities -7.2 and -9.9 kcal/mol with DNA gyrase (PDB ID 6f86) and dihydrofolate reductase B (PDB ID: 7r6g), as well as the MIC value of 2.4 μg/mL for cobalt(II) complex against Staphylococcus aureus and the associated binding affinity of -10.5 kcal/mol with tyrosyl-tRNA synthetase (PDB ID: 1JIJ), revealed that the complexes' inhibitory actions were strong and comparable with those of the standard drug in the experiments. In addition, the ability of the new quinoline-based complexes to scavenge 1,1-diphenyl-picrylhydrazyl radicals was investigated; the findings suggested that the complexes exhibit potent antioxidant activities, which may be of therapeutic significance.

Design, Synthesis, Structural Investigation and Photo Induced Biological Investigations of Co(II), Ni(II) and Cu(II) Complexes Derived from N,O Donor Schiff Bases

A series of chelated metal complexes, [Co(LI)2] (1), [Ni(LI)2] (2), [Cu(LI)2] (3) [Co(LII)2] (4), [Ni(LII)2] (5) and [Cu(LII)2] (6) were designed and synthesized from newly synthesized Schiff bases, LI = 2-((E)-(5-(4-fluorophenyl)isoxazol-3-ylimino)methyl)-5-methylphenol and LII = 2-((E)-(5-(4-fluorophenyl)isoxazol-3-ylimino)methyl)-4-chlorophenol. The synthesized compounds were characterized by elemental analysis, nuclear magnetic resonance spectroscopy (NMR), electronic spectroscopy (UV-Vis), infrared spectroscopy (FT-IR), magnetic susceptibility (µeff), electron spin resonance spectroscopy (ESR), Thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and powder X-ray diffraction analysis (P-XRD). The spectral investigations have been clearly suggested 1:2 (metal: ligand) stoichiometric complexes with square planar geometrical arrangement around the metal ion. The thermal gravimmetric analysis (TGA) of these complexes indicates greater thermal stability and various steps involved in thermal decomposition of metal complexes. The binding ability between these metal complexes and calf thymus DNA (CT-DNA) was investigated by UV-Vis, fluorescence spectroscopy and viscometric experiments, which disclosed that, the complexes interacted to CT-DNA via an intercalation binding mode. The cleavage property of metal complexes against pBR322 DNA has been explored by gel electrophoresis technique mediated by UV-illumination and H2O2, showed momentous cleavage activity. Antioxidant activity of all complexes was determined by DPPH free radical scavenging experiment and showed prominent antioxidant activity. Further, the antibacterial and antifungal activities of all compounds were screened against bacterial and fungal strains via in-vitro disc diffusion method. These studies revealed that the complexes showed comparatively more antimicrobial activity than free ligands against tested microbial strains.

Synthesis and DFT calculations of metal(II) oxime complexes bearing cysteine as coligand and investigation of their biological evolutions in vitro and in silico

New complexes with the formula of [ML(Cys)(H2O)2] were obtained as a result of the reaction between the oxime ligand [HL: 4-(4-bromophenylaminoisonitrosoacetyl)biphenyl], cysteine (Cys), and the metal(II) salts (Mn, Ni, Co, Zn, Cu). The newly synthesized compounds were characterized using conventional techniques such as molar conductance, magnetic measurements, elemental analysis, infrared spectroscopy, and thermal analysis (TGA/DTA). Based on the conductivity measurements in DMF, it was determined that the complexes were non-electrolytes. The TGA/DTA analysis was performed to examine the thermal stability and degradation behavior of all samples, and results demonstrated that metal oxides or sulfides formed as a result of the decompositions. In conjunction with other data obtained, the elemental analysis confirmed the octahedral coordination of the complexes with deprotonated oxime (O, O-donor) and amino acid (N, S-donor) ligands and two coordinated waters. The compounds' optimized geometries, molecular electrostatic potential diagrams, and frontier molecular orbitals were computed at the DFT/B3LYP level using the 6-311 G(d,p) and LANL2DZ basis sets. The antibacterial and DNA cleavage activities of all synthesized compounds were also screened, and molecular docking simulations were performed. According to the results of molecular docking studies conducted with three different proteins, the best interaction was found to be between HL-1HNJ with a binding energy of -9.5 kcal/mol. The stability of the HL-1HNJ complex was also verified by a molecular dynamics simulation performed for 50 ns.Communicated by Ramaswamy H. Sarma.

Exploring the antioxidant, antimicrobial, cytotoxic and biothermodynamic properties of novel morpholine derivative bioactive Mn(ii), Co(ii) and Ni(ii) complexes - combined experimental and theoretical measurements towards DNA/BSA/SARS-CoV-2 3CLPro

A novel class of bioactive complexes (1-3) [MII(L)2(bpy)], where, L = 2-(4-morpholinobenzylideneamino)phenol, bpy = 2,2'-bipyridine, MII = Mn (1), Co (2) or Ni (3), were assigned to octahedral geometry based on analytical and spectral measurements. Gel electrophoresis showed that complex (2) demonstrated significant DNA cleavage activity compared to the other complexes under the action of oxidation agent (H2O2). The DNA binding constant properties measured by various techniques were in the following sequence: (2) > (3) > (1) > (HL), which suggests that the complexes might intercalate DNA, a possibility that is also supported by their biothermodynamic characteristics. The binding constant results for BSA from electronic absorption and fluorometric titrations demonstrate that complex (2) exhibits the highest binding effectiveness among them all, which means that all the compounds could interact with BSA through a static approach, additionally supported by FRET measurements. DFT and docking calculations were employed to realize the electronic structure, reactivity, and interaction capability of all substances with DNA, BSA, and the SARS-CoV-2 main protease. These binding energies fell within the ranges -7.7 to -8.5, -8.2 to -10.1 and -6.7 to -9.3 kcal mol-1, respectively. The higher reactivity of the complexes than the ligand is supported by FMO theory. The in vitro antibacterial, cytotoxicity, and radical scavenging characteristics revealed that complexes (2-3) have better biological efficacy than the others. The cytotoxicity and binding properties also show good correlation with the partition coefficient (log P), which is encouraging because all of the experimental findings are closely correlated with the theoretical measurements.

Synthesis, characterization, and biological activities of zinc(II), copper(II) and nickel(II) complexes of an aminoquinoline derivative

Interest is increasingly focused on the use of transition metal complexes as biochemical, medical, analytical, pharmaceutical, agronomic, anticancer, and antibacterial agents. In this study, three complexes of [Zn(H2L)Cl] (1), [Cu(H2L)(H2O)(NO3)] (2) and [Ni(H2L)(NO3)].2H2O (3) were synthesized from a 2-chloroquinoline-3-carbaldehyde derived ligand [H3L = ((E)-2-(((2-((2-hydroxyethyl)amino)quinolin-3-yl)methylene)amino)ethanol. The compounds were characterized using physicochemical and spectroscopic methods. The results demonstrate that the free ligand behaves as a tridentate ligand with one oxygen and two nitrogen (ONN) donor atoms in 1:1 metal:ligand ratio. The formation constants of the complexes were found to be (KZn(II) = 2.3 × 106, KCu(II) = 2.9 × 106, and KNi(II) = 3.8 × 105). The thermodynamic parameters indicated that the reactions were spontaneous with exothermic nature of metal-ligand interaction energies. Based on the analyses of the experimental (EDX, FTIR, PXRD, MS and TGA) and DFT results, a distorted tetrahedral, a distorted square pyramidal and square planar geometry for Zn(II), Cu(II) and Ni(II) complexes, respectively, were proposed. The B3LYP calculated IR frequencies and TD-B3LYP calculated absorption spectra were found to be in good agreement with the corresponding experimental results. The powder XRD data confirmed that the Zn(II), Cu(II) and Ni(II) complexes have polycrystalline nature with average crystallite sizes of 27.86, 33.54, 37.40 Å, respectively. In vitro antibacterial activity analyses of the complexes were studied with disk diffusion method, in which the complexes showed better activity than the precursor ligand. Particularly the Cu(II) complex showed higher percent activity index (62, 90%), than both Zn(II) (54, 82%) and Ni(II) (41, 68%) complexes against both E. coli and P. aeruginosa, respectively. Using the DPPH assay, the complexes were further assessed for their antioxidant capacities. All metal complexes showed improved antioxidant activity than the free ligand. Zn(II) and Cu(II) complexes, which had IC50 values of 10.46 and 8.62 μg/ml, respectively, showed the best antioxidant activity. The calculated results of Lipinski’s rule of five also showed that the target complexes have drug-like molecular nature and similarly, the results of binding mode of action of these compounds against E. coli DNA gyrase B and P. aeruginosa LasR.DNA were found to be in good agreement with the in vitro biological activities.

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

In the present work, two novel complexes of zinc(II) and copper(II) were synthesized from the ligand 2-((2-hydroxyethyl)amino)quinoline-3-carbaldehyde (H ₂ L) in a 1:2 metal-to-ligand ratio in methanol. The complexes were characterized by UV-visible spectroscopy, fluorescence spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), mass spectrometry (MS), nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA) experimental techniques and density functional theory (DFT) calculations. The spectral data revealed that the mono-deprotonated (HL) ligand acted as a bidentate ligand, which bound to both Zn(II) and Cu(II) ions via the nitrogen atom of the amine (N-H) and the hydroxyl (O-H) groups through the deprotonated oxygen atom. Formation constants and thermal analysis indicated that both metal complexes are stable up to 100 °C with thermodynamically favored chemical reactions. The Cu(II) complex showed antibacterial activities with the zones of inhibition of 20.90 ± 2.00 mm against Pseudomonas aeruginosa, 19.69 ± 0.71 mm against Staphylococcus aureus, and 18.58 ± 1.04 mm against Streptococcus pyogenes. These results are relatively higher compared with the Zn(II) complex at the same concentration. The minimum inhibitory concentration (MIC) results for the complexes also showed similar trends against the three bacteria. On the other hand, radical scavenging activities of both Cu(II) and Zn(II) complexes showed half-maximal inhibitory concentrations (IC₅₀) of 4.72 and 8.2 μg/mL, respectively, while ascorbic acid (a positive control) has a value of 4.28 μg/mL. The Cu(II) complex exhibited better communication with the positive control, indicating its potential use for biological activities. The calculated and in silico molecular docking results also strongly support the experimental results.

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

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.