Structural analysis, antimicrobial and cytotoxic studies on new metal(II) complexes containing N2O2 donor Schiff base ligand

Design, synthesis, DFT calculations, molecular docking and antimicrobial activities of novel cobalt, chromium metal complexes of heterocyclic moiety-based 1,3,4-oxadiazole derivatives

A Schiff base, 5-(4-methylphenyl)-4-[(pyridin-2-ylmethylidene)amino]-4H-1,2,4-oxadiazole as a bidentate ligand has been synthesized by the reaction between the 4-amino-5-(4-methylphenyl)-4H-1,3,4-oxadiazole and aromatic aldehyde. The Schiff base reacted with CoCl₃·6H₂O and CrCl₃·6H₂O in ethanol to yield 1,3,4-oxadiazole complexes. The structures of synthesized ligand and their complexes have been established on the basis of their IR, Mass and ¹H-NMR spectra. Electronic and geometric structures of both cobalt and chromium complexes were investigated by density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) calculations. DFT-based reactivity calculations estimated the studied system as strong electrophile and/or strong nucleophile in polar organic reactions. Moreover, most reactive sites were predicted theoretically based on the delocalized and localized indexes. The nature of Ligand-Metal chemical bonding is discussed in terms of the natural bond orbital (NBO) and QTAIM analysis. Accordingly, the metal ions such as cobalt and chromium are bidentate coordinated with the Schiff base by nitrogen atoms of imine function and pyridine, to form stable complexes. Furthermore, the chromium ions have an affinity superior to the cobalt ions towards Schiff base ligand. In addition, the results of the antibacterial activity in-vitro show that the metal complexation confers an increase in the antibacterial activity of the complexed ligand compared to the free ligand against both Gram-positive and Gram-negative bacteria with broad spectrum activity. In silico molecular docking studies of the ligands and their complexes were applied to describe the probable binding modes into the active site of Escherichia coli (E. coli) FabH and Salmonella typhimurium LT2 neuraminidase (STNA) receptors. The increase in biological activity could be attributed to the high stability of the complexes and strong affinities to bacterial enzyme receptors.Communicated by Ramaswamy H. Sarma.

Water-soluble nickel (II) Schiff base complexes: Synthesis, structural characterization, DNA binding affinity, DNA cleavage, cytotoxicity, and computational studies

Two water-soluble nickel (II) Schiff base complexes were prepared and their interaction with fish sperm DNA (FS-DNA) was investigated by various methods including UV-vis spectroscopy, fluorescence spectroscopy, cyclic voltammetry, and viscometric measurements. Complex 1: [N,N'-bis{5-[(triphenyl phosphonium chloride)-methyl] salicylidine}-3,4-diaminobenzophenone]nickel(II) perchloride dihydrate: [Ni(5-CH₂PPh₃-3,4-salophen)] (ClO₄)₂.2 H₂O was synthesized as a new complex and characterized by elemental analysis, IR, ¹H NMR, thermal gravimetric analysis (TGA) and UV-vis spectroscopy. Complex 2: sodium [(N,N'-bis(5-sulfosalicyliden)-3, 4-diaminobenzophenone)aqua] nickel(II) hydrate: Na₂[Ni (5-SO₃-3,4-salbenz)(H₂O)]. H₂O was already synthesized by our research team, but in this study, its function as a DNA-binding compound was tested, and compared with the results of complex 1-DNA binding. The calculation of different constants using absorption and emission data, all confirmed the stronger binding ability of complex 1 than complex 2 with DNA. Different thermodynamic parameters showed the interactions between DNA and complexes were the type of hydrophobic interaction for complex 1 and electrostatic interaction for complex 2. Also, the negative values of free energy changes proved a spontaneous DNA binding process. Based on cell toxicity assay against two different cell lines including Jurkat and MCF-7, the effect of complex 1 was comparable to cisplatin, and the toxicity mechanism was further justified by bright field microscopy, flow cytometry, and cleavage of DNA in the presence of H₂O₂. Besides, the docking calculations suggested intercalation after measuring the lowest-energy between the complexes and DNA. For both complexes, all analytical, spectroscopic, and molecular modeling methods supported partial intercalation as the main binding mode between the complexes and DNA.

DNA-Binding and Cytotoxicity of Copper(I) Complexes Containing Functionalized Dipyridylphenazine Ligands

A set of copper(I) coordination compounds with general formula [CuBr(PPh₃)(dppz-R)] (dppz-R = dipyrido[3,2-a:2’,3’-c]phenazine (Cu-1), 11-nitrodipyrido[3,2-a:2’,3’-c]phenazine (Cu-2), 11-cyanodipyrido[3,2-a:2’,3’-c]phenazine (Cu-3), dipyrido[3,2-a:2’,3’-c]phenazine-11-phenone (Cu-4), 11,12-dimethyldipyrido[3,2-a:2’,3’-c]phenazine (Cu-5)) have been prepared and characterized by elemental analysis, ¹H-NMR and ³¹P-NMR spectroscopies as well as mass spectrometry. The structure of Cu-1 was confirmed by X-ray crystallography. The effect of incorporating different functional groups on the dppz ligand on the binding into CT-DNA was evaluated by absorption spectroscopy, fluorescence quenching of EtBr-DNA adducts, and viscosity measurements. The functional groups affected the binding modes and hence the strength of binding affinities, as suggested by the changes in the relative viscosity. The differences in the quenching constants (K_sv) obtained from the fluorescence quenching assay highlight the importance of the functional groups in altering the binding sites on the DNA. The molecular docking data support the DNA-binding studies, with the sites and mode of interactions against B-DNA changing with the different functional groups. Evaluation of the anticancer activities of the five copper compounds against two different cancer cell lines (M-14 and MCF-7) indicated the importance of the functional groups on the dppz ligand on the anticancer activities. Among the five copper complexes, the cyano-containing complex (Cu-3) has the best anticancer activities.

Enhancement of Schiff base biological efficacy by metal coordination and introduction of metallic compounds as anticovid candidates: a simple overview

In the prevailing apocalyptic times of coronavirus disease (COVID-19), the whole scientific community is busy in designing anticovid drug or vaccine. Under such a fascination, Schiff bases or azomethine compounds are continuously interrogated for antimicrobial properties. These compounds represent interesting molecular scaffolds of huge medicinal and industrial relevance. In order to update the current literature support of such facts this article introduces the synthetic chemistry, mechanism of formation of a Schiff base, followed by biological efficacy and finally a suitable discussion on the mechanism of respective bioactivity. In most of the studies revealing the biological evaluation of azomethine functionalized frameworks, fascinated results have been recorded in case of azomethine-metal complexes as compared with the free ligands. Also, the CH=N or C=N form of organic ligands have indicated marvellous results. Therefore, in connection with the biological relevance and microbicidal implications of such metallic compounds, this works reviews the current update of microorganism fighting efficacy of azomethine metal complexes along with the introduction of some metallodrugs as excellent candidates having COVID-19 defending potentiality.

Computational investigation of molecular structures, spectroscopic properties and antitumor-antibacterial activities of some Schiff bases

Molecular structures, spectroscopic properties (IR, ¹H NMR and ¹³C NMR, UV-VIS), molecular electrostatic potential maps and some molecular properties (ionization energy, electron affinity, energy gap, hardness, electronegativity, electrophilicity index, static dipole moment and average linear polarizability) of three Schiff bases which are 2-((ethylamino)methyl)-6-methoxyphenol (HL1), 2-((ethylamino) methyl)-6-methylphenol (HL2) and 2-((ethylamino)methyl)-6-chlorophenol (HL3) were computed at B3LYP/6-31G(d) level in aqueous phase. The effects of methoxy, methyl and chloro substituents on Schiff bases were examined and it was found that the electron donating property of methyl and chlorine substituents was higher than the methoxy substituent. In order to investigate the antitumor activities of Schiff bases were docked against the breast cancer (MCF7) cell line. Molecular docking results were compared with antitumor standard 5-fluorouracil. Antitumor activity of HL2 and HL3 molecule was found to be higher than HL1 against MCF-7 cell line. In addition, in order to predict the antibacterial activities of Schiff bases were docked against the Mycobacterium tuberculosis (H37Rv) cell line. Docking results were compared with the antibacterial reference N-(salicylidene)-2-hydroxyaniline. Antibacterial activity of HL2 and HL3 molecules was found to be higher than HL1. It is estimated that the binding of the electron donating group to the ortho position of the hydroxyl group in studied Schiff bases increases both antitumor and antibacterial activity.

Synthesis, characterization, antiproliferative of pyrimidine based ligand and its Ni(II) and Pd(II) complexes and effectiveness of electroporation

In the study, a new Schiff base (ligand) was obtained using 4-aminopyrimidine-2(1H)-one, the starting material, and 2,3,4-trimethoxy benzaldehyde. Ni(II) and Pd(II) complexes were obtained from the reaction of the ligand and NiCl₂·6H₂O, PdCl₂(CH₃CN)₂ (1:1 ratio). These compounds were characterized using the elemental and mass analysis, ¹H, ¹³C-NMR, FT-IR, UV-Vis, magnetic susceptibility, thermal analysis, and the X-ray diffraction analyses. The antiproliferative activities of the synthesized ligand, Ni(II) and Pd(II) complexes were identified on the HepG2 (human liver cancer cells) cell line and their biocompatibility was tested on the L-929 (fibroblast cells) cell line by the MTT analysis method. Furthermore, the effects of electroporation (EP) on the cytotoxic activities of synthesized compounds were investigated in HepG2 cancer cells. According to the MTT findings of the study, the ligand did not exhibit an antiproliferative activity while its Ni(II) and Pd(II) complexes exhibited an antiproliferative activity. Moreover, it was observed that the antiproliferative activity of the Pd(II) complex was stronger than that of the Ni(II) complex. The combined application of EP + compounds is much more effective than the usage of the compounds alone in the treatment of HepG2 cancer cells. The EP increased the cytotoxicity of the Ni(II) and Pd(II) complexes by 1.66, and 2.54 times, respectively. It was concluded that Ni(II) and Pd(II) complexes may contribute as potential anti-cancer agents for the treatment of hepatocellular carcinoma and yield promising results in the case of being used in ECT.Communicated by Ramaswamy H. Sarma.

A novel coumarin-derived acylhydrazone Schiff base gelator for synthesis of organogels and identification of Fe3

A novel coumarin-derived acylhydrazone Schiff base fluorescent organogel (G₁) was designed and synthesized. Gelator G₁ can form stable organogels in isopropanol, tert-amyl alcohol, n-butanol and phenylamine. The organogel could be converted to solution by heating and the solution could be restored to gel state by cooling. The self-assemble mechanism of G1 was investigated by XRD, FT-IR and SEM techniques. The results indicated the intermolecular hydrogen bonding, Van der Waals interaction and π-π stacking are the forces for the self-assembly of the gelator to form the organogel. The optical properties of the compound were studied by UV-visible spectroscopy and fluorescence spectra. Further study presented that gelator G1 could selectively and sensitively response to Fe³⁺ only among tested cations. Beside the above functions, the organic gel factor G1 could also response to irradiation, heating and shaking, thus endowing the organogel with multi stimulus responsive properties.

Efficient and Environmentally Friendly Adsorbent Based on β-Ketoenol-Pyrazole-Thiophene for Heavy-Metal Ion Removal from Aquatic Medium: A Combined Experimental and Theoretical Study

A new sustainable and environmentally friendly adsorbent based on a β-ketoenol-pyrazole-thiophene receptor grafted onto a silica surface was developed and applied to the removal of heavy-metal ions (Pb(II), Cu(II), Zn(II), and Cd(II)) from aquatic medium. The new material SiNPz-Th was well characterized and confirms the success of covalent binding of the receptor on the silica surface. The effect of environmental parameters on adsorption including pH, contact time, temperature, and the initial concentration were investigated. The maximum adsorption capacities of SiNPz-Th for Pb(II), Cu(II), Zn(II), and Cd(II) ions were 102.20, 76.42, 68.95, and 32.68 mg/g, respectively, at 30 min and pH = 6. The adsorption isotherms, kinetics, and thermodynamic process were investigated and showed efficiency and selectivity toward Pb(II) and good regeneration performance. Density functional theory, noncovalent-interaction, and quantum theory of atoms in molecules calculations were used to study and to gain a deeper understanding of both the adsorption mechanism and selectivity of metal ions onto the adsorbent. Accordingly, metal ions such as Pb(II), Cu(II), and Zn(II) were bidentate coordinated with the adsorbent by nitrogen and oxygen atoms of the Schiff base C=N and hydroxyl group -OH, respectively, to form stable complexes. Whereas Cd(II) was coordinated in a monodentate fashion with oxygen atom of the hydroxyl group. Furthermore, the affinity of SiNPz-Th toward the metal ions was decreased in the order of Pb(II) > Cu(II) > Zn(II) > Cd(II), in good agreement with the experimental results. All these results highlight that SiNPz-Th has good potential to be an advanced adsorbent for the removal of lead ions from real water.

Crystal structure of (E)-1-(2-nitrophenyl)-N-(o-tolyl)methanimine, C14H12N2O2

C14H12N2O2, monoclinic, P21, a = 8.3844(1) Å, b = 20.0465(3) Å, c = 14.0511(2) Å, β = 94.786(1)°, V = 2353.44(6) Å3, Z = 4, R gt(F) = 0.0356, wR ref(F 2) = 0.1022, T = 150(2) K.