Synthesis, structure, polyphenol oxidase mimicking and bactericidal activity of a zinc-schiff base complex

Synthesis, Spectral Characterization, Antimicrobial Activity, DFT Calculations, Molecular Docking and ADME Studies of Novel Schiff Base Co(II), Ni(II), Cu(II) and Zn(II) Complexes Derived from 4-nitro-ortho-phenylenediamine

A condensation reaction was carried out between 4-nitro-ortho-phenylenediamine and 5-bromosalicyaldehyde to synthesize a novel Schiff base ligand 2,2'-[(1E,1'E)-(4-nitro-1,2-phenylene) bis (azaneylylidene) bis (methaneylylidene)] bis (4-bromophenol) [NB] in the current investigation. This was followed by the synthesis of metallic complexes comprising the Co(II), Ni(II), Cu(II) and Zn(II) transition metal ions. A hexadentate environment encircling metal complexes was corroborated by the results of varied spectroscopic methods that were employed to unravel the structure of the ligand and metal complexes. The Tauc's plot and Urbach energy were utilized for quantifying the optical energy band gap to provide insight into optical characteristics. The Coats-Redfern method of thermal analysis was implemented to do the kinetic and thermodynamic calculations. Furthermore, DFT studies were performed to predict geometrical structures and the stability of the compounds. Thorough investigation to evaluate their biological efficacies, docking studies was executed against COVID-19 main protease (PDB-7VAH), Dengue virus NS2B/NS3 protease (PDB-2FOM) and Mycobacterium Tuberculosis (PDB-5AF3). Apart from this, in silico ADMET studies were also accomplished for elucidation of drug likeness characteristics and the results attained disclose the significant proficiency of synthesized compounds. Besides this, antimicrobial studies were assessed with different microbial strains and result validates cobalt and zinc complexes as most potent against the selected bacterial and fungal strains.

A benzimidazole scaffold as a promising inhibitor against SARS-CoV-2

The manuscript reports the green-chemical synthesis of a new diindole-substituted benzimidazole compound, B1 through a straightforward route in coupling between indolyl-3-carboxaldehyde and o-phenylenediamine in water medium under the aerobic condition at 75 ºC. The single crystal X-ray structural analysis of B1 suggests that the disubstituted benzimidazole compound crystallizes in a monoclinic system and the indole groups exist in a perpendicular fashion with respect to benzimidazole moiety. The SARS-CoV-2 screening activity has been studied against 1 × 10e4 VeroE6 cells in a dose-dependent manner following Hoechst 33342 and nucleocapsid staining activity with respect to remdesivir. The compound exhibits 92.4% cell viability for 30 h and 35.1% inhibition against VeroE6 cells at non-cytotoxic concentration. Molecular docking studies predict high binding propensities of B1 with the main protease (M^pro) and non-structural (nsp2 and nsp7-nsp8) proteins of SARS-CoV-2 through a number of non-covalent interactions. Molecular dynamics (MD) simulation analysis for 100 ns confirms the formation of stable conformations of B1-docked proteins with significant changes of binding energy, attributing the potential inhibition properties of the synthetic benzimidazole scaffold against SARS-CoV-2. Communicated by Ramaswamy H. Sarma.

Schiff base compounds as artificial metalloenzymes

Much research has been done on traditional homogeneous metal catalysts and enzymatic catalysts, but recently a new class of hybrid catalysts called synthetic (artificial) metalloenzymes has been considered by researchers. Metalloenzymes as hybrid catalysts (host-guest systems) have been shown that combine the properties of a homogeneous and also enzymatic catalyst. The hybrid catalyst will have added value such as enantioselectivity or chemo-selectivity. This review focuses on Schiff base complexes that either act as homogeneous artificial enzymes or contribute to the structure of a host in the preparation of hybrid metalloenzymes. Because this approach can virtually be applied to any bio- or synthetic host or guest coordination complex, the details of hybrid catalysts seem important for advance in catalysis.

Polyphenol-Enriched Composite Bone Regeneration Materials: A Systematic Review of In Vitro Studies

One of the possible alternatives for creating materials for the regeneration of bone tissue supporting comprehensive reconstruction is the incorporation of active substances whose controlled release will improve this process. This systematic review aimed to identify and synthesize in vitro studies that assess the suitability of polyphenolics as additives to polymer-ceramic composite bone regeneration materials. Data on experimental studies in terms of the difference in mechanical, wettability, cytocompatibility, antioxidant and anti-inflammatory properties of materials were synthesized. The obtained numerical data were compiled and analyzed in search of percentage changes of these parameters. The results of the systematic review were based on data from forty-six studies presented in nineteen articles. The addition of polyphenolic compounds to composite materials for bone regeneration improved the cytocompatibility and increased the activity of early markers of osteoblast differentiation, indicating a high osteoinductive potential of the materials. Polyphenolic compounds incorporated into the materials presumably give them high antioxidant properties and reduce the production of reactive oxygen species in macrophage cells, implying anti-inflammatory activity. The evidence was limited by the number of missing data and the heterogeneity of the data.

Synthesis and crystal structures of new mixed-ligand Schiff base complexes containing N-donor heterocyclic co-ligands: molecular docking and pharmacophore modeling studies on the main proteases of SARS-CoV-2 virus (COVID-19 disease)

Three new mixed-ligand copper(II) complexes (1–3) with NN'O type unsymmetrical tridentate Schiff base ligands (SB) and N-donor heterocyclic co-ligands, with general formula [Cu(SB)(L)]ClO₄, were synthesized and characterized using single crystal x-ray diffraction (SCXRD), FT-IR and UV–Vis spectroscopy and elemental analyses. The SB ligand is the half-unit form of the condensation of 1,3-propanediamine with 5-methoxysalicylaldehyde and the co-ligands (L) are pyridine (py in (1)), 2,2′-bipyridine (bpy in (2)) and 1,10-phenanthroline (phen in (3)). Crystal structures of (2) and (3) were obtained by SCXRD. Molecular docking and pharmacophore studies were performed to study the interactions between the synthesized complexes and SARS-CoV-2 virus main proteases (PDB IDs: 6LU7, 6WQF and 6W9C). Results revealed that complex (3) with phen co-ligand showed better docking scores with the three receptors, i.e. 6LU7 (−8.05 kcal.mol⁻¹), 6W9C (−7.70 kcal.mol⁻¹) and 6WQF (−7.75 kcal.mol⁻¹). The order of the binding best energies for (3) was also as follows: 6LU7 > 6WQF > 6W9C. All of the studied complexes showed considerable performance, comparable to the standard drug, Favipiravir.

De novo synthesis of hybrid d-f block metal complex salts for electronic charge transport applications

The advent of d-d type complex salts for designing smart functional materials with versatile utility inspired us to develop a novel type of M(II)-Ce(IV) complex salts [M(II) = Cu and Zn ions]. In this study, we present for the first time a holistic approach to design and prepare metal complex salts of the novel hybrid d-f block type, [Cu(bpy)₂]₂[Ce(NO₃)₆]₂ (1), [Cu(phen)₂(NO₃)]₂[Ce(NO₃)₆](HNO₃) (2), [Zn(bpy)₂(NO₃)][ClO₄] (3), and [Zn(phen)₂(NO₃)]₂ [Ce(NO₃)₆] (4); [bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline]. The intrinsic structural and morphological properties of the compounds have been revealed by employing a suite of analytical and spectroscopic methods. X-ray structural analysis reveals that the copper(II) centres in the cationic complex units of 1 and 2 adopt a highly distorted tetrahedral and a rare bicapped square pyramidal coordination geometry, respectively. The zinc(II) ions in both 3 and 4 adopt the rare bicapped square pyramidal geometry while the cerium(IV) ions in 1, 2 and 4 exist in a dodecahedral geometry. Investigation of supramolecular interactions reveals that intermolecular O⋯H and O⋯π short contacts bind the complex units in 1, while predominant π⋯π interactions, along with O⋯H and O⋯π short contacts, produce the binding force among the complex units in 2. We further employed the complex salts (1-4) to construct Schottky devices to reveal the role of these new complex salts in the charge-transport phenomenon. The carrier mobilities (μ) for salts 1-4 were determined to be 1.76 × 10^-6, 9.02 × 10^-6, 1.86 × 10^-8, and 4.31 × 10^-8 m² V^-1 s^-1, with respective transit times (τ) of 439, 85, 4.17 × 10³, and 1.79 × 10³ ns, which suggest that complex salt 2 is the best candidate with the highest transport properties among all the complex salts. A crystal engineering perspective sheds light on the charge-transport properties of the complex salts, emphasizing the attribution of the best performance of 2 to its predominant π⋯π interactions. The synthesis of this new type of complex salts, their physicochemical properties and their charge-transport applications envisage great promise for the development of novel crystalline materials with smart functionalities.

Schiff Base Driven Denticity-Fluctuated Structural Assortment of Zinc-pseudohalide Complexes: Synthesis, Structures and Electrical Transport Properties

We report peculiar characteristics of a polydentate Schiff base towards zinc(II) ion in the presence of pseudohalides (thiocyanate and azide) and the charge transport properties of the zinc complexes mediated...

A hemilabile 2-(2′-pyridyl)-imidazole based nickel(ii) complex: proton-coupled-electron-transfer, bactericidal and cytotoxicity studies

This study deals with the synthesis, structural characterization, proto-coupled-electron-transfer, bactericidal and cytotoxicity study of a hemilabile and water-soluble 2-(2′-pyridyl)-imidazole nickel(ii) complex.

A hydrated 2,3-diaminophenazinium chloride as a promising building block against SARS-CoV-2

Phenazine scaffolds are the versatile secondary metabolites of bacterial origin. It functions in the biological control of plant pathogens and contributes to the producing strains ecological fitness and pathogenicity. In the light of the excellent therapeutic properties of phenazine, we have synthesized a hydrated 2,3-diaminophenazinium chloride (DAPH+Cl-·3H2O) through direct catalytic oxidation of o-phenylenediamine with an iron(III) complex, [Fe(1,10-phenanthroline)2Cl2]NO3 in ethanol under aerobic condition. The crystal structure, molecular complexity and supramolecular aspects of DAPH+Cl- were confirmed and elucidated with different spectroscopic methods and single crystal X-ray structural analysis. Crystal engineering study on DAPH+Cl- exhibits a fascinating formation of (H2O)2…Cl-…(H2O) cluster and energy framework analysis of defines the role of chloride ions in the stabilization of DAPH+Cl-. The bactericidal efficiency of the compound has been testified against few clinical bacteria like Streptococcus pneumoniae, Escherichia coli, K. pneumoniae using the disc diffusion method and the results of high inhibition zone suggest its excellent antibacterial properties. The phenazinium chloride exhibits a significant percentage of cell viability and a considerable inhibition property against SARS-CoV-2 at non-cytotoxic concentration compared to remdesivir. Molecular docking studies estimate a good binding propensity of DAPH+Cl- with non-structural proteins (nsp2 and nsp7-nsp-8) and the main protease (Mpro) of SARS-CoV-2. The molecular dynamics simulation studies attribute the conformationally stable structures of the DAPH+Cl- bound Mpro and nsp2, nsp7-nsp8 complexes as evident from the considerable binding energy values, - 19.2 ± 0.3, - 25.7 ± 0.1, and - 24.5 ± 0.7 kcal/mol, respectively.

Bioactive Tryptophan-Based Copper Complex with Auxiliary β-Carboline Spectacle Potential on Human Breast Cancer Cells: In Vitro and In Vivo Studies

Biocompatible tryptophan-derived copper (1) and zinc (2) complexes with norharmane (β-carboline) were designed, synthesized, characterized, and evaluated for the potential anticancer activity in vitro and in vivo. The in vitro cytotoxicity of both complexes 1 and 2 were assessed against two cancerous cells: (human breast cancer) MCF7 and (liver hepatocellular cancer) HepG2 cells with a non-tumorigenic: (human embryonic kidney) HEK293 cells. The results exhibited a potentially decent selectivity of 1 against MCF7 cells with an IC50 value of 7.8 ± 0.4 μM compared to 2 (less active, IC50 ~ 20 μM). Furthermore, we analyzed the level of glutathione, lipid peroxidation, and visualized ROS generation to get an insight into the mechanistic pathway and witnessed oxidative stress. These in vitro results were ascertained by in vivo experiments, which also supported the free radical-mediated oxidative stress. The comet assay confirmed the oxidative stress that leads to DNA damage. The histopathology of the liver also ascertained the low toxicity of 1.