Synthesis, characterization and DFT investigation of new metal complexes of Ni(II), Mn(II) and VO(IV) containing N,O-donor Schiff base ligand

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.

Metal complexes containing vitamin B6-based scaffold as potential DNA/BSA-binding agents inducing apoptosis in hepatocarcinoma (HepG2) cells

A ligand (HL) was synthesized from the pyridoxal hydrochloride (vitamin B6 form) and 1-(2-Aminoethyl)piperidine in one single step. The metal complexes [Zn(L)(Bpy)]NO3 (1), [Cu(L)(Bpy)]NO3 (2), and [Co(L)(Bpy)]NO3 (3) were prepared by tethering HL and 2,2'-bipyridine. The synthesized HL and metal complexes 1-3 were thoroughly characterized using spectroscopic techniques such as 1H NMR, 13C NMR, FTIR, EI-MS, molar conductance, and magnetic moment, in addition to CHN elemental analysis. The geometry of complexes was square pyramidal around the metal ions {Zn(II), Cu(II), and Co(II)}. The interaction of ligand and metal complexes with DNA and BSA macromolecules was accomplished by UV-Vis absorption and fluorescence spectroscopy in vitro. The hyperchromism in band at 303-325 with no shift supports the groove binding with some partial intercalation in grooves. Similarly, in BSA-binding studies, complex 2 shows greater binding potential in the hydrophobic core probably near the Trp-212 in the subdomain IIA. Furthermore, complex 2 shows excellent cytotoxicity on HepG2 cancer cells with IC50 = 25.0 ± 0.45 µM. The detailed analysis by cell-cycle studies shows cell arrest at the G2/M phase. The type of cell death was authenticated by an annexin V-FTIC dual staining experiment that reveals maximum death by apoptosis together with non-specific necrosis.

Synthesis and Spectroscopic Characterization of Schiff Base Metal Complexes, Biological Activity, and Molecular Docking Studies

New cobalt(II), copper(II), and zinc(II) Schiff metal complexes were synthesized by the condensation reaction of 4-nitrobenzene-1,2-diamine with 3-4-(diethylamino)-2-hydroxybenzaldehyde. Fourier transform infrared, nuclear magnetic resonance, ultraviolet-visible, electron paramagnetic resonance, and high-resolution electrospray ionization mass spectrometry and powder X-ray diffraction were used to characterize the synthesized H2L and its metal complexes. Conductance measurements, magnetic moment estimation, and metal estimation have all been determined and discussed. The electrochemical properties of the synthesized compounds have been determined and discussed using cyclic voltammetry. The molecular structures of H2L and its metal complexes have been optimized using the B3LYP functional and the 6-31G (d,p) basis set, and their parameters have been discussed. The quantum chemical properties of these synthesized compounds have been predicted through charge distribution and molecular orbital analysis. The biological properties of the synthesized compounds' antioxidant, antifungal, and antibacterial activity have been studied and discussed. Furthermore, H2L and its complexes have been docked with HER2-associated target proteins in breast cancer.

Chemical, Pharmacological, and Theoretical Aspects of Some Transition Metal(II) Complexes Derived from Pyrrole Azine Schiff Base

Some new transition metal complexes were prepared by reacting metal(II) salts with Schiff base azines, which were prepared via condensation of 5-(diethylamino) salicylaldehyde and hydrazine with pyrrole-2-carbaldehyde. Their structures were confirmed based on CHN, UV-visible, FT-IR, and EPR measurements. The complexes were also assessed for their antibacterial, antioxidant, and anticancer properties. Some of these chemicals were said to be extraordinarily effective in this respect. The antibacterial activities of the complexes in vitro demonstrated their potential, although the [Cu(L)(bpy] complex was suggested to exhibit moderate activity against pathogens compared to all other in this series. The cytotoxic activity of the prepared analogues showed better cell viability compared with standard cisplatin. Moreover, there is a good agreement between the experimental and theoretical findings from docking and theoretical investigations done using DFT at the B3LYP level.

Triazole based Schiff bases and their Oxovanadium(IV) complexes: Synthesis, characterization, antibacterial assay, and computational assessments

The synthesis and characterization of two new Schiff base ligands containing 1,2,4-triazole moieties and their oxovanadium(IV) complexes have been reported. The ligands and their complexes were studied by ultraviolet-visible (UV-Vis), Fourier transform infrared (FTIR), proton nuclear magnetic resonance (¹H NMR), electron paramagnetic resonance (EPR), X-ray diffraction (XRD), conductivity measurement, cyclic voltammetry (CV), and elemental analyses. The molar conductance of oxovanadium(IV) complexes were found to be relatively low, depicting their non-electrolytic nature. The XRD patterns reveal the size of particles to be 47.53 nm and 26.28 nm for the two complexes in the monoclinic crystal system. The molecular structures, geometrical parameters, chemical reactivity, stability, and frontier molecular orbital pictures were determined by density functional theory (DFT) calculations. The theoretical vibrational frequencies and EPR g-factors (1.98) were found to correlate well with the experimental values. A distorted square pyramidal geometry with C₂ symmetry of the complexes has been proposed from experimental and theoretical results in a synergistic manner. The antimicrobial sensitivity of the ligands and their metal complexes assayed in vitro against four bacterial pathogens viz. Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Salmonella Typhi showed that the oxovanadium(IV) complexes are slightly stronger antibacterial agents than their corresponding Schiff base precursors. The binding affinities obtained from the molecular docking calculations with the receptor proteins of bacterial strains (2EUG, 3UWZ, 4GVF, and 4JVD) showed that the Schiff bases and their oxovanadium(IV) complexes have considerable capacity inferring activeness for effective inhibition. The molecular dynamics simulation of a protein-ligand (4JVD-HL₂) complex with the best binding affinity of -12.8 kcal/mol for 100 ns showed acceptable stability of the docked pose and binding free energy of -15.17 ± 2.29 kcal/mol from molecular mechanics-generalized Born surface area (MM-GBSA) calculations indicated spontaneity of the reaction. The outcome of the research shows the complementary role of computational methods in material characterization and provides an interesting avenue to pursue for exploring new triazole based Schiff's bases and its vanadium compounds for better properties.

Synthesis and X-ray structure analysis of cytotoxic heptacoordinated Salan hafnium(IV) complexes stabilized with 2,6-dipicolinic acid

Four novel Salan Hf^(IV) complexes stabilized by 2,6-dipicolinic acid (Dipic) were synthesized and characterized by ¹H, ¹³C NMR and X-ray diffraction spectroscopy. These Hf^(IV)bis-chelates could be obtained in good to excellent yields (88%-91%) and demonstrated rather good stability in aqueous media and on silica gel. [L₂Hf^(IV)Dipic^4-H,Cl] containing steric bulk L₂ were stable in about 10% H₂O (H₂O/THF (v/v)), however, [L₁Hf^(IV)Dipic^4-H,Cl] with non-steric L₁ could slowly dissociate and release nontoxic L₁. [L_1-2Hf^(IV)Dipic^4-Cl] showed excellent anti-tumoral activity in the range of cisplatin (Hela S3: IC₅₀ = 3.5 ± 0.4 μM, Hep G2: IC₅₀ = 11.2 ± 2.1 μM). In addition, the cellular uptake and apoptosis investigation of [L₁Hf^(IV)Dipic^4-Cl] suggested a fast cellular uptake process against Hela S3 cells with an almost exclusive induced apoptosis cell death path.

An unexpected single crystal structure of nickel(II) complex: Spectral, DFT, NLO, magnetic and molecular docking studies

This work explores the study of a synthesized nickel complex as a possible inhibitor against the main protease (Mpro) of the recent emerging coronavirus disease (COVID-19). Overall, the template reaction of 3-acetyl-2-hydroxy-6-methyl-4H-pyran-4-one with nickel(II) chloride hexahydrate in N,N-dimethylformamide (DMF) medium leads to the formation of neutral nickel complex. This resulting complex is formulated as [Ni(DHA)₂(DMF)₂] on the basis of FT-IR, UV-Vis., single-crystal X-ray diffraction analysis, magnetic susceptibility and CV measurements as well as DFT quantum chemical calculations. Its single crystal suggests was found to be surrounded by the both pairs of molecules of DHA and DMF through six oxygen atoms with octahedral coordination sphere. The obtained magnetic susceptibilities are positive and agree with its paramagnetic state. In addition to the experimental investigations, optimized geometry, spectroscopic and electronic properties were also performed using DFT calculation with B3LYP/6-31G(d,p) level of theory. The nonlinear optical (NLO) properties of this complex are again examined. Some suitable quantum descriptors (E_HOMO, E_LUMO, Energy gap, Global hardness), Milliken atomic charge, Electrophilic potion and Molecular Electrostatic Potential) have been elegantly described. Molecular docking results demonstrated that the docked nickel complex displayed remarkable binding energy with Mpro. Besides, important molecular properties and ADME pharmacokinetic profiles of possible Mpro inhibitors were assessed by in silico prediction.

Electrochromic behavior of fac-tricarbonyl rhenium complexes

Tricarbonyl rhenium complex shows good electrochromic performance with a colored stage of green, rapid response and good switching stability.