Synthesis of metal complexes involving Schiff base ligand with methylenedioxy moiety: spectral, thermal, XRD and antimicrobial studies

Manganese(II) and Zinc(II) metal complexes of novel bidentate formamide-based Schiff base ligand: synthesis, structural characterization, antioxidant, antibacterial, and in-silico molecular docking study

A new bidentate Schiff base ligand (C16H16Cl2N4), condensation product of ethylene diamine and 4-chloro N-phenyl formamide, and its metal complexes [M(C16H16Cl2N4)2(OAc)2] (where M = Mn(II) and Zn(II)) were synthesized and characterized using various analytical and spectral techniques, including high-resolution mass spectrometry (HRMS), elemental analysis, ultraviolet-visible (UV-vis), Fourier-transform infrared (FTIR) spectroscopy, AAS, molar conductance, 1H NMR, and powder XRD. All the compounds were non-electrolytes and nanocrystalline. The synthesized compounds were assessed for antioxidant potential by DPPH radical scavenging and FRAP assay, with BHT serving as the positive control. Inhibitory concentration at 50% inhibition (IC50) values were calculated and used for comparative analysis. Furthermore, the prepared compounds were screened for antibacterial activity against two Gram-negative bacteria (Staphylococcus aureus and Bacillus subtilis) and two Gram-positive bacteria (Escherichia coli and Salmonella typhi) using disk-diffusion methods, with amikacin employed as the standard reference. The comparison of inhibition zones revealed that the complexes showed better antibacterial activity than the ligand. To gain insights into the molecular interactions underlying the antibacterial activity, the ligand and complexes were analyzed for their binding affinity with S. aureus tyrosyl-tRNA synthetase (PDB ID: 1JIL) and S. typhi cell membrane protein OmpF complex (PDB ID: 4KR4). These analyses revealed robust interactions, validating the observed antibacterial effects against the tested bacterial strains.

Antifungal Activity, Structure-Activity Relationship and Molecular Docking Studies of 1,2,4-Triazole Schiff Base Derivatives

Fourteen novel Schiff base compounds (AS-1∼AS-14) containing 5-amino-1H-1,2,4-triazole-3-carboxylic acid and substituted benzaldehyde were successfully synthesized, and their structures were verified by melting point, elemental analysis (EA) and spectroscopic techniques (Fourier Transform Infra-Red (FT-IR) and Nuclear Magnetic Resonance (NMR)). In vitro hyphal measurements were used to investigate the antifungal activities of the synthesised compounds against Wheat gibberellic, Maize rough dwarf and Glomerella cingulate. The preliminary studies indicated that all compounds had good inhibitory effect on Wheat gibberellic and Maize rough dwarf, among which the compounds of AS-1 (7.44 mg/L, 7.27 mg/L), AS-4 (6.80 mg/L, 9.57 mg/L) and AS-14 (5.33 mg/L, 6.53 mg/L) showed better antifungal activity than that of the standard drug fluconazole (7.66 mg/L, 6.72 mg/L); while inhibitory effect against Glomerella cingulate was poor, only AS-14 (5.67 mg/L) was superior to that of fluconazole (6.27 mg/L). The research of structure-activity relationship exhibited that the introduction of halogen elements on the benzene ring and electron withdrawing groups at the 2,4,5 positions on the benzene ring was beneficial to the improvement of the activity against Wheat gibberellic, while the large steric hindrance was not conducive to the improvement of the activity. Additionally, except for AS-1, AS-3 and AS-10, the other compounds had one or several ratio systems to achieve synergistic effect after recombination with pyrimethamine, among which AS-7 had significant synergistic effect and was expected to be a combinated agent with application prospects. Finally, the molecular docking results of isocitrate lyase with Wheat gibberellic displayed that the presence of hydrogen bonds enabled stable binding of compounds to receptor proteins, and the residues of ARG A: 252, ASN A: 432, CYS A: 215, SER A: 436 and SER A: 434 were the key residues for their binding. Comparing the docking binding energy and biological activity results, it was revealed that the lower the docking binding energy was, the stronger the inhibitory ability of the Wheat gibberellic, when the same position on the benzene ring was substituted.

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.

Atricephenols A and B, two phenolic compounds from Indigofera atriceps Hook.f. (Fabaceae)

The phytochemical investigation of a previously unstudied species of the genus Indigofera, I. atriceps Hook.f. was undertaken and two new phenolic compounds, atricephenols A (1) and B (2) were isolated, along with nine known secondary metabolites viz., (-)-melilotocarpan D (3), genistein (4), melilotocarpan A (5), maackiain (6), p-hydroxybenzaldehyde (7), bornesitol (8), β-sitosterol (9), sitosterol-3-O-β-D-glucopyranoside (10) and stigmasterol-3-O-β-D-glucopyranoside (11). Their structures were elucidated by extensive NMR spectroscopic analyses and HRESIMS, and by comparing their data with those reported in the literature. Compounds 1, 4, 7-11 were tested for their antibacterial efficacies and for their potential to inhibit the enzyme urease. Compounds 7 and 9 showed significant antibacterial activity against Salmonella typhi (ZOIs of 13 and 15 mm, respectively), while the best urease inhibition was measured for compound 9 with an IC₅₀ value of 18.6 µM, which is higher than that of the potent inhibitor, thiourea (IC₅₀ = 21.5 µM).

Synthesis, characterization and anticancer activity of Fe(II) and Fe(III) complexes containing N-(8-quinolyl)salicylaldimine Schiff base ligands

A series of Fe(II) complexes (1-4) and Fe(III) complexes (5-8) from Fe(II)/(III) chloride and N-(8-quinolyl)-X-salicylaldimine Schiff base ligands (Hqsal-X2/X: X = Br, Cl) were successfully synthesized and characterized by spectroscopic (FT-IR, 1H-NMR), mass spectrometry, thermogravimetric analysis (TGA), and single crystal X-ray crystallographic techniques. The interaction of complexes 1-8 with calf thymus DNA (CT-DNA) was determined by UV-Vis and fluorescence spectroscopy. The complexes exhibited good DNA-binding activity via intercalation. The molecular docking between a selected complex and DNA was also investigated. The in vitro anticancer activity of the Schiff base ligands and their complexes were screened against the A549 human lung adenocarcinoma cell line. The complexes showed anticancer activity toward A549 cancer cells while the free ligands and iron chloride salts showed no inhibitory effects at 100 µM. In this series, complex [Fe(qsal-Cl2)2]Cl 6 showed the highest anticancer activity aginst A549 cells (IC50 = 10 µM). This is better than two well-known anticancer agents (Etoposide and Cisplatin). Furthermore, the possible mechanism for complexes 1-8 penetrating A549 cells through intracellular ROS generation was investigated. The complexes containing dihalogen substituents 1, 2, 5, and 6 can increase ROS in A549 cells, leading to DNA or macromolecular damage and cell-death induction.

Synthesis and Cytotoxic Activity of Novel Metal Complexes Derived from Methyl-3-(4-chlorophenyl)-3-hydroxy-2,2-dimethylpropanoate as Potential CDK8 Kinase Inhibitors

Several metal complexes of methyl-3-(4-chlorophenyl)-3-hydroxy-2,2-dimethylpropanoate derivatives were synthesized and tested for their anti-tumor activities. The ligands include 3-(4-chlorophenyl)-3-hydroxy-2,2-dimethylpropanoic acid (1), 3-(4-chlorophenyl)-3-hydroxy-2,2-dimethylpropanehydrazide (2), and 3-(4-chlorophenyl)-N'-(4-(dimethylamino)benzylidene)-3-hydroxy-2,2-dimethylpropanehydrazide (3). The ligands were reacted with Cu (II), Ni (II), and La (III) ions. The formed complexes were characterized using elemental analysis (M%), molar conductivity in DMF (0.001 M), DTA, TG, FTIR, ICP-AES, and magnetic susceptibility. The chemical structures of the obtained complexes were interpreted, and their chemical formulas were postulated. The anti-cancer activities of these complexes were examined on human colorectal carcinoma cells (HCT-116) and also on normal cells (HEK-293). The 48 h post treatments showed that out of 12 compounds, 10 compounds showed inhibitory actions on HCT-116 cells, whereas two compounds did not show any inhibitory actions. Compounds 6c and 4a showed the highest inhibitory actions with IC50 = 0.154 and 0.18 mM and additionally compounds 3, 4b, and 6a with IC50 = 0.267, 0.205, and 0.284 mM, respectively. All tested compounds did not show any inhibitory action on normal HEK-293 cells. Molecular docking results provided a good evidence for activity of the lead compounds 3 and 4a as CDK8-CYCC kinase inhibitors, which may proposed the mechanism of action toward colon cancer therapy.

Sonication-assisted synthesis of a new heterostructured schiff base ligand Silver-Guar gum encapsulated nanocomposite as a visible light photocatalyst

A heterostructured Schiff base ligand (Benzildiethylenetriamine)-Silver-Guar gum encapsulated nanocomposites was intended to prepare by simple sonication assisted reflux method. Appropriate composition of purified guar gum, Schiff base ligand and silver nitrate were used for the synthesis. The synthesised nanocomposites were characterised by photoluminescence spectrum, UV-vis diffuse reflectance spectrophotometer, Fourier transform infra-red spectroscopy, X-ray diffractometer, scanning electron microscopy and transmission electron microscopy. The crystalline peaks of XRD and FTIR reveals that Schiff base ligand and guar gum forms metal-organic matrix. Morphology studies have confirmed the organic framework structure and metallic silver nanoparticles are embedded on the organic framework. The efficiency of nanocomposites depends on adsorption capacity and silver nanoparticles that are encapsulated thereby increasing the visible light absorption through surface plasma resonance. The nanocomposite was proved to be highly selective in hydrogenation reaction which favoured the formation of aniline from nitrobenzene as single product with short reaction time and 90% conversion.

DNA and HSA interaction of Vanadium (IV), Copper (II), and Zinc (II) complexes derived from an asymmetric bidentate Schiff-base ligand: multi spectroscopic, viscosity measurements, molecular docking, and ONIOM studies

The interaction of three complexes [Zn(II), Cu(II), and V(IV)] derived from an asymmetric bidentate Schiff-base ligand with DNA and HSA was studied using fluorescence quenching, UV-Vis spectroscopy, viscosity measurements, and computational methods [molecular docking and our Own N-layered Integrated molecular Orbital and molecular Mechanics (ONIOM)]. The obtained results revealed that the DNA and HSA affinities for binding of the synthesized compounds follow as V(IV) > Zn(II) > Cu(II) and Zn(II) > V(IV) > Cu(II), respectively. The distance between these compounds and HSA was obtained based on the Förster's theory of non-radiative energy transfer. Furthermore, computational molecular docking was carried out to investigate the DNA- and HSA-binding pose of the compounds. Molecular docking calculations showed that H-bond, hydrophobic, and π-cation interactions have dominant role in stability of the compound-HSA complexes. ONIOM method was utilized to investigate the HSA binding of the compounds more precisely in which molecular-mechanics method (UFF) and semi-empirical method (PM6) were selected for the low layer and the high layer, respectively. The results show that the structural parameters of the compounds changed along with binding, indicating the strong interaction between the compounds with HSA and DNA. Viscosity measurements as well as computational docking data suggest that all metal complexes interact with DNA, presumably by groove-binding mechanism.

Density functionalized [RuII(NO)(Salen)(Cl)] complex: Computational photodynamics and in vitro anticancer facets

Photodynamic therapy (PDT) is a treatment that uses photosensitizing agents to kill cancer cells. Scientific community has been eager for decades to design an efficient PDT drug. Under such purview, the current report deals with the computational photodynamic behavior of ruthenium(II) nitrosyl complex containing N, N'-salicyldehyde-ethylenediimine (SalenH₂), the synthesis and X-ray crystallography of which is already known [Ref. 38,39]. Gaussian 09W software package was employed to carry out the density functional (DFT) studies. DFT calculations with Becke-3-Lee-Yang-Parr (B3LYP)/Los Alamos National Laboratory 2 Double Z (LanL2DZ) specified for Ru atom and B3LYP/6-31G(d,p) combination for all other atoms were used using effective core potential method. Both, the ground and excited states of the complex were evolved. Some known photosensitizers were compared with the target complex. Pthalocyanine and porphyrin derivatives were the compounds selected for the respective comparative study. It is suggested that effective photoactivity was found due to the presence of ruthenium core in the model complex. In addition to the evaluation of theoretical aspects in vitro anticancer aspects against COLO-205 human cancer cells have also been carried out with regard to the complex. More emphasis was laid to extrapolate DFT to depict the chemical power of the target compound to release nitric oxide. A promising visible light triggered nitric oxide releasing power of the compound has been inferred. In vitro antiproliferative studies of [RuCl₃(PPh₃)₃] and [Ru(NO)(Salen)(Cl)] have revealed the model complex as an excellent anticancer agent. From IC₅₀ values of 40.031mg/mL in former and of 9.74mg/mL in latter, it is established that latter bears more anticancer potentiality. From overall study the DFT based structural elucidation and the efficiency of NO, Ru and Salen co-ligands has shown promising drug delivery property and a good candidacy for both chemotherapy as well as light therapy.

Two new heterodinuclear Schiff base complexes: synthesis, crystal structure and thermal studies

Two new heterodinuclear Schiff base complexes, [Hg(L)NiCl2(DMF)2] 1, and [Zn(L)NiCl2(DMF)2] 2, where H2L = N,N'-bis(salicylidene)-1,3-diaminopropane and DMF = dimethylformamide have been synthesized and characterized using elemental analysis, IR spectroscopy, thermal analysis and X-ray diffraction. Structural studies on 1 and 2 reveal the presence of a heterodinuclear [Ni(II)Hg(II)] unit and [Zn(II)Ni(II)] in which the central metal ions are connected to each other by two phenolate oxygen bridges. For complex 1 the Ni(II) ion adopts an elongated octahedral geometry (NiN2O4) while the Hg(II) ion assumes a distorted tetrahedral arrangement (HgO2Cl2) whereas for complex 2 the Zn(II) ion adopts an elongated octahedral geometry (ZnN2O4) while the Ni(II) ion assumes a distorted tetrahedral arrangement (NiO2Cl2). There are intermolecular C-H···Cl-M interactions among the dinuclear complexes which are interconnected for 1 and 2. These intermolecular interactions result in the formation of a three dimensional structure for 1 and one dimensional zig-zag chains for 2.