Synthesis, characterization and biological activity of some transition metals with Schiff base derived from 2-thiophene carboxaldehyde and aminobenzoic acid

New nano-complexes targeting protein 3S7S in breast cancer and protein 4OO6 in liver cancer investigated in cell line

Cancer, a lethal ailment, possesses a multitude of therapeutic alternatives to combat its presence, metal complexes have emerged as significant classes of medicinal compounds, exhibiting considerable biological efficacy, especially as anticancer agents. The utilization of cis-platin in the treatment of various cancer types, including breast cancer, has served as inspiration to devise novel nanostructured metal complexes for breast cancer therapy. Notably, homo- and hetero-octahedral bimetallic complexes of an innovative multifunctional ether ligand (comprising Mn(II), Ni(II), Cu(II), Zn(II), Hg(II), and Ag(I) ions) have been synthesized. To ascertain their structural characteristics, elemental and spectral analyses, encompassing IR, UV-Vis, 1H-NMR, mass and electron spin resonance (ESR) spectra, magnetic moments, molar conductance, thermal analysis, and electron microscopy, were employed. The molar conductance of these complexes in DMF demonstrated a non-electrolytic nature. Nanostructured forms of the complexes were identified through electron microscopic data. At ambient temperature, the ESR spectra of the solid complexes exhibited anisotropic and isotropic variants, indicative of covalent bonding. The ligand and several of its metal complexes were subjected to cytotoxicity testing against breast cancer protein 3S7S and liver cancer protein 4OO6, with the Ag(I) complex (7) evincing the most potent effect, followed by the Cu(II) with ligand (complex (2)), Cis-platin, the ligand itself, and the Cu(II)/Zn(II) complex (8). Molecular docking data unveiled the inhibitory order of several complexes.

Insight into the inhibitory potential of metal complexes supported by (E)-2-morpholino-N-(thiophen-2-ylmethylene)ethanamine: synthesis, structural properties, biological evaluation and docking studies

A thiophene-derived Schiff base ligand (E)-2-morpholino-N-(thiophen-2-ylmethylene)ethanamine was used for the synthesis of M(II) complexes, [TEM(M)X2] (M = Co, Cu, Zn; X = Cl; M = Cd, X = Br). Structural characterization of the synthesized complexes revealed distorted tetrahedral geometry around the M(II) center. In vitro investigation of the synthesized ligand and its M(II) complexes showed considerable anti-urease and leishmanicidal potential. The synthesized complexes also exhibited a significant inhibitory effect on urease, with IC50 values in the range of 3.50-8.05 μM. In addition, the docking results were consistent with the experimental results. A preliminary study of human colorectal cancer (HCT), hepatic cancer (HepG2), and breast cancer (MCF-7) cell lines showed marked anticancer activities of these complexes.

New Cu(II), Mn(II) and Mn(III) Schiff base complexes cause noncovalent interactions: X-ray crystallography survey, Hirshfeld surface analysis and molecular simulation investigation against SARS-CoV-2

In this study, polynuclear Cu(II) complex (1), Mn(II) and Mn(III) complex (2) have been prepared with a Schiff base ligand derived from 2-Hydroxy-3-methoxybenzaldehyde with 2-amino-2-methyl-1-propanol. The compounds were characterized by elemental analysis, FT-IR, and UV-Vis spectroscopy. The molecular and crystal structures of (1-2) were determined by the single-crystal x-ray diffraction technique. It turned out that Cu(II) complex (1) forms an S₄ -symmetrical tetrameric cage structure, with square-planar coordinated Cu and bridging O atoms at the vertexes of the approximate cube. In the crystal structure of 1, there are large channels along the c-axis, between the tetramers; the solvent- DMSO molecules, occupies these channels. In turn, the complex (2) creates a centrosymmetric trimeric structure, with three octahedrally coordinated Mn ions bridged by O atoms from ligand molecules and acetate ions. The electrochemical behavior studies of the complexes in DMSO displayed the electronic effects of the groups on the redox potential. The redox behavior of Schiff base (1) and (2) complexes included quasi -reversible and irreversible voltammograms, respectively. Intermolecular interactions in the solid states were studied by Hirshfeld surface analysis. These studies provide a comprehensive description of these inter-contact exchanges using an attractive graphical representation using Hirshfeld surfaces and fingerprint plots, along with enrichment ratios. Furthermore, assessment of the inhibitory effect against coronavirus (main protease SARS-CoV-2) was performed by a molecular docking study for both complexes (1 and 2). Both complexes showed a good affinity for CoV-2 for PDB protein ID: 6M03 and 6Y2F.

In vitro and in silico study of the biological activity of tetradentate Schiff base copper(II) complexes with ethylenediamine-bridge

The biological activity of six structurally similar tetradentate Schiff base copper(II) complexes, namely [Cu(ethylenediamine-bis-acetylacetonate)] (CuAA) and five derivatives where two methyl groups are replaced by phenyl, (CuPP), CF3 (CuTT) or by mixed groups CH3/CF3 (CuAT), Ph/CF3 (CuPT), and Ph/CH3 (CuAP) has been investigated. The set of antioxidant assays was performed, and the results were expressed as IC₅₀ and EC₅₀ values. The series of complexes showed interesting bioactivity and were investigated for the determination of antioxidant, antifungal, antimicrobial, and cytotoxic activity. A significant antioxidant behavior was exhibited by complex CuAA, greater than Trolox in the Oxygen Radical Absorbance Capacity (ORAC) assay. Antibacterial assay over Gram-positive and Gram-negative pathogenic bacterial strains and some fungal pathogens were studied. Antiproliferative activity of complexes in two human tumor cell lines, breast adenocarcinoma MCF-7, colon adenocarcinoma LS-174, and normal fibroblast cells-MRC-5, examined the effect on cell cycle progression. The significant cytotoxic potential, comparable to cisplatin cytotoxicity, was determined in human breast cancer cell line-MCF-7 with IC₅₀ values being 17.53-31.40 μM and human colon cancer cell line-LS-174 with IC₅₀ values being 15.22-23.92 μM. All tested compounds showed nearly twice more selectivity toward cancer cell lines than normal cells. The interactions of complexes with human serum albumin (HSA), the most prominent protein in plasma, were investigated using spectroscopic fluorescence techniques. The complexes bind to human serum albumin at multiple sites (n = 0.2-1.9), displaying a moderate binding constant K_a = 4.1-12.4 × 10⁴ M^-1. The molecular docking experiment effectively showed complex binding to HSA and DNA molecular fragments.

Synthesis and Characterization of Zinc(II), Cadmium(II), and Palladium(II) Complexes with the Thiophene-Derived Schiff Base Ligand

Zn(II), Pd(II), and Cd(II) complexes, [L _TH MCl ₂ ] (M = Zn, Pd; X = Br, Cl) and [L _TH Cd(μ-X)X] _n (X = Cl, Br; n = n, 2), supported by the (E)-N ¹,N ¹-dimethyl-N ²-(thiophen-2-ylmethylene)ethane-1,2-diamine (L _TH ) ligand are synthesized and structurally characterized. Density functional theory (DFT) electronic structure calculations and variable-temperature NMR support the presence of two conformers and a dynamic interconversion process of the minor conformer to the major one in solution. It is found that the existence of two relevant complex conformers and their respective ratios in solution depend on the central metal ions and counter ions, either Cl^- or Br^-. Among the two relevant conformers, a single conformer is crystallized and X-ray diffraction analysis revealed a distorted tetrahedral geometry for Zn(II) complexes, and a distorted square planar and square pyramidal geometry for Pd(II) and Cd(II) complexes, respectively. It is shown that [L _TH MCl ₂ ]/LiO ⁱ Pr (M = Zn, Pd) and [L _TH Cd(μ-Cl)Cl] _n /LiO ⁱ Pr can effectively catalyze the ring-opening polymerization (ROP) reaction of rac-lactide (rac-LA) with 94% conversion within 30 s with [L _TH ZnCl ₂ ]/LiO ⁱ Pr at 0 °C. Overall, hetero-enriched poly(lactic acid)s (PLAs) were provided by these catalytic systems with [L _TH ZnCl ₂ ]/LiO ⁱ Pr producing PLA with higher heterotactic bias (P _r up to 0.74 at 0 °C).

Development of New Azomethine Metal Chelates Derived from Isatin: DFT and Pharmaceutical Studies

Through the condensation of isatin (indoline-2, 3-dione) and aniline in a 1:1 ratio, a Schiff base ligand was synthesized and characterized via (¹H-NMR, mass, IR, UV-Vis) spectra. Elemental analyses, spectroscopy (¹H-NMR, mass, UV-Vis), magnetic susceptibility, molar conductivity, mass spectra, scanning electron microscope (SEM), and thermal analysis have all been used to characterize a series of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) metal complexes derived from the titled ligand. The metal-to-ligand ratio is 1:1, according to the analytical data. The Schiff base ligand displayed bidentate behavior with NO coordination sites when it bonded to metal ions, as seen by the IR spectra. The magnetic moment measurement and UV-Vis spectral investigation showed the octahedral geometry of the Cr(III), Fe(III), Co(II), Ni(II), and Zn(II) complexes, whereas they suggested the tetrahedral geometry of the Mn(II), Cu(II), and Cd(II) complexes. The thermal analysis study confirmed the presence of both hydrated and coordinated water molecules in all the compounds, except for the Mn(II) complex, and showed that the complexes decomposed in three or five decomposition steps leaving the corresponding metal oxide as a residue. The ligand and its metal complexes' antibacterial efficacy were evaluated. The findings showed that the metal complexes had stronger antibacterial properties than the ligand alone. The ligand and its metal complexes' anticancer properties were also investigated. A DFT investigation is also reported to gather information regarding the electronic features of the ligand and its metal complexes. Finally, drug-likeness and ADME characteristics were also calculated as parameters.

Novel Schiff base scaffolds derived from 4-aminoantipyrine and 2-hydroxy-3-methoxy-5-(phenyldiazenyl)benzaldehyde: Synthesis, antibacterial, antioxidant, and anti-inflammatory

The synthesis of four new azo Schiff base ligands from 2-hydroxy-3-methoxy-5-(phenyldiazenyl)benzaldehyde and 4-aminoantipyrine is described in this study. The molecular structures of all the scaffolds were confirmed using NMR spectroscopies such as ¹ H and ¹³ C, as well as FT-IR and Mass spectroscopy. After successful synthesis and characterization of all the ligands, their In-vitro antibacterial, antioxidant and anti-inflammatory activities were carried out by using standard protocols. Results revealed that all the four ligands (L1-L4) possessed excellent biological potency. This article is protected by copyright. All rights reserved.

Reactivity of Nitric Oxide and Nitrosonium Ion with Copper(II/I) Schiff Base Complexes: Mechanistic Aspects of Imine C═N Bond Cleavage and Oxidation of Pyridine-2-aldehyde to Pyridine-2-carboxylic Acid

Four Schiff base ligands of the general formulas [6-(R)-2-pyridyl-N-(2'-methylthiophenyl)methylenimine] (^RL1) and 6-p-chlorophenyl-2-pyridyl-N-(2'-phenylthiophenyl)methylenimine (^RL2), where R = H, Me, p-ClPh, and their bis-ligand copper(II) and copper(I) complexes, 1-4 and 1'-4', respectively, were synthesized and characterized. The reactivities of 1-4 with nitric oxide (NO) gas and of 1'-4' with solid NOBF₄ (NO⁺) were examined in dry acetonitrile in the presence and absence of water (H₂O). The results revealed that, in the absence of H₂O, complexes 1-4 (or 1'-4') reacts with NO (or NOBF₄), leading to imine C═N bond cleavage of both (or one) Schiff base(s) that generates 2 (or 1) equiv of 2-(methyl/phenyl)thiobenzenediazonium perchlorates (5/6) and the corresponding picolaldehyde (^RPial) via a copper nitrosyl of a {CuNO}¹⁰-type intermediate. In the presence of H₂O, the in situ formed ^RPial get oxidized to the corresponding picolinic acid (^RPicH) via an in situ formed LCu^IOH intermediate (LCu^I + HO-NO → LCu^IOH + NO⁺; L = ^RL1/^RL2/^RPic^- and ν_O-H of Cu^IOH = 3650 cm^-1) and subsequently produces, with the aid of NO⁺ oxidant, the picolinate-ligated copper(II) complexes (i) [(^HPic)₂Cu] (7), [(^MePic)₄Cu₃(NO₃)₂]_n·H₂O (8·H₂O), or [(^ClPhPic)₂Cu] (9) when NO reacts with 1-4 or (ii) [(^RPic)Cu^II(^RL1/^RL2)]⁺ when NO⁺ reacts with 1'-4'. The Cu^II to Cu^I reduction of [(^RPic)Cu^II(^RL1/^RL2)]⁺ is essential for C═N cleavage of the remaining ^RL1/^RL2 Schiff base; excess NO can do it. The X-ray structures (1, 1', 3', 5, 7, and 8) and spectroscopic results revealed the role of Cu^II/I, NO, NO⁺, and H₂O, shedding light on the mechanism of C═N bond cleavage and the oxidation of pyridine-2-aldehyde to pyridine-2-carboxylic acid. The reaction of 1 with ¹⁵NO revealed that the terminal N of the N₂⁺ group of 5 originates from ¹⁵NO [ν_{¹⁴N¹⁴N-} = 2248 cm^-1 and ν_{¹⁵N¹⁴N-} = 2212 cm^-1].

Spectral, Structural, and Antibacterial Study of Copper(II) Complex with N2O2 Donor Schiff Base Ligand and Its Usage in Preparation of CuO Nanoparticles

A new Schiff base complex, Cu(H2L)2 (H3L: 6,6 ${}^{\prime }$ -((1E,1 ${}^{\prime }$ E)-((azanediylbis(ethane-2,1-diyl))bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol)), through the reaction of ligand H3L with Cu(NO3)2 3H2O, in the ratio of 2 : 1 in methanol solvent was prepared. The obtained ligand (H3L) was characterized by FT-IR, 13C NMR, 1H NMR and elemental analyses. Then its copper(II) complex was prepared and characterized by FT-IR spectroscopy, thermal studies, elemental analyses and single crystal X-ray diffraction. The X-ray crystallography revealed that the two H3L ligands in bidentate fashion coordinated to one copper center for producing Cu(H2L)2 complex. We used copper(II) Schiff base complex, Cu(H2L)2, for the preparation of CuO nanoparticles via solid-state thermal decomposition. The crystalline structure of the product was studied by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). XRD indicated that the new product was copper oxide. SEM image showed that the size of CuO nanoparticles was between 46 and 53 nm, and they had uniform shape. The antibacterial properties of the complex and ligand were also investigated. The results revealed that Schiff base complex showed higher biological activity than Schiff base ligand.

N-((1H-Pyrrol-2-yl)methylene)-6-methoxypyridin-3-amine and Its Co(II) and Cu(II) Complexes as Antimicrobial Agents: Chemical Preparation, In Vitro Antimicrobial Evaluation, In Silico Analysis and Computational and Theoretical Chemistry Investigations

Researchers are interested in Schiff bases and their metal complexes because they offer a wide range of applications. The chemistry of Schiff bases of heterocompounds has got a lot of attention because of the metal's ability to coordinate with Schiff base ligands. In the current study, a new bidentate Schiff base ligand, N-((1H-pyrrol-2-yl)methylene)-6-methoxypyridin-3-amine (MPM) has been synthesized by condensing 6-methoxypyridine-3-amine with pyrrole-2-carbaldehyde. Further, MPM is used to prepare Cu(II) and Co(II) metal complexes. Analytical and spectroscopic techniques are used for the structural elucidation of the synthesized compounds. Both MPM and its metal complexes were screened against Escherichia coli, Bacillus subtilis, Staphylococcus aureus and Klebsiella pneumoniae species for antimicrobial studies. Furthermore, these compounds were subjected to in silico studies against bacterial proteins to comprehend their best non-bonded interactions. The results confirmed that the Schiff base ligand show considerably higher binding affinity with good hydrogen bonding and hydrophobic interactions against various tested microbial species. These results were complemented with a report of the Conceptual DFT global reactivity descriptors of the studied compounds together with their biological scores and their ADMET computed parameters.

Potential applicability of Schiff bases and their metal complexes during COVID-19 pandemic – a review

The rapid growth and revolution in the area of emerging therapeutics has been able to save the life of millions of patients globally. Besides these developments, the microbes are consistently struggling for their own survival and hence becoming quite more sturdy and incurable to existing drugs. Covid-19 virus and Black Fungus are recent examples of failure of medical preparations and strength of these viruses beyond the imagination of medical practitioners. Henceforth the study has made an extensive survey of exiting literature on heterocyclic schiff bases and their transition metal complexes to look for their potential applicability as antimicrobial agents. The inherent physiognomies of the essential properties of these transition metal complexes including thermodynamic, kinetic and chelating are comparatively modifiable as per requirements. The study has found that the biological applications of these transition metal complexes are well suited to be used as antibacterial and antifungal agents.

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 of New Naphthyl Aceto Hydrazone-Based Metal Complexes: Micellar Interactions, DNA Binding, Antimicrobial, and Cancer Inhibition Studies

In the present study, naphthyl acetohydrazide (HL) ligand was prepared and used for the synthesis of new six amorphous transition metal (Co(II), Ni(II), Cu(II), Zn(II), Pb(II), Cd(II)) complexes. All the compounds were characterized by elemental analysis, UV-vis, FT-IR, ¹H- and ¹³C-NMR, and Matrix-Assisted Laser Desorption Ionization (MALDI). The solubilization study was carried out by estimating the interaction between the metal complexes with surfactants viz. sodium stearate (SS) and Cetyltrimethylammonium bromide (CTAB). UV-Visible spectroscopy was employed to determine partitioning and binding parameters, whereas electrical conductivity measurements were employed to estimate critical micellar concentration (CMC), the extent of dissociation, and free energy of micellization. The CT-DNA interaction of synthesized compounds with DNA represents the major groove binding. The synthesized ligand and metal complexes were also tested against bacterial and fungal strains and it has been observed that Cu(II) complex is active against all the strains except Candida albicans, while Cd(II) complex is active against all bacterial and fungal strains except Pseudomonas. Among all compounds, only the Pd(II) complex shows reasonable activity against cervical cancer HeLa cell lines, representing 97% inhibition.

Molecular docking, photocatalytic activity and biomedical investigations of some metal complexes

Metal(II)-(furfural-L-his) complexes with a potentially bidentate furfural-L-his have been synthesized. Furfural-L-his and its Co/Ni/Cu/Zn(II)-(furfural-L-his) complexes have been optimized by DFT. The structural features were determined from their elemental analyses, molar conductance, magnetic, UV-Vis, IR, mass, ¹H NMR and EPR spectral studies. On the basis of electronic spectral data and magnetic measurements, suitable geometry has been proposed for each complex. The redox behaviour of Cu(II)-(furfural-L-his) complex has been studied by cyclic voltammetry. Thermal decomposition profiles are consistent with the proposed formulation of Co/Ni/Cu/Zn(II)-(furfural-L-his) complexes. PXRD studies reveal that furfural-L-his and Zn(II)-(furfural-L-his) complex are of nanomeric structure. SEM images of furfural-L-his exhibit flake-like morphology. Photodegradation of methylene blue dye indicates that they are photocatalyticaly efficient. NBO and NPA shown considerable reduction in the formal charge on metal ions. Docking analysis with EGFR and cyclooxygenase-2 receptor has been performed to find the best binding energy. Antimicrobial, antioxidant and anti-inflammatory activity against standard at variable concentrations revealed that the Co/Ni/Cu/Zn(II)-(furfural-L-his) complexes show enhanced antimicrobial, free radical scavenging and anti-inflammatory activities as compared to furfural-L-his. Furfural-L-his and Cu(II)-(furfural-L-his) complex have been tested against human ovarian cancer cells, which showed that Cu(II)-(furfural-L-his) complex exhibited promising anticancer activity.Communicated by Ramaswamy H. Sarma.

Chromium Coordination Compounds with Antimicrobial Activity: Synthetic Routes, Structural Characteristics, and Antibacterial Activity

A major threat to public health worldwide is that the antimicrobial activity of the established drugs is constantly reduced due to the resistance that bacteria develop throughout the years. Some transition metal complexes show higher antibacterial activity against several bacteria compared to those of clinically used antibiotics. Novel classes of molecules provide new challenges and seem promising to solve the crisis that the overuse of antibiotics has led over the last years. This review discusses the challenges of chromium-based metallodrugs as antimicrobial agents. In particular, the synthetic routes, the structural characteristics, as well as the antimicrobial activity of 32 chromium (III) complexes have been presented.

Metal complexes driven from Schiff bases and semicarbazones for biomedical and allied applications: a review

Schiff bases are versatile organic compounds which are widely used and synthesized by condensation reaction of different amino compound with aldehydes or ketones known as imine. Schiff base ligands are considered as privileged ligands as they are simply synthesized by condensation. They show broad range of application in medicine, pharmacy, coordination chemistry, biological activities, industries, food packages, dyes, and polymer and also used as an O2 detector. Semicarbazone is an imine derivative which is derived from condensation of semicarbazide and suitable aldehyde and ketone. Imine ligand-containing transition metal complexes such as copper, zinc, and cadmium have shown to be excellent precursors for synthesis of metal or metal chalcogenide nanoparticles. In recent years, the researchers have attracted enormous attention toward Schiff bases, semicarbazones, thiosemicarbazones, and their metal complexes owing to numerous applications in pharmacology such as antiviral, antifungal, antimicrobial, antimalarial, antituberculosis, anticancer, anti-HIV, catalytic application in oxidation of organic compounds, and nanotechnology. In this review, we summarize the synthesis, structural, biological, and catalytic application of Schiff bases as well as their metal complexes.

Polymer-supported metal catalysts for the heterogeneous polymerisation of lactones

Polymer-supported metal catalysts are used for the heterogeneous polymerisation of renewable lactones, towards the efficient and environmentally benign production of sustainable polymers.