Synthesis, spectroscopic, thermal and molecular modeling studies of Zn 2+ , Cd 2+ and UO 2 2+ complexes of Schiff bases containing triazole moiety. Antimicrobial, anticancer, antioxidant and DNA binding studies

Advances in Coordination Chemistry of Schiff Base Complexes: A Journey from Nanoarchitectonic Design to Biomedical Applications

Since the discovery of Schiff bases over one and a half centuries ago, there has been tremendous research activity in the design of various Schiff bases and examination of their diverse structures and versatile applications. This family of compounds has continued to captivate many research groups due to the simplicity of their synthesis through the condensation of amines with carbonyl compounds. While conventional synthesis has been the most widely used, green synthetic methodologies have been also explored for this reaction, including sonication, microwave-assisted, natural acid-catalyzed and mechanochemical syntheses as well as utilizing ionic liquid solvents or deep eutectic solvents. Schiff bases have been utilized as excellent ligands for coordination to transition metals and late transition metals (lanthanides and actinides). These Schiff base compounds can be mono-, di-, or polydentate ligands. The aim of this review is to examine the biological applications of Schiff base complexes over the past decade with particular focus on their antimicrobial, antiviral, anticancer, antidiabetic, and anti-inflammatory activity. Schiff base complexes have been found effective in combating bacterial and fungal infections with numerous examples in the literature. The review addressed this area by focusing on the very recent examples while using tables to summarize the vast breadth of research according to the metallic moieties. Viruses have continued to be a target of many researchers in light of their continuous mutations and impact on human health, and therefore some examples of Schiff base complexes with antiviral activity are described. Cancer continues to be among the leading causes of death worldwide. In this article, the use of Schiff base complexes for, and the mechanisms associated with, their anticancer activity are highlighted. The production of reactive oxygen species (ROS) or intercalation with DNA base pairs leading to cell cycle arrest were the main mechanisms described. While there have been some efforts made to use Schiff base complexes as antidiabetic or anti-inflammatory agents, there are limited examples when compared with antimicrobial and anticancer studies. The conclusion of this review highlights the emerging areas of research and future perspectives with an emphasis on the potential uses of Schiff bases in the treatment of infectious and noninfectious diseases.

Synthesis and characterization of novel uranyl clusters supported by bis(pyrazolyl) methane ligands: biomimetic catalytic oxidation, BSA protein interaction and cytotoxicity studies

Two novel uranyl complexes were synthesized using bis-pyrazolyl methane ligands. The complexes were characterized by several spectroscopic techniques, including UV-Vis, IR, NMR, mass spectrometry, fluorescence, electrochemical, and thermogravimetric analysis. The solid-state structure of the complex C1 was determined with the help of single-crystal X-ray diffraction studies. The complexes C1 and C2 efficiently catalyse the oxidation of 3,5-di-tert-butyl catechol and 2-aminophenol in the atmospheric air, imitating the catalytic activity of the catechol oxidase and phenoxazinone synthase enzymes. The kinetic parameters and the catalytic efficiency (K cat/K M) of the reactions were calculated. Formation of organic free radicals in the catalytic reactions was confirmed by EPR spectroscopy. The interaction of these complexes with the protein, bovine serum albumin, was investigated by using UV-Vis and fluorescence spectral analysis. The cytotoxicity of the complexes against MDAMB-231 and A549 cell lines was investigated, and IC50 values were determined.

A Treatise on Furan Cored Schiff Base Cu(II), Ni(II) and Co(III) Complexes Accentuating Their Biological Efficacy: Synthesis, Thermal and Spectroscopic Characterization, DNA Interactions, Antioxidant and Antibacterial Activity Studies

Three metal complexes [Cu(FMIMDIP)₂ ] (1), [Ni(FMIMDIP)₂ ] (2) and [Co(FMIMDIP)₃ ] (3) where, FMIMDIP=(((furan-2-yl)methylimino)methyl)-4,6-diiodophenol, were synthesized and characterized by various spectroscopy. The analytical data revealed a square planar geometry for 1 and 2 and an octahedral geometry for 3. The kinetic and thermodynamic parameters of the thermal decomposition steps were calculated from the thermograms. The quantum chemical parameters have been calculated using HOMO-LUMO energies and reveal the stability of the complexes. The DNA interaction of 1-3 towards calf-thymus DNA was investigated by absorption titration, fluorescence spectroscopy and gel electrophoresis. All the complexes bind to DNA via intercalation mode with binding constant (K_b ) values of 4.17×10³  M^-1 to 5.9×10⁴  M^-1 and also effectively cleave pBR322 DNA by oxidative and photolytic techniques. The synergistic action of metal chelates with ascorbic acid induced the generation of free radicals. The antibacterial activity of 1-3 was tested against B. thuringiensis, S. pneumoniae, E. coli, and P. putida. Complex 3 has the best activity among all the complexes.

Dual role of cadmium in rat liver: Inducing liver injury and inhibiting the progression of early liver cancer

The heavy metal cadmium (Cd) can induce damage in liver and liver cancer cells; however, the mechanism underlying its toxicity needs to be further verified in vivo. We daily administered CdCl2 to adult male rats at different dosages via gavage for 12 weeks and established rat liver injury model and liver cancer model to study the dual role of Cd in rat liver. Increased exposure to Cd resulted in abnormal liver function indicators, pathological degeneration, rat liver cell necrosis, and proliferation of collagen fibres. Using immunohistochemistry, we found that the area of GST-P-positive precancerous liver lesions decreased in a dose-dependent manner. Real-time quantitative polymerase chain reaction, western blot, immunohistochemistry, and transmission electron microscopy revealed that Cd induced mitophagy, as well as mitophagy blockade, as evidenced by the downregulation of TOMM20 and upregulation of LC3II and P62 with increasing Cd dose. Next, the expression of PINK1/Parkin, a classic signalling pathway protein that regulates mitophagy, was examined. Cd was found to promote PINK1/Parkin expression, which was proportional to the Cd dose. In conclusion, Cd activates PINK1/Parkin-mediated mitophagy in a dose-dependent manner. Mitophagy blockade likely aggravates Cd toxicity, leading to the dual role of inducing liver injury and inhibiting the progression of early liver cancer.

Highlights on selected growth factors and their receptors as promising anticancer drug targets

Growth factor receptors (GFRs) and receptor tyrosine kinases (RTK) are groups of proteins mediating a plethora of physiological processes, including cell growth, proliferation, survival, differentiation and migration. Under certain circumstances, expression of GFRs and subsequently their downstream kinase signaling are deregulated by genetic, epigenetic, and somatic changes leading to uncontrolled cell division in many human diseases, most notably cancer. Cancer cells rely on growth factors to sustain the increasing need to cell division and metabolic reprogramming through cancer-associated activating mutations of their receptors (i.e., GFRs). In this review, we highlight the recent advances of selected GFRs and their ligands (growth factors) in cancer with emphasis on structural and functional differences. We also interrogate how overexpression and/or hyperactivation of GFRs contribute to cancer initiation, development, progression, and resistance to conventional chemo- and radiotherapies. Novel approaches are being developed as anticancer agents to target growth factor receptors and their signaling pathways in different cancers. Here, we illustrate how the current knowledge of GFRs biology, and their ligands lead to development of targeted therapies to inhibit and/or block the activity of growth factors, GFRs and downstream kinases to treat diseases such as cancer.

Synthesis of Some Novel Nanosized Chelates of Anchoring Bisazo Dye 5-[5-(4,6-Dioxo-2-thioxo-hexahydro-pyrimidin-5-ylazo)-naphthalen-1-ylazo]-2-mercapto-1H-pyrimidine-4,6-dione and Their Applications as Antioxidant and Antitumor Agents

A novel bisazo 5-[5-(4,6-dioxo-2-thioxo-hexahydro-pyrimidin-5-ylazo)-naphthalen-1-ylazo]-2-mercapto-1H-pyrimidine-4,6-dione (H4L) ligand has been synthesized from diazotization coupling between naphthalene-1,5-diamine and 2-thiobarbituric acid. Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Fe(III) chelates were prepared. All prepared compounds were characterized by different techniques. The azo groups did not participate in chelation according to the infrared spectra, whereas the thioamide group did participate. The azo dye ligand coordinated with all metallic ions in a neutral-keto-thiol structure and behaved as a bi- and tridentate moiety. Zinc, manganese, and iron chelates had an octahedral structure, while nickel and cobalt chelates had a tetrahedral structure, but the copper chelate had a square pyramidal geometry. The thermal behavior of all prepared compounds was investigated and thermokinetic parameters were also discussed. X-ray diffraction (XRD) data reflected that Fe(III) and Zn(II) complexes were crystalline while the Cu(II) complex was amorphous. Calcination of the Fe(III) complex at 600 °C yielded a nanosized Fe2O3 crystalline phase, elucidated by XRD and transmission electron microscope. The novel azo dye and some of its chelates were tested against HepG-2. The Fe2O3 nanooxide showed remarkable activity against the HepG-2 cell line rather than its precursor Fe(III) complex. Co(II) had a higher antioxidant activity than the other investigated complexes. In both activities, the Cu(II) complex did not show any activity. Molecular modeling and some theoretical studies were validated, and the experimental results were interpreted.

Facile synthesis, spectroscopic evaluation and antimicrobial screening of metal endowed triazole compounds

The scientific interest in developing new complexes as inhibitors of bacterial biofilm related infections is constantly rising. The present work describes the chemical synthesis, structural and biological scrutiny of a triazole Schiff base ligand and its corresponding complexes. Triazole Schiff base, (2-methoxy-4-[(1H-1,2,4-triazol-3-ylimino)methyl]phenol) was synthesized from the condensation reaction of 3-amino-1,2,4-triazole and 4-hydroxy-3-methoxybenzaldehyde in an equimolar ratio. The triazole ligand (H₂L) was characterized by physical (solubility, color, melting point), spectroscopic [UV-visible (UV-Vis), Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (¹H-NMR) and mass spectra (MS)] and micro analysis to evaluate their elemental composition. The bidentate ligand was complexed with transition metal [VO(IV), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II)] in 1:2 molar ratio. The complexes were characterized by physical (color, solubility, decomposition temperature, conductance and magnetic moment), FT-IR, UV-Vis and elemental analysis. Thermal stability and fluorescence properties of the compounds were also determined. Density functional theory based theoretical calculations were accomplished to gain more insight into spectroscopic properties. The frontier molecular orbital analysis revealed that the ligand was less reactive with reduced electron donating capability and more kinetic stability than complexes. The as-synthesized compounds were scrutinized for anti-bacterial and anti-fungal activity against selected strains. Cobalt complex exhibited highest antibacterial activity against Escherichia coli and nickel complex has shown highest antifungal activity against Aspergillus niger. All the compounds also showed good antioxidant activity. The theoretical results reflect consistency with the experimental findings signifying that such compounds could be the promising chemical scaffolds in the near future against microbial infectious.

Complexation of uranyl (UO2)2+ with bidentate ligands: XRD, spectroscopic, computational, and biological studies

Three new uranyl complexes [(UO₂)(OAc)₂(CMZ)], [(UO₂)(OAc)₂(MP)] and [(UO₂)(OAc)₂(SCZ)] were synthesized and characterized by elemental analysis, FT-IR, UV-Vis spectroscopy, powder XRD analysis, and molar conductivity. The IR analysis confirmed binding to the metal ion by the sulfur and ethoxy oxygen atoms in the carbimazole (CMZ) ligand, while in the 6-mercaptopurine (MP) ligand, the sulfur and the N7 nitrogen atom of a purine coordinated binding to the metal ion. The third ligand showed a 1:1 molar ratio and bound via sulfonamide oxygen and the nitrogen of the pyrimidine ring. Analysis of the synthesized complexes also showed that acetate groups had monodentate binding to the (UO₂²⁺). Density Functional Theory (DFT) calculations at the B3LYP level showed similar structures to the experimental results. Theoretical quantum parameters predicted the reactivity of the complexes in the order, [(UO₂)(OAc)₂(SCZ)] > [(UO₂)(OAc)₂(MP)]> [(UO₂)(OAc)₂(CMZ)]. DNA binding studies revealed that [(UO₂)(OAc)₂(SCZ)] and [(UO₂)(OAc)₂(CMZ)] have the highest binding constant (K_b) among the uranyl complexes. Additionally, strong binding of the MP and CMZ metal complexes to human serum albumin (HSA) were observed by both absorbance and fluorescence approaches. The antibacterial activity of the complexes was also evaluated against four bacterial strains: two gram-negative; Escherichia coli and Klebsiella pneumonia, and two gram-positive; Staphylococcus aureus and Streptococcus mutans. [(UO₂)(OAc)₂(MP)] had the greatest antibacterial activity against Klebsiella pneumonia, the gram-positive bacteria, with even higher activity than the standard antibiotic. In vitro cytotoxicity tests were also performed against three human cancer lines, and revealed the most cytotoxic complexes to be [(UO₂)(OAc)₂(SCZ)], which showed moderate activity against a colon cancer cell line. Thus, uranyl addition enhances the antibacterial and anticancer properties of the free ligands.

Discovery of metal-based complexes as promising antimicrobial agents

The antimicrobial resistance (AMR) is an intractable problem for the world. Metal ions are essential for the cell process and biological function in microorganisms. Many metal-based complexes with the potential for releasing ions are more likely to be absorbed for their higher lipid solubility. Hence, this review highlights the clinical potential of organometallic compounds for the treatment of infections caused by bacteria or fungi in recent five years. The common scaffolds, including antimicrobial peptides, N-heterocyclic carbenes, Schiff bases, photosensitive-grand-cycle skeleton structures, aliphatic amines-based ligands, and special metal-based complexes are summarized here. We also discuss their therapeutic targets and the risks that should be paid attention to in the future studies, aiming to provide information for researchers on metal-based complexes as antimicrobial agents and inspire the design and synthesis of new antimicrobial drugs.

A review: Pharmacological aspects of metal based 1,2,4-triazole derived Schiff bases

Clinical reports have highlighted the radical increase of antibiotic resistance. As a result, multidrug resistance has emerged as a serious threat to human health. Many organic compounds commonly used as drugs in the past, no longer have pure organic mode of action rather need bio-transformation or more activation. Bulk of research has shown that they need trace amount of metal ions incorporated within the chemistry of bioactive molecules for enhancement of their potentiality to fight aggressively against resistance. The deficiency of some metal ions can also be responsible for many diseases like growth retardation, pernicious anemia and heart diseases in infants. To overcome these problems, there is a need to introduce novel strategies which have new mechanism of action along with significant spectrum of biological activity, enhanced safety and efficacy. Bioinorganic compounds have played imperative role in developing the new strategy in the form of "Metal Based Drugs". In current years there have been momentous rise of interest in the application of metal based Schiff base compounds to treat various diseases which are difficult to be treated with conventional methodologies. The unique properties of metal chelates acting as an intermediate between conventional organic and inorganic compounds provided innovative opportunities in the field of pharmaceutical chemistry. In this review, we have exclusively focused on the search of metal based 1,2,4-triazole derived Schiff base compounds (synthesized, reported and reviewed in the past ten years) that possess various biological activities such as antifungal, antibacterial, antioxidant, antidiabetic, anthelmintic, anticancer, antiproliferative, cytotoxic and DNA-intercalation activity.

Structural investigation, DNA interactions and in vitro anticancer studies of transition metal complexes of 3-(2-(2, 4-dihydroxy benzylidene) hydrazinyl) quinoxalin-2(1H) -one

The Schiff base ligand, 3-(2-(2, 4-dihydroxybenzylidene) hydrazinyl) quinoxalin-2(1H)-one (RHQO) has been synthesized and characterized by spectral and single crystal X-ray analysis. The Mn(II), Ni(II) and Cu(II) complexes of RHQO have been synthesized and characterized by FT-IR, UV-VIS, mass, EPR spectra, CHN, thermo gravimetric analysis, magnetic susceptibility and conductivity measurements. The morphology of the ligand and complexes is studied by Scanning Electron Microscopy. The metal complexes formed were found to be polymeric in nature. The abilities of the ligand and its metal complexes to interact and bind with calf thymus DNA (CT-DNA) has been studied by electronic absorption spectroscopy and their quantitative binding strength was evaluated in terms of their intrinsic binding constant (K_b). The cleavage interaction of the ligand and its metal complexes with super coiled pBR 322 DNA has been investigated by agarose gel electrophoresis. Cytotoxicity of the Cu(II) and Ni(II) complexes was evaluated using various cancer cell lines, Human cervical cancer cell line (Hela), B16 melanoma F10(B16-F10), Human ovarian cancer cell (SKOV3) and Breast cancer cell line (MCF7) by MTT assay. The results indicated that the ligand and its metal complexes bind with CT-DNA by groove binding mode and cleaved the supercoiled pBR 322 DNA in to nicked form. The Ni(II) and Cu(II) complexes exhibited anticancer activity without affecting the normal CHO-K1 cell lines. Communicated by Vsevolod Makeev.

A novel fluorescence sensor for relay recognition of zinc ions and nitric oxide through fluorescence ‘off–on–off’ functionality

The fluorescent ‘off–on–off’ probe for relay recognition of Zn²⁺ and nitro oxide (NO) was constructed with the detection limit of 10⁻⁸ mol L⁻¹.

Rosa NM, Costa LAS, Visbal G, Rozental S, Navarro M. Synthesis, characterization and biological evaluation of zinc and copper azasterol complexes against Sporothrix brasiliensis

Characterized zinc– and copper–azasterol complexes acting as promising antifungal agents against Sporothrix brasiliensis. Metal–drug synergism was effectively applied.

New Heteroleptic 3D Metal Complexes: Synthesis, Antimicrobial and Solubilization Parameters

The microbial resistance to current antibiotics is increasing day by day, which in turn accelerating the development of new effective drugs. Several studies have proved the high antimicrobial potential of the interaction of several organic ligands with a variety of metal ions. In the present study, a conventional method has been adopted in the synthesis of twelve new heteroleptic complexes of cobalt (II), nickel (II), copper (II) and zinc (II) using three aldimines, namely, (HL₁ ((E)-2-((4-chloro-2-hydroxybenzylidene)amino)-3,4-dimethyl-5-phenylcyclopent-2-en-1-one), HL₂ ((Z)-3-((4-chlorobenzylidene)amino)-4-hydroxy-5-nitrobenzenesulfonic acid) HL₃ (2,2'-((1,2-phenylenebis(azaneylylidene))bis(methaneylylidene))diphenol)) as primary ligands, while phenyl glycine was the secondary ligand. The synthesized compounds were characterized by UV-vis, IR and multinuclear (¹H and ¹³C) NMR spectroscopy, elemental analysis, and electrical conductance. The IR study revealed the coordination of the aldimine derivatives with the -OH and N atom of imine moiety. In contrary to this, the phenyl glycine coordinated to the metal ions via oxygen of carboxylate and nitrogen of the amino group. The spectroscopic analysis unveiled the tetrahedral geometry of the synthesized metal (II) complexes, except for ligand HL₃ which exhibited octahedral geometry. The synthesized compounds generally showed antibacterial activity for all microbes, except Ni (II) complexes lacking sensitivity. Furthermore, to access the bioavailability, the synthesized complexes were screened for their solubilization in the micellar media of sodium lauryl sulphate. The metal complex-surfactant interaction was revealed by UV-vis spectroscopy and electrical conductivity measurements.

Copper(ii) and zinc(ii) complexes of mono- and bis-1,2,3-triazole-substituted heterocyclic ligands

Chelating 1,4-disubstituted mono- (8a-8d) and bis-1,2,3-triazole-based (9a-11a) ligands were prepared by regioselective copper(i)-catalysed 1,3-dipolar cycloaddition of terminal alkynes with aromatic azides, together with bioconjugate 13a synthesized by amide coupling of l-phenylalanine methyl ester to 11a. Cu(ii) and Zn(ii) complexes were prepared and single crystal structures were determined for complexes 8aCu, 8dCu, 9cCu and 10cCu, as well as the free ligands 10a and 10c. The in situ prepared Zn(ii) complexes were studied by NMR spectroscopy, while the stoichiometry of the Cu(ii) complexes in solution was determined by UV-Vis titrations and confirmed by the electronic structure DFT calculations at the (SMD)/M05-2X/6-31+G(d)/LanL2DZ+ECP level of theory.

Transition Metal Complexes of (E)‐2((2‐hydroxybenzylidene) amino‐3‐mercaptopropanoic acid: XRD, Anticancer, Molecular modeling and Molecular Docking Studies

The anticancer studies of a Schiff base; (E)‐2((2‐hydroxybenzylidene)amino‐3‐mercaptopropanoic acid (H2L) (obtained from 2‐hydroxybenzaldehyde and L‐cysteine) and its transition metal complexes have been reported. The evaluation of the growth inhibitory action was studied for the compounds against human colon carcinoma (HCT‐116), human hepatocellular liver carcinoma (HEPG‐2), normal melanocytes (HFB‐4) and human breast carcinoma (MCF‐7) cell lines. The obtained results revealed that the Schiff base and its chelates are active against human hepatocellular liver carcinoma (HEPG‐2) cell lines. The powder X‐ray diffraction analysis for the compounds was carried out through Phillips X′Pert High score software. The density functional theory computation for ligand and Co(II), Ni(II) and Cu(II) metal complexes were made to understand the mode of bonding by GAUSSIAN 03 rev. A.01 programme. The quantitative structure‐activity relationship investigation was performed by using HyperChem Professional 8.0.3 software to understand the biological potency of the ligands. Moreover, a docking analysis using iGEMDOCKv2.1 software was carried out against the kinase enzyme PDB ID:1fvv.

In silico and in vitro studies of transition metal complexes derived from curcumin-isoniazid Schiff base

A series of transition metal complexes have been synthesized from biologically active curcumin and isoniazid Schiff base. They are characterized by various spectral techniques like UV-Vis, Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and mass spectroscopies. Moreover, elemental analysis, magnetic susceptibility and molar conductivity measurements are also carried out. All these data evidence that the metal complexes acquire square planar except zinc(II) which adopts a tetrahedral geometry, and they are non-electrolytic in nature. Groove mode of binding between the calf thymus DNA (CT DNA) and metal complexes is confirmed by electronic absorption titration, viscosity and cyclic voltammetry studies. In addition to that, all the metal complexes are able to cleave pUC 19 DNA. Optimized geometry and ground-state electronic structure calculations of all the synthesized compounds are established out by density functional theory (DFT) using B3LYP method which theoretically reveals that copper(II) complex explores higher stability and higher biological accessibility. This is experimentally corroborated by antimicrobial studies. In silico Absorption, Distribution, Metabolism, Excretion (ADME) studies reveal the biological potential of all synthesized complexes, and also biological activity of the ligand is predicted by PASS online biological activity prediction software. Molecular docking studies are also carried out to confirm the groove mode of binding and receptor-complex interactions.