Metallo-Organic Complexes Containing Transition Metals; Synthetic Approaches and Pharmaceutical Aspects

Coordination compounds offer a flexible framework for the thoughtful design of novel therapeutic-metallodrugs because of the unique properties of metal ions, such as their ability to coordinate with a wide range of organic ligands, variable oxidation states, a wide range of geometries, and coordination numbers. The pharmaceutical potential of a metal ion and associated substances is validated by the prevalence of various disease states linked to a metal ion's excess or deficiency within the biological system. Researchers have sought more selective, efficacious metallodrugs that cause fewer adverse effects. Attempts have resulted in considering a large range of organic ligands, preferably polydentate ligands with demonstrated biological activity, and a large range of metals from the periodic table, primarily from the d-block. In this review, we have outlined the key coordination complexes comprising N-, O-, and S-donor ligands reported in the last six years to demonstrate the potential applications of these metallo-organic complexes. The synthetic pathways of ligands, their complexes, and their potential for therapeutic applications are highlighted.

New penta-Coordinated Cadmium(II) Complexes: Synthesis, Characterization, Thermal, Antimicrobial, Antioxidant and Cytotoxicity Properties

In this paper, a new tridentate Schiff base ligand (L) with nitrogen donor atoms and its cadmium(II) complexes with the general formula of CdLX2 (X=Cl-, Br-, I-, SCN-, N3 -, NO3 -) have been synthesized and characterized by physical and spectral (FT/IR, UV-Vis, Mass, and 1H, 13C NMR spectroscopies) methods. Also nano-structured cadmium chloride and bromide complexes were synthesized by sonochemical method and then used to prepare nanostructured cadmium oxide confirmed by XRD and SEM techniques. Thermal behavior of the compounds was studied in the temperature range of 25 to 900 °C under N2 atmosphere at a heating rate of 20 °C/ min. Moreover, thermo-kinetic activation parameters of thermal decomposition steps were calculated according to the Coats-Redfern relationship. Antimicrobial activities of the synthesized compounds against two gram-positive and two gram-negative bacteria such as Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and two fungi of Candida albicans and Aspergillus niger were investigated by well diffusion method. SEM technique was used to monitor the morphological changes of the bacteria treated with the compounds. The 2,2-Diphenyl-1-picrylhydrazyl(DPPH) and the ferric reducing antioxidant power (FRAP) methods were used to evaluate the antioxidant ability of the ligand and its cadmium(II) complexes. In final, the cytotoxicity properties of the ligand and some cadmium(II) complexes against PC3 cancer cells were evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) bioassay and nitric oxide (NO) level measurement. The morphological changes of prostate cancer (PC3) cells due to treatment with the ligand and its complexes confirmed their anticancer effectiveness.

Tridentate imidazole-based Schiff base metal complexes: molecular docking, structural and biological studies

A novel Schiff base was synthesized by the condensation of imidazole-2-carboxaldehyde with l-histidine in an equimolar ratio. The prepared Schiff base was characterized by elemental analysis and spectral characterization techniques. It was then complexed with a series of 3-d metal(II) ions like manganese, iron, cobalt, nickel, copper and zinc. The coordination properties, nature of bonding and stability of the complexes were deduced from elemental analysis, IR, UV-vis, ¹H NMR, mass, electronic spectra, magnetic, conductivity and thermogravimetric analysis. IR studies support the tridentate behaviour of Schiff base as well as its coordination to the central metal ion through an azomethine nitrogen, deprotonated carboxylic oxygen and imidazole ring nitrogen atoms of histidine. The electronic spectra and magnetic moment data demonstrate that the complexes have an octahedral geometry, except zinc complex, which has a tetrahedral geometry. In vitro antimicrobial activity of the synthesized compounds has been shown to exhibit excellent antibacterial and antifungal activities. The antibacterial property of the prepared Schiff base was further confirmed by conducting a docking study of target proteins involved in the antibacterial mechanism.Communicated by Ramaswamy H. Sarma.

Spectrochemical Properties and Solvatochromism of Tetradentate Schiff Base Complex with Nickel: Calculations and Experiments

The nickel(II) complex with a tetradentate Schiff base ligand obtained by condensation of 1,3‐propanediamine with salicylaldehyde (H₂salpn) was studied in a variety of solvents at room temperature. The product, that is, the N′,N′′‐propylenebis(salicylaldiminato)nickel(II) ([Ni(salpn)]) complex, is brown in color in the solid state. The properties of the ligand and complex were characterized by elemental analysis, solubility in common solvents, molar conductivities, and ultraviolet (UV) and visible (Vis) spectroscopy. The [Ni(salpn)] complex is easily soluble in common solvents such as chloroform, methanol, ethanol, dimethyl formamide, dimethyl sulfoxide, acetonitrile, dioxane, acetone, 2‐propanol, and toluene—a necessary condition for observing solvatochromism. The molar conductivity values, equal to 0.0 S mol^‐1 cm² in these solvents, point to a typical non‐electrolyte behavior for this complex. Spectroscopic measurements were used to confirm the square‐planar geometry of the species in solution and to determine the coordination properties of the donor atoms and their bonding abilities (CFM/AOM parameters), as well as trichromaticity coordinate calculations. The results obtained show that the interactions of the metal with the donors depend on the polarity of the solvent.

A novel antiamoebic agent against Acanthamoeba sp.--A causative agent for eye keratitis infection

The terbium trinitrate.trihydrate.18-crown ether-6, Tb(NO3)3(OH2)3.(18C6) complex has been characterized by elemental analysis, photoluminescence and single X-ray diffraction. The IC50 values were determined based on MTT assay while light and fluorescence microscopy imaging were employed to evaluate the cellular morphological changes. Alkaline comet assay was performed to analyze the DNA damage. The photoluminescence spectrum of the Tb complex excited at 325 nm displayed seven luminescence peaks corresponding to the (5)D4→(7)F(0, 1, 2, 3, 4, 5, 6) transitions. The cytotoxicity and genotoxicity studies indicated that the Tb(NO3)3(OH2)3.(18C6) complex and its salt form as well as the 18C6 molecule have excellent anti-amoebic activity with very low IC50 values are 7, 2.6 and 1.2 μg/mL, respectively, with significant decrease (p<0.05) in Acanthamoeba viability when the concentration was increased from 0 to 30 μg/mL. The mode of cell death in Acanthamoeba cells following treatment with the Tb complex was apoptosis. This is in contrast to the Tb(NO3)3.6H2O salt- and 18C6 molecule-treated Acanthamoeba, which exhibited necrotic type cells. The percentage of DNA damage following treatment with all the compounds at the IC25 values showed high percentage of type 1 with the % nuclei damage are 14.15±2.4; 46.00±4.2; 36.36±2.4; 45.16±0.6%, respectively for untreated, treated with Tb complex, Tb salt and 18C6 molecule. The work features promising potential of Tb(NO3)3(OH2)3.(18C6) complex as anti-amoebic agent, representing a therapeutic option for Acanthamoeba keratitis infection.

Structure investigation of three hydrazones Schiff's bases by spectroscopic, thermal and molecular orbital calculations and their biological activities

Three Schiff's bases AI (2(1-hydrazonoethyl)phenol), AII (2, 4-dibromo 6-(hydrazonomethyl)phenol) and AIII (2(hydrazonomethyl)phenol) were prepared as new hydrazone compounds via condensation reactions with molar ratio (1:1) of reactants. Firstly by reaction of 2-hydroxy acetophenone solution and hydrazine hydrate; it gives AI. Secondly condensation between 3,5-dibromo-salicylaldehyde and hydrazine hydrate gives AII. Thirdly condensation between salicylaldehyde and hydrazine hydrate gives AIII. The structures of AI-AIII were characterized by elemental analysis (EA), mass (MS), FT-IR and (1)H NMR spectra, and thermal analyses (TG, DTG, and DTA). The activation thermodynamic parameters, such as, ΔE(∗), ΔH(∗), ΔS(∗) and ΔG(∗) were calculated from the TG curves using Coats-Redfern method. It is important to investigate their molecular structures to know the active groups and weak bond responsible for their biological activities. Consequently in the present work, the obtained thermal (TA) and mass (MS) practical results are confirmed by semi-empirical MO-calculations (MOCS) using PM3 procedure. Their biological activities have been tested in vitro against Escherichia coli, Proteus vulgaris, Bacillissubtilies and Staphylococcus aurous bacteria in order to assess their anti-microbial potential.

Preparation and structure investigation of novel Schiff bases using spectroscopic, thermal analyses and molecular orbital calculations and studying their biological activities

Two novel Schiff's bases (EB1 and L1) as new macrocyclic compounds were prepared via condensation reactions between bisaldehyde (2,2'-(ethane-1,2-diylbis(oxy))dibenzaldehyde): firstly with hydrazine carbothioamide to give (EB1), secondly with 4,6-diaminopyrimidine-2-thiol to give (L1). EB1 has a general formula C₁₈H₂₀N₆O₂S₂ of mole mass=416.520, and IUPAC name ((N,N'Z,N,N'E)-N,N'-(((ethane1,2diylbis(oxy))bis(2,1phenylene))bis(methanylylidene))bis(1hydrazinylmethanethioamide). L1 has a general formula C₂₀H₁₆N₄O₂S of mole mass=376.10; and IUPAC name 1,2-bis(2-vinylphenoxy)ethane4,6-diaminopyrimidine-2-thiol). The structures of the compounds obtained were characterized based on elemental analysis, FT-IR and (1)H NMR spectra, mass, and thermogravimetric analysis (TG, DTG). The activation thermodynamic parameters, such as, ΔE(*), ΔH(*), ΔS(*) and ΔG(*) were calculated from the TG curves using Coats-Redfern method. It is important to investigate their structures to know the active groups and weak bond responsible for their biological activities. The obtained thermal (TA) and mass (MS) practical results are confirmed by semi-empirical MO-calculation using PM3 procedure, on the neutral and positively charged forms of these novel Schiff bases. Therefore, comparison between MS and TA helps in selection of the proper pathway representing the decomposition of these compounds to give indication about their structures and consequently their biological activities. Their biological activities have been tested in vitro against Escherichia coli, Proteus vulgaris, Bacillissubtilies and Staphylococcus aurous bacteria in order to assess their antimicrobial potential.

Spectroscopic and density functional theory investigation of novel Schiff base complexes

Novel Schiff base (H(2)L, 1,2-bis[(2-(2-mercaptophenylimino)methyl)phenoxy] ethane) derived from condensation of bisaldehyde and 2-aminothiophenol was prepared in a molar ratio 1:2. The ligand and its metal complexes are fully characterized with analytical and spectroscopic techniques. The metal complexes with Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Th(IV) have been prepared and characterized by elemental analyses, IR and (1)H-NMR spectroscopy, thermal and magnetic measurements. The results suggested that the Schiff base is a bivalent anion with hexadentate OONNSS donors derived from the etheric oxygen (O, O'), azomethine nitrogen (N, N') and thiophenolic sulphur (S, S'). The formulae of the complexes were found to be [ML]·xH(2)O (M=Mn(II) (x=0), Co(II) (x=1), Ni(II), (x=1), Cu(II) (x=2) and Zn(II) (x=0)) and [ML]·nCl (M=Cr(III) (n=1), Fe(III) (n=1) and Th(IV) (n=2)). The thermogravimetric analysis of the complexes shows metal oxide remaining as the final product at 700-1000 °C. Density functional theory at the B3LYP/6-31G(*) level of theory was used to investigate molecular geometry, Mulliken atomic charges and energetics. The synclinal-conformer was found to be responsible for complex formation. The calculation showed that ligand has weak field. Structural deformation and the dihedral angles rotation during complexation were investigated. The binding energy of each complex was calculated. The calculated results are in good agreement with experimental data.