Synthesis,characterization, thermal,and antimicrobial studies of binuclear metal complexes of sulfa-guanidine Schiff bases

A series of metal complexes of Schiff bases derived from condensation of sulfa-guanidine with 1-benzoylacetone (H₂L¹), 2-hydroxybenzophenol (H₂L²), dibenzoylmethane (H₂L³), 5-methylisatine (H₂L⁴), and 1-methylisatine (H₂L⁵) have been synthesized. The complexes are characterized by elemental analysis, molar conductance, magnetic moment measurements, IR, UV–Vis, ¹H NMR, and ESR spectra, as well as thermogravimetric analysis. The low molar conductance values indicate the complexes are nonelectrolytes. IR and ¹H NMR spectra show that H₂L¹–H₂L⁵ are coordinated to metal ions by two bidentate centers. Mn(II), Co(II), Ni(II), and Cu(II) complexes display paramagnetic behavior, whereas the Zn(II)-complex was diamagnetic. All studies confirm the formation of an octahedral geometry for [Cu₂L¹(AcO)₂(H₂O)₆] · 3H₂O (1), [Mn₂L⁴(AcO)₂(H₂O)₆] · 2H₂O (6), [Ni₂L⁴(AcO)₂(H₂O)₆] · 2H₂O (8), a tetrahedral geometry for [Cu₂L²(AcO)₂(H₂O)₂] (2), [Cu₂(L⁴)₂] (4), [Co₂(L⁴)₂] · 2H₂O (7) and [ZnHL⁴(AcO)(H₂O)] · 2H₂O (9) and a trigonal bipyramid geometry for [Cu₂L³(AcO)₂(H₂O)₄] (3) and [Cu₂HL⁵(AcO)₃(H₂O)₃] · H₂O (5). H₂L⁴ was most effective on Gram negative, Gram positive bacteria, and fungi (diameters inhibition zone ranged between 10.5–27.5 mm) after 24 and 48 h, respectively. Complex 8 showed moderate antimicrobial activity. Its minimum inhibitory concentration (MIC) against Escherichia coli, Bacillus subtilis, Candida albicans and Aspargllus flavas was 20 mg L^–1. The compound proved to be of moderate toxicity and its LD₅₀ was 20 mg L^–1.     

Synthesis, potentiometric and antimicrobial activity studies on DL-amino acids-Schiff bases and their complexes

A relationship between antimicrobial activities and the formation constants of amino acid-Schiff bases and their Cu(II) and Ni(II) complexes was studied. For this purpose, a series of Schiff bases were prepared from DL-amino acids (DL-glycine, DL-alanine) and halo aldehydes (5-chloro-2-hydroxybenzaldehyde, 5-bromo-2-hydroxybenzaldehyde). Schiff bases and their Cu(II) and Ni(II) complexes were characterized by the elemental analysis, spectral analysis, magnetic moment (at ca. 25°C), molar conductivity, and thermal analysis data. The complexes were found to have general compositions [ML(H₂O)]. The protonation constants of the Schiff bases and stability constants of the complexes were determined potentiometrically in a dioxane-water (1: 1) solution at 25°C and 0.1 M KCl ionic strength. Antimicrobial activities of the Schiff bases and their complexes were estimated for six bacteria, such as Bacillus cereus RSKK 863, Staphylococcus aureus ATCC 259231, Micrococcus luteus NRLL B-4375, Escherichia coli ATCC 11230, Aeromonas hydrophila 106, Pseudomonas aeroginosa ATCC 29212, and the yeast Candida albicans ATCC 10239. The role of halogen substitution on the ligands, effect of the metal ion, and stabilities of the complexes are discussed on antimicrobial activities. The text was submitted by the authors in English.     

Synthetic,spectral, structural and antimicrobial studies of some Schiff bases 3-d metal complexes

The complexes of tailor made ligands with life essential metal ions may be an emerging area to answer the problems of multi-drug resistance (MDR). The coordination complexes of VO(II), Co(II), Ni(II) and Cu(II) with the Schiff bases derived from 3-bromobenzaldehyde/3-chlorobenzaldehyde with 2-aminophenol have been synthesized and characterized by elemental analysis, molar conductance, electronic spectra, FT-IR, ESR, FAB mass, thermal and magnetic susceptibility measurements, FAB mass and thermal data show degradation of complexes. Both the ligands behave as bidentate coordinating through O and N donor. The complexes exhibit coordination number 4, 5 or 6. X-ray powder diffraction data shows that four (2, 3, 6 and 7) complexes are crystallized in tetragonal system. The in vitro biological screening effects of the investigated compounds were tested against the bacteria Escherichia coli, Staphylococcus aureus and Streptococcus fecalis and the fungi Aspergillus niger, Trichoderma polysporum and Candida albicans by serial dilution method. A comparative study of the MIC values of the Schiff base and their Co(II) (6) and Cu(II) (8) complexes, indicates that the metal complexes exhibit higher or lower antimicrobial activity than the free ligand (L₂).     

Synthesis,spectral, thermal,potentiometric and antimicrobial studies of transition metal complexes of tridentate ligand

A series of metal complexes of Cu(II), Ni(II), Co(II), Fe(III) and Mn(II) have been synthesized with newly synthesized biologically active tridentate ligand. The ligand was synthesized by condensation of dehydroacetic acid (3-acetyl-6-methyl-(2H) pyran-2,4(3H)-dione or DHA), o-phenylene diamine and fluoro benzaldehyde and characterized by elemental analysis, molar conductivity, magnetic susceptibility, thermal analysis, X-ray diffraction, IR, ¹H-NMR, UV–Vis spectroscopy and mass spectra. From the analytical data, the stoichiometry of the complexes was found to be 1:2 (metal:ligand) with octahedral geometry. The molar conductance values suggest the non-electrolyte nature of metal complexes. The IR spectral data suggest that the ligand behaves as a dibasic tridentate ligand with ONN donor atoms sequence towards central metal ion. Thermal behaviour (TG/DTA) and kinetic parameters calculated by the Coats–Redfern and Horowitz–Metzger method suggest more ordered activated state in complex formation. To investigate the relationship between stability constants of metal complexes and antimicrobial activity, the dissociation constants of Schiff bases and stability constants of their binary metal complexes have been determined potentiometrically in THF–water (60:40%) solution at 25 ± 1 °C and at 0.1 M NaClO₄ ionic strength. The potentiometric study suggests 1:1 and 1:2 complexation. Antibacterial and antifungal activities in vitro were performed against Staphylococcus aureus, Escherichia coli and Aspergillus niger, Trichoderma, respectively. The stability constants of the metal complexes were calculated by the Irving–Rosotti method. A relation between the stability constant and antimicrobial activity of complexes has been discussed. It is observed that the activity enhances upon complexation and the order of antifungal activity is in accordance with stability order of metal ions.     

Spectroscopic studies of metal complexes with redox-active hydrogenated Schiff bases

Synthesis and spectroscopic (IR, UV-visible, ESR) characterization of metal(II) complexes M(Lx')2, (where M = Co(II), NI(II), VO(II), Pd(II), Lx' = L1', L2', L3' are monoanion of unsubstituted, 5-Cl and 5-Br substituted-2-hydroxybenzylamine) with redox-active N-(3,5-ditert-butyl-4-hydroxyphenyl)-2-hydroxybenzylamine ligands as well as radical species generated from these compounds by the oxidation with PbO2 are reported. ESR studies indicate that the VO(Lx')2 and Ni(Lx')2 complexes, in opposite to their salicylaldimine precursors, are more readily oxidized with lead dioxide and results in the formation of the indophenoxyl type stable radical. The formed radical species are very similar to each other and quite different from those of the salicylaldimine analogous according to their g-factors and hyperfine coupling constants. The nine line radical spectra observed in the oxidation of Co(Lx')2, on standing under vacuum, gradually converted to the signals characteristic of the low-spin Co(II) (g(x,y) = 2.276, g(z) = 1.998, A(xy)Co = 122.7 G, A(z)Co = 150 G) and radical containing Co(III) intermediate with g(x,y) = 2.015, A(xy)Co = 4.66 G, g(z) = 1.989, A(z)Co = 10 G were also observed.     

Synthesis and antioxidant, antimicrobial evaluation, DFT studies of novel metal complexes derivate from Schiff base

In Iraq, like most developing countries, attempts are being made to synthesize new compounds with several pharmacological properties. (E)-2-(3-(2-imino-1-methylimidazolidin-4-ylidene)-1-methylguanidino)acetic acid (L) has been synthesized and used as a ligand for the formation of Cr(III), Co(II), Ni(II), and Cu(II) complexes. The chemical structures of synthesized compounds were characterized using different spectroscopic methods. All chelates except Ni(II) chelate are found to be octahedral structures, Ni(II) chelate was square planar. The stability for the prepared complexes was studied theoretically using density function theory. The total energy for the complexes was calculated and it was shown that the copper complex is the most stable one. Ligand and complexes were tested against selected types of microbial organisms and showed significant activities. The free-radical scavenging activity of ligand and metal complexes have been determined by their interaction with the stable free-radical DPPH and all the compounds have shown encouraging antioxidant activities.     

Synthesis,crystal structure,spectroscopic, and biological studies on Cu(II) complexes of N,O donor dimethyl isoxazole Schiff bases

Cu(II) complexes with Schiff bases DMIIMP, DMIIMBD, DMIIMBP, DMIIMCP, DMIIMMP, and DMIIMNP (see Introduction for definitions) are derived from condensation of 3,4-dimethyl 5-amino-isoxazole with salicylaldehyde and substituted salicylaldehydes. The newly synthesized ligands were characterized by IR, UV-Vis, ¹H NMR, ¹³C NMR, mass spectra, and elemental analysis. The Cu(II) complexes were characterized by IR, UV-Vis, ESR, elemental analysis, magnetic moments, thermogram, DTA, and single crystal analysis. The complexes have general formula [M(L)₂]. The Schiff bases are bidentate coordinating through the azomethine nitrogen and phenolic oxygen of salicylaldehydes. Based on the analytical and spectral data, four-coordinate geometry is assigned for all the complexes. ESR and single crystal analysis suggests square planar geometry for all complexes. [Cu(DMIIMP)₂] crystallizes in the orthorhombic system. Antimicrobial studies of Schiff bases and their metal complexes show significant activity with the metal complexes showing more activity than corresponding Schiff bases. Cytotoxicity of the copper complexes on human cervical carcinoma cells (HeLa) was measured using the Methyl Thiazole Tetrazolium assay.     

Synthesis, spectral characterization of Schiff base transition metal complexes: DNA cleavage and antimicrobial activity studies

A new series of transition metal complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), VO(IV), Hg(II) and Cd(II) have been synthesized from the Schiff base (L) derived from 4-aminoantipyrine, 3-hydroxy-4-nitrobenzaldehyde and o-phenylenediamine. Structural features were obtained from their elemental analyses, magnetic susceptibility, molar conductance, mass, IR, UV-Vis, ¹H NMR and ESR spectral studies. The data show that these complexes have composition of ML type. The UV-Vis, magnetic susceptibility and ESR spectral data of the complexes suggest a square-planar geometry around the central metal ion except VO(IV) complex which has square-pyramidal geometry. The redox behaviour of copper and vanadyl complexes was studied by cyclic voltammetry. Antimicrobial screening tests gave good results in the presence of metal ion in the ligand system. The nuclease activity of the above metal complexes shows that Cu, Ni and Co complexes cleave DNA through redox chemistry whereas other complexes are not effective.     

Synthesis,potentiometric and antimicrobial activity studies on 2-pyridinilidene-DL-amino acids and their complexes

To investigate the relationship between antimicrobial activities and the formation constants of Cu^II, Ni^II and Co^II complexes with three Schiff bases, which were obtained by the condensation of 2-pyridinecarboxyaldehyde with DL-alanine, DL-valine and DL-phenylalanine, have been synthesized. Schiff bases and the complexes have been characterized on the basis of elemental analyses, magnetic moments (at ca. 25 °C), molar conductivity, thermal analyses and spectral (i.r., u.v., n.m.r.) studies. The i.r. spectra show that the ligands act in a monovalent bidentate fashion, depending on the metal salt used and the reaction pH = 9, 8 and 7 medium, for Cu^II, Ni^II and Co^II, respectively. Square-planar, tetrahedral and octahedral structures are proposed for Cu^II, Ni^II and Co^II, respectively. The protonation constants of the Schiff bases and stability constants of their ML-type complexes have been calculated potentiometrically in aqueous solution at 25 ± 0.1 °C and at 0.1 M KCl ionic strength. Antimicrobial activities of the Schiff bases and the complexes were evaluated for three bacteria (Bacillus subtillis, Staphylococcus aureus, and Escherichia coli) and a yeast (Candida albicans). The structure–activity correlation in Schiff bases and their metal(II) complexes are discussed, based on the effect of their stability contants.     

Synthesis,DNA binding,and antimicrobial studies of novel metal complexes containing a pyrazolone derivative Schiff base

A novel series of Co(II), Ni(II), Cu(II), Zn(II), and VO(IV) complexes has been synthesized from the Schiff base derived from 4-[(3,4-dimethoxybenzylidene)amino]-1,5-dimethyl-2-phenyl-1,2-dihydropyrazol-3-one and 1,2-diaminobenzene. Structural features were determined by analytical and spectral techniques. Binding of synthesized complexes with calf thymus DNA (CT DNA) was studied by spectroscopic methods and viscosity measurements. Experimental results indicate that the complexes are able to form adducts with DNA and to distort the double helix by changing the base stacking. Lower DNA affinity of the VO(IV) complex is caused by the change of coordination geometry by the vanadyl ion resulting in a somewhat unfavorable configuration for the DNA binding. Oxidative DNA cleavage activities of the complexes were studied with supercoiled (SC) pUC19 DNA using gel electrophoresis; the mechanism studies revealed that the hydroxyl radical is likely to be the reactive species responsible for the cleavage of pUC19 DNA by the synthesized complexes. The in vitro antimicrobial screening effects of the investigated compounds were monitored by the disc diffusion method. The synthesized Schiff base complexes exhibit higher antimicrobial activity than the respective free Schiff base.     

Synthesis,spectral characterization and biological studies of transition metal(II) complexes with triazole Schiff bases

New metal based triazoles (1–12) have been synthesized by the interaction of novel Schiff base ligands (L¹–L³) with the Co(II), Ni(II), Cu(II) and Zn(II) metal ions. The Schiff base ligands and their all metal(II) complexes have been thoroughly characterized using various physical, analytical and spectroscopic techniques. In vitro bacterial and fungal inhibition studies were carried out to examine the antibacterial and antifungal profile of the Schiff bases in comparison to their metal(II) complexes against two Gram‐positive, four Gram‐negative and six fungal strains. The bioactivity data showed the metal(II) complexes to have more potent antibacterial and antifungal activity than their uncomplexed parent Schiff bases against one or more bacterial and fungal species. Copyright © 2012 John Wiley & Sons, Ltd.     

Structures,luminescence, and antibacterial studies of two transition metal complexes involving Schiff bases

Two new transition metal complexes of Schiff bases, [Pd₂(L1)₂Cl₂] (1) and [Zn(L2)₂] (2), [L1?=?N-(4-fluorobenzylidene)-2,6-diisopropylbenzenamine and L2?=?2,4-dibromo-6-((E)(mesitylimino)methyl)phenol], have been synthesized solvothermally and characterized by elemental analysis, IR-spectroscopy, thermogravimetric analysis, powder X-ray diffraction, UV-vis absorption spectra, and single-crystal X-ray diffraction. Complex 1 is a μ-chloro-bridged dinuclear cyclometallated Pd(II) complex, whereas 2 is mononuclear with the Zn^II tetrahedrally coordinated by two L2. Both 1 and 2 display photoluminescence in the solid state at 298?K (fluorescence lifetimes τ?=?22.516?ns at 468?nm for 1, τ?=?3.697?μs at 490?nm for 2). These Schiff bases and their metal compounds have been screened for antibacterial activity against several bacteria, and the results are compared with the activity of penicillin.     

Some divalent metal(II) complexes of salicylaldehyde‐derived Schiff bases: Synthesis,spectroscopic characterization,antimicrobial and in vitro anticancer studies

Mononuclear transition metal(II) complexes of the type M(L)₂?2H₂O (where M = Co, Ni, Cu, Zn) have been synthesized from uninegative Schiff base ligands (HL₁–HL₄) designed by condensation of 4‐fluorobenzylamine with 2‐hydroxy‐1‐naphthaldehyde/3,5‐dichlorosalicylaldehyde/3,5‐dibromosalicylaldehyde/3‐bromo‐5‐chlorosalicylaldehyde. The compounds were successfully characterized using spectroscopic and physiochemical methods together with elemental analysis. Spectroscopic elucidation indicates a monobasic bidentate nature of ligands coordinated via deprotonated phenolic oxygen and azomethine nitrogen atom which suggests an octahedral geometry around the central metal ions. The complexes and ligands were screened for their in vitro antimicrobial activity against bacterial and fungal strains, the zinc(II) complexes being more active against the tested microbial strains. Further, the metal complexes were found to be more active than the uncomplexed ligands due to chelation process and, moreover, the complexes were more active against fungal strains than bacterial strains. Cytotoxic activities of all compounds were evaluated towards human alveolar adenocarcinoma epithelial cell line (A549), human breast adenocarcinoma cell line (MCF7), human prostate cancer cell line (DU145) and one normal human lung cell line (MRC‐5) using MTT colorimetric assay with doxorubicin as a standard. The zinc complexes were most active against the cancer cell lines and also found to be less toxic against MRC‐5 normal cell line than standard doxorubicin.     

Synthesis and spectroscopic studies of new binuclear transition metal complexes of Schiff bases derived from 4,6-diacetylresorcinol

Two new series of copper(II), nickel(II), cobalt(II), zinc(II), iron(III), chromium(III), vanadyl(IV) and uranyl(VI) complexes with two bifunctional tridentate Schiff base, H₄L¹ and H₂L² ligands have been prepared. The Schiff base, H₄L¹ and H₂L², ligands were synthesized by the condensation of 4,6-diacetylresorcinol with o-aminophenol or o-phenylenediamine. The ligands are either di- or tetra-basic with two symmetrical sets of either OON or NNO tridentate chelating sites. The ligands and their metal complexes have been characterized by elemental analysis, ¹H-n.m.r., FT-IR, mass, electronic, esr spectra and thermal gravimetric analysis and magnetic susceptibility. With the exception of Co^II ion with H₂L² which afforded a trinuclear complex, a variety of binuclear complexes for the rest of the metal complexes were obtained with the ligands in its di- or tetra-deprotonated forms. The bonding sites are the azomethine and amino nitrogen atoms, and phenolic oxygen atoms. The metal complexes exhibit different geometrical arrangements such as square planar, tetrahedral, square pyramid and octahedral arrangement.     

Synthesis,spectral and redox properties of metal complexes of macrocyclic tetraaza chiral Schiff bases

New transition metal(II) coordination compounds of tetraaza macrocyclic chiral Schiff bases, derived from 2-hydroxybenzylideneacetylacetone or 4-hydroxybenzylideneacetylacetone and (1R, 2R)-(–)-1,2-diaminocyclohexane, have been prepared and characterised spectroscopically and electrochemically. E.p.r. spectral data for the Cu^II complexes reveal a strong metal-to-ligand -interaction in their square-planar configuration and the broadening of the g component is due to the strain created by 1R and 2R groups in the cyclohexane rings. The cyclic voltammetric (c.v.) data of the copper complexes show an unusual oxidation state of Cu^III, while Co^II complexes show a reversible Co^II/Co^III redox peak along with an additional peak in the negative potential region characteristic of reversibly bound oxygen. The c.v. results reveal that both Cu^II and Co^II complexes bind axially with added bases. The spectroscopic results reveal that copper, cobalt and nickel complexes are in square-planar geometry, whereas manganese is in octahedral geometry.     

Synthesis,characterization and antibacterial properties of Schiff bases and Schiff base metal complexes derived from 2,3-diamino- pyridine

New copper(II), zinc(II) and nickel(II) Schiff base complexes derived from 2,3-diaminopyridine (DAPY) and selected aldehydes, namely salicylaldehyde (SalH), 4-hydroxybenzaldehyde (4-OHBenz) and 4-nitrobenzaldehyde (4-NO₂Benz), and one mixed Schiff base, DAPY-{4-OHBenz}{SalH} were prepared and characterized by a combination of elemental analyses, i.r. and n.m.r. spectra, and magnetic susceptibility measurements. The Schiff bases and some of the metal complexes display antibacterial properties.