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 and genotoxicity of Schiff base transition metal complexes

A new ONNO‐type azomethine ligand, 2,2′‐(ethane‐1,2‐diylidenedinitrilo)dibenzoic acid, (YLH₂) ( 1 ) has been prepared by the condensation of 2‐aminobenzoic acid and glyoxal. The coordination compounds [Ni(YL)] ( 2 ), [Co(YL)] ( 3 ), [Cu(YL)(H₂O)] ( 4 ), [Zn(YL)] ( 5 ), and [Cd(YL)] ( 6 ) of the YLH₂ ligand with five transition metal ions, Ni(II) Co(II), Cu(II), Zn(II), and Cd(II) have been prepared. The structures of these new azomethine compounds are proposed on the basis of the elemental analyses, proton nuclear magnetic resonance, infrared, ultraviolet–visible spectroscopy, and X‐ray powder diffraction patterns. Elemental analyses indicate a ligand metal ratio of 1:1 in the coordination compounds. X‐ray powder diffraction parameters for [Cu(YL)(H₂O)] and [Cd(YL)] compounds correspond to orthorhombic and monoclinic structures, respectively. The ligand acts as a tetradentate ligand bending through oxygen atoms of the hydroxyl groups of benzoic acid and nitrogen atoms of the azomethine groups. In addition, the ligand and its metal complexes have been studied for their possible genotoxic potential. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:119–130, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20665     

Synthesis and physico-chemical studies on transition metal complexes of symmetric bis-Schiff base ligands

Transition Metal Chemistry - A new series of symmetric bis-Schiff bases derived from 1,2-diaminoethane with bis-salicylaldehyde (H2L1) and/or bis-o-hydroxyacetophenone (H2L2) have been prepared....     

Synthesis, spectroscopic characterization and biological activity of the metal complexes of the Schiff base derived from phenylaminoacetohydrazide and dibenzoylmethane

A new series of mono and binuclear Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), La(III), Ru(III), Hf(IV), ZrO(II) and UO(2)(II) complexes of phenylaminodibenzoylhydrazone have been synthesized and characterized by elementals analyses, IR UV-vis spectra, magnetic moments, conductances, thermal analyses (DTA and TGA) and electron spin resonance (ESR) measurements. The IR spectral data show that, the ligand behaves as a neutral bidentate type (15 and 16), monobasic bidentate type (6), or monobasic tridentate type (5, 7, 8, 10, 11, 13, 14, 17-21) or dibasic tridentate type 2-4, 9 and 12 towards the metal ion. Molar conductances in DMF solution indicate that, the complexes are non-electrolytes. The ESR spectra of solid complexes (9 and 10) show axial and non-axial types indicating a [Formula: see text] ground state with significant covalent bond character. However, complexes (11 and 12), show isotropic type, indicating manganese(II) octahedral geometry. Antibacterial and antifungal tests of the ligand and its metal complexes are also carried out and it has been observed that the complexes are more potent bactericides and fungicides than the ligand.     

Synthesis and characterization of some new Schiff base polymers

Seven Schiff base polymers poly 5,5^′-methylenebis(2-hydroxyacetophenone)semicarbazone (PHASC), poly-5,5^′-methylenebis(2-hydroxyacetophenone)thiosemicarbazone (PHATS), poly 6,6^′-methylenebis(2-hydroxynaphthaldehyde)1,2-propylenediimine (PHNPn), poly 6,6^′-methylenebis (2-hydroxynaphthaldehyde)1,3-propylenediimine (PHNPR), poly 6,6^′-methylenebis (2-hydroxy-naphthaldehyde)thiosemicarbazone (PHNTS), poly 6,6^′-methylenebis(2-hydroxy-naphthaldehyde)urea (PHNU) and poly-6,6^′-methylenebis(2-hydroxynaphthaldehyde)semicarbazone (PHNSC) were prepared by polycondensation of 5,5^′-methylenebis(2-hydroxyacetophenone) (MHA) or 6,6^′-methylenebis(2-hydroxynaphthaldehyde) (MHN) with semicarbazide, thiosemicarbazide, 1,2-propylenediamine, 1,3-propylenediamine or urea. The polymers were characterized by elemental micro-analysis, infrared and ultraviolet spectroscopy and viscosity measurements. The reduced viscosity of the polymers measured in dimethylformamide (DMF) was observed in the range 0.32-0.63 dl/g.     

Synthesis, DNA interaction and antibacterial activities of La(III) and Gd(III) complexes of Schiff base derived from o-vanillin and lysine

Two novel complexes, [La(HL)(H₂O)₂NO₃] · NO₃ · H₂O and [Gd(HL)(H₂O)₂NO₃] · NO₃ · H₂O, where HL is a Schiff base derived from o-vanillin and lysine, have been synthesized and characterized by elemental analysis, conductivity measurements, IR, ¹H NMR and thermogravimetric analyses (TGA). The Schiff base ligand behaves as a tetradentate, coordinating through azomethine nitrogen, phenolic oxygen and two carboxylic oxygen atoms. The interaction of these complexes with calf thymus DNA (CT-DNA) was also investigated by spectrometric titration and viscometric measurements. The faint hypochromism of the complexes in the absorption spectra, the remarkable reduction of fluorescence intensity of ethidium bromide (EB) bound DNA, together with a small decrease in the viscosity of the DNA suggest that a partial intercalation may be the preferred binding mode between these two complexes and DNA. The antibacterial activity testing revealed that the complexes and their precursor Schiff base show a weak to moderate activity against Bacillus subtilis, Staphylococcus aureus and Escherichia coli.      

Synthesis,characterization, antifungal,antibacterial and DNA cleavage studies of some heterocyclic Schiff base metal complexes

Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived from indole-3-carboxaldehyde and m-aminobenzoic acid were synthesized and characterized by elemental analysis, molar conductance, IR, UV–Vis, magnetic moment, powder XRD and SEM. The IR results demonstrate the bidentate binding mode of the ligand involving azomethine nitrogen and carboxylato oxygen atoms. The electronic spectral and magnetic moment results indicate that Co(II) and Ni(II) complexes have tetrahedral geometry, while Cu(II) complex is square planar. Powder XRD and SEM indicate the crystalline state and surface morphology studies of the complexes. The antimicrobial activity of the synthesized ligand and its complexes were screened by disc diffusion method. The results show that the metal complexes were found to be more active than the ligand. The nuclease activity of the ligand and its complexes were assayed on CT DNA using gel electrophoresis in the presence of H₂O₂. The Cu(II) complex showed increased nuclease activity in the presence of an oxidant when compared to the ligand and other complexes.     

Synthesis,characterization and thermal study of some tetradentate Schiff base transition metal complexes

Several mononuclear Co(II), Ni(II), Cu(II), and Fe(II) complexes of tetradentate salpren-type diimine, obtained from 3,5-di-tert-butyl-2-hydroxybenzaldehyde and 1,3-diaminopropane have been prepared and characterized by analytical, spectroscopic (FT-IR, UV–VIS) techniques, magnetic susceptibility measurements and thermogravimetric analyses (TG). The thermodynamic and thermal properties of complexes have been investigated. For further characterization Direct Insertion Probe-Mass Spectrometry (DIP-MS) was used and the fragmentation pattern and also stability of the ions were evaluated. The characterization of the end products of the decomposition was achieved by X-ray diffraction. The thermal stabilities of metal complexes of N,N′-bis(3,5-di-t-butylsalicylidene)-1,3-propanediamine ligand (L) were found as Ni(II) > Cu(II) > Co(II) > Fe(II).     

Transition metal complexes of a Schiff base: synthesis,characterization, and antibacterial studies

Synthesis of a new Schiff base derived from 2-hydroxy-5-methylacetophenone and glycine and its coordination with compounds Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and UO₂(VI) are described. The ligand and complexes have been characterized on the basis of analytical, electrical conductance, infrared, ESR and electronic spectra, magnetic susceptibility measurements, and thermogravimetric analysis. The ligand is a dibasic tridentate (ONO) donor in all the complexes except Zn(II), where it is a monobasic bidentate (OO) donor. The solid state DC electrical conductivity of ligand and its complexes have been measured over 313–398 K, and the complexes were semiconducting. Antibacterial activities of ligand and its metal complexes have been determined by screening the compounds against various Gram (+) and Gram (?) bacterial strains.     

New homodi-and heterotrinuclear metal complexes of Schiff base compartmental ligand: interaction studies of copper complexes with calf thymus DNA

The new homodinuclear complexes 1–4 of the type [LM^II ₂Cl₂], heterotrinuclear complexes 5 and 6 of the type [LM^II ₂Sn^IVCl₆] where M = Cu^II, Mn^II, Co^II, Ni^II and Cu^II and Ni^II, respectively have been synthesized and characterized by elemental analysis and various spectroscopic techniques. The homodinuclear complexes possess two different environments (N₂ and N₂O₂donor sets) for holding the metal ions. The metal ion in N₂ set exhibits square planar geometry with two chloride ions in the inner sphere but rhombic structure is found in tetradentate N₂O₂ Schiff base cavity while in heterotrinuclear complexes Sn^IV atom is in the octahedral environment. The interaction of complexes 1 and 5 with calf thymus DNA was carried out by absorption spectroscopy and cyclic voltammetry. The intrinsic binding constants (K _b ) of complex 1 and 5 were determined as 3.2 × 10³ M⁻¹ and 9.6 × 10³ M⁻¹, respectively suggesting that complex 5 binds more strongly to CT-DNA than complex 1. Fluorescence studies along with viscosity measurements have also been checked to authenticate the binding of metal complexes with DNA.     

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 and structure of a Schiff base and its bivalent transition metal complexes

A Schiff base (HCSmz) was synthesized via (E)-cinnamaldehyde with S-methyl dithiocarbazate and six bivalent transition metal complexes [M(CSmz)₂] (M=Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, and Hg²⁺) were prepared. The complexes were characterized by elemental analyses, IR, ¹H NMR, and UV-Vis spectra, and the Ni(II) and Zn(II) complexes were also characterized by single crystal X-ray diffraction. After tautomerism of thiotone to thioenol and deprotonization of the thioenol, two ligands chelate the metal by two nitrogens of azomethine and two sulfurs of thioenol. Ni(CSmz)₂ crystallizes in the centrosymmetric space group P2₁ /n with a perfectly square planar trans-configuration with Ni located at the center of the square; crystal packing is stabilized by intra- and intermolecular C–H···S hydrogen bonds. Zn(CSmz)₂ is in the mirror-symmetric space group I4₁ /a in a distorted tetrahedral geometry with two equivalent Zn–N and Zn–S bonds; crystal packing is stabilized by intermolecular C–H···π hydrogen bonds.     

Quinoxaline-based Schiff base transition metal complexes: review

The literature survey highlights spectra and biological activity of transition metal complexes derived from Schiff bases of quinoxaline. The extensive studies of synthesis, spectral, structural characterization, and biological activities of the metal complexes with heterocyclic Schiff bases of quinoxaline are reviewed.     

Synthesis and physicochemical studies of metal complexes of ferrocene Schiff base derivatives

Two new Schiff bases were prepared by condensing acetylferrocene and 1,1′-diacetylferrocene with S-methyl- dithiocarbazate. Complexes of the two ligands acetylferrocene-1-hydrazono-S-methyldithiocarbazate HmaL and diacetylferrocene-1,1′-dihydrazono-S-methyldithio-carbazate H2daL, with copper(II), nickel(II) and cobalt(II) ions were isolated. The ligands coordinate to the metal ions through either their thioketone or thioenol forms. Both mono- and bis-ligand metal complexes as well as bis-metal complexes of the general formulae: [(H2daL)M]2+, [(daL)M], [(HmaL)2M]2+, [(maL)2M], [(HmaL)2MX2], [(H2daL)M2X4] and [(daL)M2X2] were prepared. All compounds under investigation were characterized and some of their physicochemical properties are reported. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis, structural, thermal studies and biological activity of a tridentate Schiff base ligand and their transition metal complexes

Schiff base (L) ligand is prepared via condensation of pyridine-2,6-dicarboxaldehyde with -2-aminopyridine. The ligand and its metal complexes are characterized based on elemental analysis, mass, IR, solid reflectance, magnetic moment, molar conductance, and thermal analyses (TG, DTG and DTA). The molar conductance reveals that all the metal chelates are non-electrolytes. IR spectra shows that L ligand behaves as neutral tridentate ligand and bind to the metal ions via the two azomethine N and pyridine N. From the magnetic and solid reflectance spectra, it is found that the geometrical structures of these complexes are octahedral (Cr(III), Fe(III), Co(II), Ni(II), Cu(II), and Th(IV)) and tetrahedral (Mn(II), Cd(II), Zn(II), and UO2(II)). The thermal behaviour of these chelates shows that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The activation thermodynamic parameters, such as, E*, ΔH*, ΔS* and ΔG* are calculated from the DTG curves using Coats-Redfern method. The synthesized ligand, in comparison to their metal complexes also was screened for its antibacterial activity against bacterial species, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus pyogones and Fungi (Candida). The activity data shows that the metal complexes to be more potent/antibacterial than the parent Schiff base ligand against one or more bacterial species.     

Derivatives of phosphate Schiff base transition metal complexes: synthesis, studies and biological activity

We report the synthesis and structural characterization of series of tetra- and hexacoordinate metal chelate complexes of phosphate Schiff base ligands having the general composition LMX(n).H(2)O and L(2)MX(n) (L=phosphate Schiff base ligand; M=Ag(+), Mn(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), or Fe(3+) and X=NO(3)(-), Br(-) or Cl(-)). The structure of the prepared compounds was investigated using elemental analysis, IR, 1H and 31P NMR, UV-vis, mass spectra, solid reflectance, magnetic susceptibility and conductance measurements as well as conductometric titration. In all the complexes studied, the ligands act as a chelate ligand with coordination involving the phosphate-O-atom and the azomethine-N-atom. IR, solid reflectance spectra and magnetic moment measurement are used to infer the structure and to illustrate the coordination capacity of ligand. IR spectra show the presence of coordinated nitrate and water molecule, the magnetic moments of all complexes show normal magnetic behavior and the electronic spectra of the metal complexes indicate a tetra- and octahedral structure for Mn(2+), octahedral structure of Fe(3+) and both square-planar and distorted octahedral structure for Cu(2+) complexes. Antimicrobial activity of the ligands and their complexes were tested using the disc diffusion method and the chosen strains include Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Microsporum canis, Trichophyton mentagrophyte and Trichophyton rubrum. Some known antibiotics are included for the sake of comparison and the chosen antibiotic are Amikacin, Doxycllin, Augmantin, Sulperazon, Unasyn, Septrin, Cefobid, Ampicillin, Nitrofurantion, Traivid and Erythromycin.     

Synthesis,crystal structures,spectroscopic studies and antibacterial properties of a series of mononuclear cobalt(III) Schiff base complexes

New complexes of cobalt(III) with the tridentate and tetradentate Schiff base ligands: 3-methoxy-2-{(Z)[(2-hydroxyphenyl)imino]methyl}phenol (H₂L¹), 4-[(2-hydroxyphenyl)imino]-2-pentanone (H₂L²); and 2-((E)-1-(2-((E)-1-(2-hydroxy-4,5-dimethylphenyl)ethylideneamino)ethylimino)ethyl)-4,5 dimethylphenol (H₂L³), namely [Co^III(L¹)(N-MeIm)₃]PF₆ (1), [Co^III(L¹)(py)₃]ClO₄ (2), [Co(L¹)(py)₃][Co(L¹)₂] (3) and [Co^III(L²)(N-MeIm)₃]PF₆ (4) and [Co(L³)(N-MeIm)₂]PF₆ (5), were synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of the complexes were determined by X-ray crystallography. In each of these complexes, the cobalt(III) centre has a slightly distorted octahedral environment, utilizing all available coordination centres of the ligands. The complexes were also screened for in vitro antibacterial activities against four human pathogenic bacteria, and their minimum inhibitory concentrations indicated good antibacterial activities.     

Synthesis,spectral characterization,antioxidant, anticancer in vitro,and DNA cleavage studies of a series of ruthenium(II) complexes bearing Schiff base ligands

Ruthenium(II) complexes with 2-acetylpyridine-thiosemicarbazones (L¹–L⁴) were synthesized and characterized by analytical and spectral (FT-IR, UV–vis, NMR [¹H, ¹³C and ³¹P], and ESI-Mass) methods. Systematic biological investigations, free radical scavenging, anticancer activities, and DNA cleavage studies, were carried out for the complexes. Antioxidant studies showed that the complexes have significant antioxidant activity against DPPH, hydroxyl, nitric oxide radicals and hydrogen peroxide assay. The in vitro cytotoxicity of complexes against breast cancer (MCF-7) cell line was assayed showing high cytotoxicity with low IC₅₀ values indicating their efficiency in destroying the cancer cells even at very low concentrations. The DNA cleavage studies showed that the complexes efficiently cleaved DNA.     

Synthesis, structure, and catalytic oxidation chemistry from the first oxo-imido Schiff base metal complexes

The molybdenum oxo-imido complex, [Mo(O)(NtBu)Cl2(dme)] (1), was obtained from the reaction between [MoO2Cl2(dme)] and [Mo(NtBu)2Cl2(dme)]. Reactions between [Mo(O)(NR)Cl2(dme)] (where R = tBu or 2,6-iPr2C6H3) and the disodium Schiff base compounds Na(2)(3,5-tBu2)2salen, Na(2)(3,5-tBu2)2salpen, and Na(2)(7-Me)2salen afforded the first oxo-imido transition metal Schiff base complexes: [Mo(O)(NtBu)[(3,5-tBu2)2salen]] (2), [Mo(O)(NtBu)[(3,5-tBu2)2salpen]] (3), and [Mo(O)(N-2,6-iPr2C6H3)[(7-Me)2salen]] (4), respectively. The compounds [Mo(NtBu)2[(3,5-tBu2)2salpen]] (5) from [Mo(NtBu)2(NHtBu)2] and [Mo(N-2,6-iPr2C6H3)(2)[(7-Me)2salen]](6) from [Mo(N-2,6-iPr2C6H3)(2)(NHtBu)2] (7) are also reported. Compounds 1-7 were characterized by NMR, IR, and FAB mass spectroscopy while compounds 3, 4, and 5 were additionally characterized by X-ray crystallography. In conjunction with tBuOOH as oxidant, compound 3 is a catalyst for the oxidation of benzyl alcohol to benzaldehyde and cis-cyclooctene and 1-octene to the corresponding epoxides.     

Antimicrobial and anticancer activities of Schiff base ligand and its transition metal mixed ligand complexes with heterocyclic base

A new Schiff base ligand (HL) was prepared via a condensation reaction of quinoline‐2‐carboxaldhyde with 2‐aminophenol in a molar ratio of 1:1. Its transition metal mixed ligand complexes with 1,10‐phenanthroline (1,10‐phen) as co‐ligand were also synthesized in a 1:1:1 ratio. HL and its mixed ligand complexes were characterized using elemental analysis, infrared, ¹H NMR, mass and UV–visible spectroscopies, molar conductance, magnetic measurements, solid reflectance, thermal analysis, electron spin resonance and X‐ray diffraction. Molar conductance measurements showed that all complexes have an electrolytic nature, except Cd(II) complex. From elemental and spectral data, the formulae [M(L)(1,10‐phen)(H₂O)]Cl_x?nH₂O (where M = Cr(III) (x = n = 2), Mn(II) and Ni(II) (x = 1, n = 2), Fe(III) (x = n = 2), Co(II), Cu(II) and Zn(II) (x = 1, n = 2)) and [Cd(L)(1,10‐phen)Cl]?3H₂O for the metal complexes have been proposed. The geometric structures of complexes were found to be octahedral. Powder X‐ray diffraction reflected the crystalline nature of the complexes; however, the Schiff base is amorphous. HL and its mixed ligand complexes were screened against Gram‐positive bacteria (Streptococcus pneumoniae and Bacillus subtilis) and Gram‐negative bacteria (Pseudomonas aeruginosa and Escherichia coli). Antifungal activity was determined against Aspergillus fumigatus and Candida albicans, the data showing that most complexes had activity less than that of the Schiff base while Mn(II), Fe(III) and Ni(II) complexes showed no significant antifungal activity. The anticancer activity of HL and its metal complexes was also studied against breast and colon cell lines. The metal complexes showed IC₅₀ higher than that of HL, especially the Cu(II) complex which showed the highest IC₅₀ against breast cell line.