Role of Knoevenagel condensate pyrazolone derivative Schiff base ligated transition metal complexes in biological assay and cytotoxic efficacy

A new bioessential Knoevenagel condensate Schiff base ligand (L) was synthesized by the reaction of 3‐(4‐hydroxy‐3‐methoxybenzyl)pentane‐2,4‐dione and 4‐aminoantipyrine. The ligand forms monomeric divalent transition metal complexes ( 1 – 4 ) which were characterized using spectral and analytical data. All these complexes have the general formula [ML]Cl₂, where M = Co(II), Ni(II), Cu(II) and Zn(II). They are electrolytic in nature and adopt square planar geometry. The binding propensity of these complexes with calf thymus DNA was investigated using absorption spectrophotometric titration, cyclic voltammetry and viscosity measurements. The binding constant values imply that the complexes bind with DNA via intercalation mode. The in vitro antibacterial and antifungal activities reveal that the complexes have good antimicrobial efficacy against a set of pathogens. The nucleolytic cleavage activity of these complexes on pUC18 DNA was investigated using agarose gel electrophoresis. Also, the in vitro cytotoxicity of the synthesized complexes against a panel of human tumour cell lines (MCF‐7 and HeLa) and normal cell lines (NHDF and HEK) was assayed using the MTT method. Interestingly, complex 1 exhibits more potent anticancer activity than cisplatin and other complexes.     

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, 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.     

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 and spectroscopic studies of binuclear metal complexes of a tetradentate N2O2 Schiff base ligand derived from 4,6-diacetylresorcinol and benzylamine

A tetradentate N2O2 donor Schiff base ligand, H2L, was synthesized by the condensation of 4,6-diacetylresorcinol with benzylamine. The structure of the ligand was elucidated by elemental analyses, IR, 1H NMR, electronic and mass spectra. Reaction of the Schiff base ligand with nickel(II), cobalt(II), iron(III), cerium(III), vanadyl(IV) and uranyl(VI) ions in 1:2 molar ratio afforded binuclear metal complexes. Also, reaction of the ligand with several copper(II) salts, including Cl-, NO3-, AcO-, ClO4- and SO42- afforded different metal complexes that reflect the non-coordinating or weakly coordinating power of the ClO(4)(-) anion as compared to the strongly coordinating power of SO42- and Cl- anions. Characterization and structure elucidation of the prepared complexes were achieved by elemental and thermal analyses, IR, 1H NMR, electronic, mass and ESR spectra as well as magnetic susceptibility measurements. The metal complexes exhibited different geometrical arrangements such as square planar, octahedral, square pyramidal and pentagonal bipyramidal arrangements. The variety in the geometrical arrangements depends on the nature of both the anion and the metal ion.     

Complexation behavior of Schiff base toward transition metal ions

Complexes of Iron, Cobalt, Nickel and Zinc ions with the Schiff base derived from p-dimethylaminobenzaldehyde and o-aminobenzoic acid were synthesized and investigated by several techniques using elemental analyse (C,H,N), molar conductance measurements, infrared and electronic spectra. The elemental analysis data suggest the stoichiometry to be 1:1 [M:L] ratio formation. The molar conductance measurements reveal the presence of non-electrolytic nature complexes. Infrared spectral data agreed with the coordination to the central metal ions through both the nitrogen atom of the azomethine and oxygen atom of the carboxyl group of the 2-aminobenzoic acid moiety. The electronic spectral data suggest the existence of octahedral geometry for Fe(III) complex, square planar geometry for Co(II) and Ni(II) complexes and tetrahedral geometry for Zn(II) complex.     

Schiff碱二价金属离子配合物的合成及抗菌性

氨基酸、肽、蛋白质、酶等生物大分子中半光氨酸残基上的硫原子与一些过渡金属离子形成的配合物具有特殊的生物活性,因此配体和配合物的研究一直受到人们的重视[1,2]。我们设计并合成出的乙酰基硫代甲酰取代苯胺缩氨基脲Schiff碱具有与这些生物大分子相同的配位原子,可以作为研     

Synthesis,characterization, biological activity,and corrosion inhibition in acid medium of unsymmetrical tetradentate N2O2 Schiff base complexes

Four divalent metal(II) complexes, namely [Co(II)L(H₂O)Cl]·2H₂O, [Ni(II)L(H₂O)Cl]·4H₂O, [Cu(II)L(H₂O)Cl]·3H₂O, and [Zn(II)L(H₂O)Cl]·5H₂O, {L = 2‐furan‐2‐ylmethyleneamino‐phenyl‐iminomethylphenol}, were synthesized and characterized by several techniques. The molar conductance measurement of all analyzed complexes in DMSO showed their non‐electrolytic nature. The new Schiff base ligand (HL) acts as tetradentate ligand, coordinated through deprotonated phenolic oxygen, furan ring oxygen, and two azomethine nitrogen atoms. The ligand field parameters were measured for the metal complexes, which were found to be in the range notified for an octahedral structure. The molecular structural parameters of the synthesized HL ligand and its related metal(II) complexes were calculated and correlated with the experimental parameters such as infrared (IR) data. The investigated ligand and metal complexes were screened for their in vitro antimicrobial activities against different types of fungal and bacterial strains. The resulting data confirmed the examined compounds as a highly promising bactericides and fungicides. The antitumor activities of all inspected compounds were evaluated against colon carcinoma (HCT‐116) and mouse myelogenous leukemia carcinoma (M‐NFS‐60) cell lines. The inhibition effect of HL ligand and its isolated complexes on the corrosion carbon in the form of a rod of area 0.35 cm² in HCl was investigated by measuring the weight loss at 25 °C.     

Synthesis, spectroscopic, antimicrobial, DNA binding and cleavage studies of some metal complexes involving symmetrical bidentate N, N donor Schiff base ligand

The Schiff base ligand, N,N′-bis-(4-isopropylbenzaldimine)-1,2-diaminoethane (L), obtained by the condensation of 4-isopropylbenzaldehyde and 1,2-diaminoethane, has been used to synthesize the complexes of the type [ML₂X₂] [M = Co(II), Ni(II) and Zn(II); X = Cl and OAc]. The newly synthesized ligand (L) and its complexes have been characterized on the basis of elemental analyses, mass, ¹H and ¹³C-NMR, molar conductance, IR, UV–vis, magnetic moment, CV and thermal analyses, powder XRD and SEM. IR spectral data show that the ligand is coordinated to the metal ions in a bidentate manner. The geometrical structures of these complexes are found to be octahedral. Interestingly, reaction with Cu(II) ion with this ligand undergoes hydrolytic cleavage to form ethylenediamine copper(II) complex and the corresponding aldehyde. The antimicrobial results indicate that the chloro complexes exhibit more activity than the acetato complexes. The complexes bind to CT–DNA by intercalation modes. Novel chloroform soluble ZnL₂Cl₂ complex exhibits tremendous antimicrobial, DNA binding and cleaving properties.     

Antibacterial activity of transition metal complexes with a tridentate NNO amoxicillin derived Schiff base. Synthesis and characterization

From the reaction of amoxicillin ( 1 ) antibiotic with 2,6?diaminopyridine ( 2 ) an amoxicillin?based Schiff base (HL) ( 3 ) was obtained and its transition metal Schiff base complexes were synthesized. Spectroscopic and physicochemical techniques, namely, UV?Vis, FT?IR, ¹H?NMR, EPR, mass spectrometry, molar conductance, magnetic susceptibility, molecular modelling, together with elemental and thermal analyses, were used to characterize the synthesized compounds. Spectral and magnetic data suggested an octahedral geometry for all the complexes and the general formulae [ML(H₂O)₃][PF₆] (M(II) = Mn²⁺ ( 4 ), Co²⁺ ( 5 ), Ni²⁺ ( 6 ), Cu²⁺ ( 7 ), Zn²⁺ ( 8 ), was proposed for them, where L represents deprotonated tridentate NNO amoxycillin?derived Schiff base. All compounds were screened for antibacterial activity by using agar disc diffusion method. The zinc(II) complex exhibited promising bactericidal activity against E. coli and S. aureus.     

Copper(II), cobalt(II), nickel(II) and zinc(II) complexes of Schiff base derived from benzil-2,4-dinitrophenylhydrazone with aniline

New Schiff base chelates of Cu(II), Co(II), Ni(II) and Zn(II) derived from benzil-2,4-dinitro-phenylhydrazone with aniline have been synthesised. Microanalytical data, molar conductance, and magnetic susceptibility values have been obtained, and IR,¹H NMR,¹³C NMR, UV-Vis, CV and EPR spectral studies have been carried out to suggest tentative structures for the complexes     

Antibacterial activity of transition metal complexes containing a tridentate NNO phenoxymethylpenicillin‐based Schiff base. An anti‐MRSA iron (II) complex

Transition metal complexes containing a phenoxymethylpenicillin‐derived Schiff base (HL) 3 obtained from the condensation of phenoxymethylpenicillin (PMP) 1 , with 1,2‐diaminobenzene 2 , were prepared. Spectroscopic and physicochemical techniques, namely, UV–Vis, FT‐IR, ¹H‐NMR, EPR, mass spectrometry, magnetic susceptibility, molar conductance, DFT studies, together with elemental and thermal analyses were used to characterize the synthesized complexes. Based on the characterization studies, the general formulae [ML (OAc)(H₂O)₂] where M = Fe 4 , Co 5 , Ni 6 , Cu 7 , and Zn 8 , were proposed for the complexes. The Schiff base ligand 3 behaved as a monoanionic tridentate NNO chelating agent. On the basis of magnetic and spectral data an octahedral geometry for all the complexes was suggested. Schiff base ligand 3 , and the metal complexes 4 – 8 were tested against G(+) or bactericidal activity by agar disc diffusion method and minimal inhibitory concentration (MIC). The results were compared with the activity of the standard drug PMP 1 . In vitro bacterial viability revealed that 3  had similar activity than 1 and exhibited modification in its bactericidal activity when formed metal complexes. It was found that the complexes 4 , 6 and 7 exhibited much better bactericidal activity than 1 against methicillin‐resistant Staphilococcus Aureus (MRSA) being complex 4 the most promising compound showing a MIC value of 0.042 μmol/ml.     

Study on the nematicidal activity and chemical structure of NO bidentate Schiff base some metal complexes

A series of Co(II), Cu(II), Y(III), Zr(IV), La(III), and U(VI) complexes derived from 2-(2-hydroxybenzylidinemine)-benzoic acid (L) ligand were synthesized. The mode of bonding of L and the structure of its metal complexes were investigated using different analytical and spectral tools (FT-IR, UV–Vis, ¹H NMR, mass, and XRD). The ligand chelated with the metal ions as a neutral bidentate through oxygen and azomethine nitrogen atoms. All metal complexes adopted octahedral geometry with characteristic color for metal ions. The results of magnetic moment measurements supported paramagnetic for some complexes (Co(II) and Cu(II)) and diamagnetic phenomena for the other complexes. The thermal decomposition of the ligand along with its metal complexes was explained. The molar conductance values of all complexes in (DMF) were found in the range 154.50 to 250.20 S cm² mol⁻¹ at room temperature. The activation thermodynamic parameters, such as E*, ΔH*, ΔS* and ΔG*, were calculated from the DTG curves using Coats–Redfern (CR) and Horowitz–Metzeger (HM) methods at n = 1 or n ≠ 1. The nematicidal activity of the synthesized L and their metal complexes was screened.     

Metal‐based antitumor,cytotoxic and antimicrobial activity: pharmacological evaluation of Knoevenagel condensate β‐diketone Schiff base thiosemicarbazone Cu(II) and Zn(II) complexes

Knoevenagel condensate Schiff base ligands [L = 3‐cinnamalideneacetylacetone‐thiosemicarbazone (CAT)/3‐cinnama‐ lideneacetylacetoneethylthiosemicarbazone (CAET)/3‐cinnamalideneacetylacetonephenylthiosemicarbazone (CAPT)] and their copper/zinc complexes were synthesized. They were characterized by analytical and spectral techniques. From these data it was found that the ligands adopt square‐planar geometry on metalation with Cu²⁺ and Zn²⁺. To evaluate the antitumor and cytotoxic activity of the synthesized complexes in mice and human cancer cell lines, the antitumor activity of the complexes was evaluated against an Ehrlich ascites carcinoma (EAC) tumor model. The activity was assessed using survival time and short‐term in vitro cytotoxic activity. Oral administration of complexes (100 mg/kg) increased the survival time. The cytotoxic activity of complexes was evaluated using human breast cancer (MDA‐MB‐231), colon cancer (HCT‐116) and nonsmall lung cancer (NCI‐H‐23) cell lines. Both the complexes possessed significant antitumor and cytotoxic activity on EAC and human cancer cell lines. The in vitro antimicrobial screening effect of the investigated compounds was also tested against the various organisms by well diffusion method. Copyright © 2009 John Wiley & Sons, Ltd.     

Design, synthesis, spectroscopic characterization, biological screening, and DNA nuclease activity of transition metal complexes derived from a tridentate Schiff base

A new series of transition metal complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Cd(II), Hg(II), and VO(IV) have been designed and synthesized from the Schiff base derived from cinnamidene-4-aminoantipyrine and 2-aminophenol by involving the carbonyl group of 4-aminoantipyrine. The structural features have been arrived from their elemental analyses, magnetic susceptibility, molar conduction, FAB mass, IR, UV-Vis, ¹H NMR and ESR spectral studies. The data show that the complexes have composition of the ML₂ type. The UV-Vis, magnetic susceptibility, and ESR spectral data of the complexes suggest an octahedral geometry around the central metal ion except the VO(IV) complex, which has a square-pyramidal geometry. The redox behavior of the copper and vanadyl complexes has been studied by cyclic voltammetry. The antimicrobial activity of the ligand and its complexes has been extensively studied on microorganisms such as Salmonella typhi, Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Aspergillus niger, and Rhizoctonia bataicola. It has been found that most of the complexes have higher activities than that of the free ligand. The nuclease activity of the above metal complexes shows that the complexes cleave DNA through redox chemistry. In the presence of H₂O₂, the complexes are capable of cleaving calf thymus DNA. The text was submitted by the authors in English.     

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.     

Spectral characterization,electrochemical, antimicrobial and cytotoxic studies on new metal(II) complexes containing N2O4 donor hexadentate Schiff base ligand

We report the biological activity of the new Schiff base ligand H₂L (H₂L = 6,6′-((1E,11E)-5,8-dioxa-2,11-diazadodeca-1,11-diene-1,12-diyl)bis(2,4-dichlorophenol)), its derived metal(II) complexes [Cu(L)] (1), [Co(L)] (2), [Ni(L)] (3) and [Zn(L)] (4), along with their structural characterizations by using various analytical and spectroscopic techniques. Electrochemical investigations showed that all of these Cu(II), Co(II) and Ni(II) complexes were reversibly reducible. Although the change of the number of unpaired electrons are different of the metal cations, they have an effect on the redox potentials of the Co(II)/(I), Ni(II)/(I) and Cu(II)/(I) couples. The ¹H NMR and FTIR data concluded that the Schiff base ligand H₂L acts as a hexadentate ligand coordinating with metal(II) ions through the oxygen atoms of the (COC), phenolic (COH) groups and nitrogen atom of the azomethine (CHN) group. UV-Visible absorption spectra studies clearly revealed the octahedral geometry of the prepared metal(II) complexes. Complexes 1 and 4 were found to be efficient in bringing about antimicrobial activities. The proposed mechanism of their antimicrobial activities has been discussed. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed the remarkable cytotoxicity of complex 1 (IC50 = 17 ± 1.3 μg/mL) on human breast cancer MCF-7 cells than Schiff base ligand H₂L and complexes 2–4. Moreover, AO/EB staining assay revealed cell death due to apoptosis in MCF-7 cells and the generation of ROS by the Schiff base ligand H₂L and its derived metal(II) complexes 1–4 may be a possible cause for their cytotoxic activity.     

In vitro antimicrobial and antioxidant evaluation of rare earth metal Schiff base complexes derived from threonine

Six novel Ln(III) Schiff base complexes were synthesized using rare earth metals with threonine and 5‐bromosalicylaldehyde, namely Pr(III), Sm(III), Gd(III), Tb(III), Er(III) and Yb(III) Schiff bases. These complexes were characterized using elemental analysis, molar conductivity, Fourier transform infrared and UV–visible spectroscopies, and thermogravimetry–differential thermal analysis. The general formula of the complexes is [Ln(L)(NO₃)₂(H₂O)].NO₃ (L = Schiff base ligand). The spectroscopic data reveal that the Schiff base ligand behaves as a tridentate ligand with ONO donor atoms sequencing towards the central metal ion. An investigation of fluorescence properties of the Sm(III), Er(III) and Tb(III) complexes shows that the Ln(III) ions can be sensitized efficiently by the ligand to some extent. Antimicrobial activity testing indicates that all six complexes exhibit antibacterial and antifungal ability against microbes with broad antimicrobial spectra. In addition, the antioxidant properties of the complexes were also screened. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis,characterization, and anticancer activity of some metal complexes with a new Schiff base ligand

A new Schiff base ligand, 2-((E)-((4-(((E)-benzylidene)amino)phenyl)imino)methyl)-naphthalene-1-ol, was prepared by the reflux condensation of p-phenylenediamine with 2-hydroxy-1-naphthaldehyde and benzaldehyde. Metal complexes were prepared by reacting the ligand with metal salts: VCl₃, CrCl₃·6H₂O, MnCl₂·3H₂O, FeCl₃·6H₂O, CoCl₃·6H₂O, NiCl₂·6H₂O, CuCl₂·2H₂O, and ZnCl₂. The ligand and its metallic complexes were characterized by various techniques such as elemental analysis, AAS, NMR, IR, UV–Vis, TGA, DTA, XRD and TEM. The data confirmed that the ligand coordinated with the metal ions in a bidentate nature, bonding through its azomethine nitrogen atom and phenolic oxygen atom; this gave an octahedral geometry. The XRD patterns of the complexes indicated that they were of various structures: the Mn(II), Co(III), and Cu(II) complexes were triclinic, the ligand and Ni(II) complex were orthorhombic, the V(III) and Zn(II) complexes were hexagonal, the Cu(II) complex was monoclinic, and the Fe(II) complex was cubic. TEM analysis confirmed that the complexes were nanoscale in nature. The antibacterial and antifungal activities of the ligand and its complexes against Salmonella enterica serovar typhi and Candida albicans were investigated by the hole plate diffusion method. It was observed that the Co(II) and Zn(II) complexes had intermediate antibacterial activities, while the V(III) complex had the highest activity against C. albicans fungi. The in vitro anticancer activities of the ligand and its metal complexes were tested towards PC-3, SKOV3, and HeLa tumour cell lines, where they exhibited higher antitumour activities against these selected human cell lines than clinically used drugs such as cisplatin, estramustine, and etoposide.     

Synthesis,characterization, electrochemical,catalytic and antimicrobial activity studies of hydrazone Schiff base ruthenium(II) complexes

Four tridentate O, N, O donor Schiff base ligands were prepared by the reaction of substituted benzhydrazide and appropriate salicylaldehyde. The complexes of these ligands were synthesized by refluxing the ligands with ruthenium(II) starting complexes of the formula [RuHCl(CO)(EPh₃)₂B] in benzene, where E = P or As; B = PPh₃ or AsPh₃ or pyridine. The newly synthesized complexes were characterized by elemental, spectral (FT‐IR, UV and NMR) and electrochemical data. On the basis of the above studies, an octahedral structure has been proposed for all the complexes. The catalytic efficiency of the complexes in aryl–aryl couplings and oxidation of alcohols was examined and their inhibition activity against the growth of the micro‐organisms was also examined. Copyright © 2009 John Wiley & Sons, Ltd.