Free Schiff Base Ligand Research Articles

Syntheses, crystal structures and photo physical aspects of azido-bridged tetranuclear cadmium (II) complexes: DFT/TD-DFT, thermal, antibacterial and anti-biofilm properties

In this work we have reported two novel tetranuclear Cd(II) complexes viz. [Cd4 (LOMe)2 (μ1,1-N3)3 (μ1,3-N3)]n (1) and [Cd4 (LOEt)2 (μ1,1-N3)3(OAc)]2 (2) where (H2LOMe) and (H2LOEt) are two important less explored salen-type Schiff base ligands. Both of the complexes have been characterized by using routine spectroscopic techniques, elemental analyses (C, H and N), X-ray powder diffraction pattern (PXRD) and thermal analysis by TGA along with single x-ray crystallography. The complete structural study discloses that in both cases the fully deprotonated ligand [LOMe]2- or [LOEt]2- utilized all potential coordination sites to accommodate four Cd(II) ions. Complex 1 is a one-dimensional polymer with azide (N3) linkage having both (μ1,1 end on) and (μ1,3 end-to-end) azido bridging but complex 2 is a discrete octanuclear ensamble where two [Cd4(O)4(N)2]2+ units bridged to each other showing μ1,1 end on end on azide bridging. Exploration of photo physical properties in DMSO solvent reveals that Cd(II) complexes enhance appreciably the fluorescence behavior over free Schiff base ligands (H2LOMe) and (H2LOEt). DFT calculations performed at B3LYP/def2-TZVP level of theory reveal both the energetics and composition of FMOs in these complexes and also show electrophilic and nucleophilic areas via molecular electrostatic maps [ESP] concept. The antibacterial, membrane damage assay and anti-biofilm properties of complexes 1 and 2 were investigated very carefully against some important Gram-positive and Gram-negative bacterial strains.

Coordination-Mediated Synthesis of 67Ga-Labeled Purification-Free Trivalent Probes for in Vivo Imaging of Saturable Systems.

A large excess of unlabeled ligands over gallium-67 (67Ga) provides 67Ga-labeled probes with high radiochemical yields in a short reaction time. However, the unlabeled ligands hinder target accumulation of radiolabeled probes by competing for target molecules. To circumvent the problem, we investigated the way to prepare 67Ga-labeled multivalent probes from monovalent ligands. The reaction of a bi- or tridentate ligand with [67Ga]Ga-citrate resulted in 67Ga-labeled probes of insufficient stability. However, the reaction of [67Ga]Ga-citrate with a mixture of RGD-conjugated salicylaldehyde and triamine provided a 67Ga-labeled trivalent probe with stability sufficient for in vivo applications. Since the free Schiff base ligand decomposed rapidly upon injection, the 67Ga-labeled trivalent probe visualized the murine tumor without postlabeling purification, which was not achieved with a 67Ga-labeled trivalent probe from a trivalent ligand. These findings indicate the availability of Schiff base ligands to prepare 67Ga-labeled trivalent probes by a simple radiolabeling procedure.

Copper(II) complexes with isoxazole Schiff bases: Synthesis, spectroscopic investigation, DNA binding and nuclease activities, antioxidant and antimicrobial studies

Three novel Cu(II) complexes 1 [Cu(L1)2], 2 [Cu(L2)2] and 3 [Cu(L3)2], where L1H = 2-((3,4-dimethylisoxazol-5-ylimino)methyl)-6-tert-butylphenol, L2H = 2-((3,4-dimethylisoxazol-5-ylimino)methyl)-4,6-di-tert-butylphenol and L3H = 2-((3,4-dimethylisoxazol-5-ylimino)methyl)-4,6-dibromophenol were synthesized and characterized by elemental analysis, FT-IR, UV–Visible, 1H NMR, 13C NMR, ESI mass, EPR and magnetic susceptibility studies. Based on spectroscopic and analytical data, a square planar geometry is assigned for all complexes. DNA binding and cleavage studies against calf thymus DNA (CT-DNA) and supercoiled pBR322 DNA respectively revealed an intercalative mode of binding and also cleave pBR322 DNA in an efficient manner. The ligands and their complexes were examined for antimicrobial activity against bacterial species E. coli, B. subtilis and fungal species S. rolfsii and M. phaseolina and found that all the Cu(II) complexes show more activity than the free Schiff base ligands. The antioxidant activity of metal complexes have also been determined using DPPH assay and found that the complexes are found to be good free radical scavengers.

Syntheses, crystal structures, antioxidant SOD-like properties and in-vitro antimicrobial studies of Cu(II) and Ni (II) complexes with 2-((E)-(4-bromo-2-chlorophenylimino) methyl)-6-bromo-4-nitrophenol and (E)-1-(3, 5-dichloro-2-hydroxybenzylidene)-4, 4-dimethylthiosemicarbazide

Three new salen-type copper (II) and nickel (II) complexes viz. [Cu(L)2] (1); [Ni(L)2] (2); [Ni(L1) (DMF)] (3), where HL = 2-((E)-(4-bromo-2-chlorophenylimino) methyl)-6-bromo-4-nitrophenol and HL1= (E)-1-(3,5-dichloro-2-hydroxybenzylidene)-4,4-dimethylthiosemicarbazide; DMF = N, N-dimethylformamide, have been successfully achieved and structurally characterized by single crystal X-ray analysis. The salen-type ligands (HL and HL1) are able to provide the most plausible geometry for 1:2 complexes which appeared to be a square planar (four coordinated) geometry around the M (II) ions. The FT-IR spectra, UV–Vis spectra and magnetic susceptibility measurements agree with the observed crystal structures. X-band Electron paramagnetic resonance (EPR) spectra indicate a dx2–y2ground state (g||>g⊥> 2.0023 and A||>A⊥) for (1) at RT and LNT. The salen-type ligands were behaves as monobasic bidentate-N, O ligand (HL) or tridentate ligand (HL1) possessing N, O and S donor atoms. Electrochemical properties for complexes (1)-(3) yielded an irreversible couple that can be assigned to an M (II)/M (I) redox process. These complexes exhibit effective antioxidant activity towards the dismutation of superoxide anions. The complex (1) exhibits more active scavenging effects against O2− than HL and other complexes (2) and (3) under the same conditions. These complexes were also tested for their in vitro microbiological screening activities against two bacteria (Streptococcus aureus, Escherichia coli) and two fungi (Aspergillus sp., Penicillium sp.) comparing with the salen-type ligands and the control. The biological property of salen-type complexes at the minimum inhibitory concentration (MIC) indicates that most of the metal chelates exhibits slightly higher antimicrobial activity than the free Schiff base ligands.

Studies of Ni(II) and Cu(II) complexes with schiff base derived from salicylaldehyde and aniline

The schiff base ligand and its complexes of divalent metal ions of Ni (II) and Cu (II) were synthesized. The ligand and the complexes were characterized by elemental analysis, potentiometry, molar conductance, melting point or decomposition temperatures and infrared analyses. The elemental analysis data show the formation of 1:2 metal-ligand ratio. The ligand and complexes were screened for antibacterial activity against Escherichia coli and Staphylococcus aureus , and antifungal activity against Aspergillums niger and Candida albican , using discs diffusion method. It has been found that the ligand and the complexes showed different activities against microorganisms. The complexes show higher activity than the free Schiff base ligand. The molar conductance of the complexes measured is low, indicating their non-electrolytic nature. The potentiometric studies of the complex compounds revealed 1:2 metal to ligand ratio. Keywords: salicylaldehyde, aniline, ligand, potentiometry, antibacterial, antifungal

Synthesis, crystal structure and biological studies of new hydrazone ligand, 2-(Methoxycarbonyl-hydrazono)-pentanedioic acid and its silver(I) complex

Abstract A new hydrazone ligand (2-(Methoxycarbonyl-hydrazono)-pentanedioic acid, H2L), derived from methyl carbazate and α-ketoglutaric acid, and its Ag(I) complex [Ag(HL)(H2L)] were synthesised and characterised by elemental, spectral and thermal analyses. The X-ray structures of the ligand and complex were determined. The silver ion is hexa-coordinated to two tridentate (O, N, O) hydrazone ligands in a distorted octahedral environment. The binding carboxylic acid group is protonated in one of the ligands (netural) while it is present as the carboxylate in the other (negatively charged) ligand. The bulk material of the complex thermally decomposes to form metallic silver sheets. The ability to scavenge radical of both, the ligand and complex, was studied against these radicals: DPPH , ABTS +, NO , O2 −. The binding affinity and mode of binding towards CT-DNA were recorded by UV-absorption and the ethidium bromide displacement method. The interaction of ligand and complex with bovine serum albumin was investigated using UV–Vis, fluorescence and synchronous spectroscopic methods. The silver complex showed strong binding propensity than the free Schiff base ligand in binding studies. The antimicrobial activity was studied against both bacteria and fungi strains and the silver complex exhibited significant activity as compared to the ligand alone. Significantly high antimicrobial activity was noticed especially for Staphylococcus aureus, and Escherichia coli which were extensively studied by MIC methods. Furthermore, the ligand and complex show potential cytotoxicity towards the MCF-7 breast cancer cell line. Both of them have been found to induce apoptosis confirmed by AO/EtBr and DAPI staining assays.

Synthesis, spectroscopic, thermal analyses, biological activity and molecular docking studies on mixed ligand complexes derived from Schiff base ligands and 2,6‐pyridine dicarboxylic acid

Two novel Schiff base ligands (La and Lb) were prepared from the condensation of quinoline 2‐aldehyde with 2‐aminopyridine (ligand La) and from the condensation of oxamide with furfural (ligand Lb). Mixed ligand complexes of the type M+2La/b Lc were prepared, where (La and Lb) the primary ligands and Lc was 2,6‐pyridinedicarboxylic acid as secondary ligand. Metal ions used were Fe(II), Co(II), Ni(II) and Zn(II) for mixed ligands La Lc and Fe(II), Co(II), Ni(II), Cu(II), Hg(II) and Zn(II) for LbLc mixed ligands. La and Lb Schiff base ligands were both characterized using elemental analyses, molar conductance, IR, 1H and 13C NMR. Mass spectra for Lb, [Zn(La)LcCl]Cl and [Cu(Lb)LcCl]Cl were also studied. ESR spectrum of the [Cu(Lb) LcCl]Cl complex was also recorded The metal complexes were synthesized and characterized using elemental analyses, spectroscopic (IR, 1H NMR, UV‐visible, diffused reflectance), molar conductance, magnetic moment and thermal studies. The IR and 1H NMR spectral data revealed that 2,6‐pyridinedicarboxalic acid ligand coordinated to the metal ions via pyridyl N and carboxylate O without proton displacement. In addition, the IR data showed that La and Lb ligands behaved as neutral bidentate ligands with N2 donation sites (quinoline N and azomethine N for La and two azomethine N for Lb). Based on spectroscopic studies, an octahedral geometry was proposed for the complexes. The thermal stability and degradation of the metal complexes were investigated by thermogravimetric analysis. The binding modes and affinities of La, Lb and Zn(II) complexes towards receptors of crystal structure of E. coli (PDB ID: 3 t88) and mutant oxidoreductase of breast cancer (PDB ID: 3 hb5) receptors were also studied.The antimicrobial activity against two species of Gram positive, Gram negative bacteria and fungi were tested for the Schiff base ligands, 2,6‐pyridinedicarboxylic acid and the mixed ligand complexes and revealed that the synthesized mixed ligand complexes exhibited higher antimicrobial activity than their free Schiff base ligands.

Preparation, characterization, antimicrobial and anticancer activities of Schiff base mixed ligand complexes

A new Schiff base ligand (HL) derived from quinoline-2-carboxaldehyde with 2-aminophenol (1:1 molar ratio) and its mixed ligand complexes, viz. 2,2′-bipyridine (1:1:1 molar ratio), have been synthesized and characterized by elemental analysis, spectroscopic studies, X-ray diffraction, ESR, magnetic and thermal analysis. The molar conductance measurement of mixed ligand complexes in DMF showed that Zn(II) and Cd(II) complexes were nonelectrolytes; however, Cr(III), Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) complexes were electrolytes. The transition metal complexes had octahedral geometry with a general molecular formulae [M(L)(2,2′-bipy)(H2O)]Cl x ·nH2O (M = Cr(III) (x = n = 2), Mn(II) and Co(II) (x = 1, n = 0), Ni(II) and Cu(II) (x = n = 1) and [M(L)(2,2′-bipy)Cl]Cl x ·nH2O (M = Fe(III) (x = 1, n = 3), Zn(II) (x = 0, n = 1) and Cd(II) (x = 0, n = 2)). Also, Schiff base ligand and its mixed ligand complexes were screened against Gram-positive bacteria (Streptococcus pneumoniae, Bacillus subtilis), Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli) and fungal species (Aspergillus fumigatus, Candida albicans). Gentamicin, ampicillin and amphotericin B were used as standard drugs for Gram positive, Gram negative and antifungal activity, respectively. The results showed that all mixed ligand complexes have antimicrobial activity higher than free Schiff base ligand. In addition, anticancer activity of Schiff base ligand and its mixed ligand metal complexes were also tested against breast cancer cell line (MCF-7) and colon cancer cell line (HCT-116). Cd(II) complex showed the highest IC50 against two cell lines.

Synthesis, spectroscopic, antimicrobial, XRD, fluorescence of new Ni(II), Cd(II), Hg(II) and U(VI) complexes with 1-(2-furylmethylene)-N-(3-phenylallylidene)methanamine Schiff base

The 1:1 condensation of 2-furfurylamine and cinnamaldehyde under template condition gives the Schiff base ligand 1-(2-furylmethylene)-N-(3-phenylallylidene)methanamine (L). The reaction of the ligand with Ni(II), Cd(II), Hg(II) and U(VI) ions gives a series of novel complexes formulated as [NiLCl(H2O)]Cl·1½H2O, [CdL2(H2O)2]·2NO3·½H2O, [HgL2Cl2] and [UO2L3]·2NO3·H2O. The stoichiometry of the complexes was 1:1 for Ni(II), 1:2 for both Cd(II) and Hg(II) and 1:3 (M:L) for U(VI) complexes. The molar conductance of the complexes lies in the range of 135–250 Ω−1mol−1cm2 indicating their electrolytic behavior except Hg(II) complex. Electronic spectra and magnetic moments suggested varieties of geometries around the central metal atoms. The emission spectra of these complexes indicate the luminescence characteristics of the complexes. The X-ray diffraction (XRD) patterns of Schiff base and its complexes were investigated in powder forms. Thermodynamic parameters were computed from the thermal data using Coats and Redfern method. Structural optimization of the ligand and its Ni(II), Cd(II) and Hg(II) complexes was computed using the density functional theory (DFT), where the B3LYP functional was employed. The synthesized complexes exhibited higher antimicrobial activity than its free Schiff base ligand.

Synthesis and Spectral Analysis of Some Metal Ions Complexes with Mixed Ligands of Schiff Base and 1, 10-Phenanthroline

The free Schiff base ligand (HL1) is prepared by being mixed with the co-ligand 1, 10-phenanthroline (L2). The product then is reacted with metal ions: (Cr+3, Fe+3, Co+2, Ni+2, Cu+2 and Cd+2) to get new metal ion complexes. The ligand is prepared and its metal ion complexes are characterized by physic-chemical spectroscopic techniques such as: FT-IR, UV-Vis, spectra, mass spectrometer, molar conductivity, magnetic moment, metal content, chloride content and microanalysis (C.H.N) techniques. The results show the formation of the free Schiff base ligand (HL1). The fragments of the prepared free Schiff base ligand are identified by the mass spectrometer technique. All the analysis of ligand and its metal complexes are in good agreement with the theoretical values indicating the purity of Schiff base ligand and the metal complexes. From the above data, the molecular structures for all the metal complexes are proposed to be octahedral

Synthesis and Spectral Analysis of Some Metal Ions Complexes with Mixed Ligands of Schiff Base and 1, 10-Phenanthroline

The free Schiff base ligand (HL1) is prepared by being mixed with the co-ligand 1, 10-phenanthroline (L2). The product then is reacted with metal ions: (Cr+3, Fe+3, Co+2, Ni+2, Cu+2 and Cd+2) to get new metal ion complexes. The ligand is prepared and its metal ion complexes are characterized by physic-chemical spectroscopic techniques such as: FT-IR, UV-Vis, spectra, mass spectrometer, molar conductivity, magnetic moment, metal content, chloride content and microanalysis (C.H.N) techniques. The results show the formation of the free Schiff base ligand (HL1). The fragments of the prepared free Schiff base ligand are identified by the mass spectrometer technique. All the analysis of ligand and its metal complexes are in good agreement with the theoretical values indicating the purity of Schiff base ligand and the metal complexes. From the above data, the molecular structures for all the metal complexes are proposed to be octahedral

Lanthanide(III) complexes with tridentate Schiff base ligand, antioxidant activity and X-ray crystal structures of the Nd(III) and Sm(III) complexes

The tridentate N4-type Schiff base was synthesized from the condensation reaction of 2-hydrazinopyridine and pyridine-2-carbaldehyde. Neodymium and Samarium complexes were isolated when the corresponding nitrate salt was added to the solution of the ligand. The isolated compounds were characterized by elemental analyses, IR study, room temperature magnetic measurements and single X-ray crystal diffraction of the two crystals. Both complexes crystallize in the monoclinic system with space group P21/c. The cell parameters of the Nd complex are a = 11.0927(8) A, b = 17.9926 (13) A, c=11.9395(9) A and β = 115.274(5) ° while the Sm complex shows parameters cell of a = 11.0477(8) A, b = 17.9254(13) A, c = 11.9149(8) A and β = 115.489(5) °. The X-ray study reveals isotopic Nd/Sm binuclear structures were each metal ion is nine-coordinated in the same fashion. Both metal centers have distorted tricapped trigonal prism geometry, with the Schiff base acting as tridentate ligand. The DPPH· radical scavenging effects of the Schiff base ligand and its Ln(III) complexes were screened. The Ln(III) complexes were significantly more efficient in quenching DPPH· than the free Schiff base ligand.

Synthesis, characterization, biological activities and luminescent properties of lanthanide complexes with [2-thiophenecarboxylic acid, 2-(2-pyridinylmethylene)hydrazide] Schiff bases ligand

A Schiff base L [2-thiophenecarboxylic acid, 2-(2-pyridinylmethylene)hydrazide] with its lanthanide metal complexes was synthesized. These complexes were characterized by elemental analysis, molar conductivity measurements, spectral analysis (NMR, FT-IR, and UV-Vis), luminescence and thermal gravimetric analysis. The Schiff base ligand was a tridentate chelate and coordinates to the central lanthanide ion with 1:2 metal:ligand ratio. The conductivity data showed a 1:1 electrolytic nature with a general formula [LnL2(NO3)2]NO3. The luminescence emission properties for Sm, Tb, and Eu complexes were observed and showed that the ligand L could absorb and transfer energy to Sm(III), Tb(III) and Eu(III) ions. The complexes possessed a good antibacterial activity against different bacterial strains. In addition, the scavenging activity of the Ln(III) complexes on DPPH was concentration dependant and the complexes were significantly more efficient in quenching DPPH than the free Schiff base ligand.

Synthesis, physical characterization, antibacterial activity and thermodynamic studies of five coodrdinate cobalt(III) Schiff base complexes

Some five-coordinated cobalt(III) complexes were synthesized and characterized using elemental analysis, 1 H NMR and IR spectra. The formation constants and the thermodynamic parameters were measured spectrophotometrically for the 1:1 adduct formation of [Co(Chel)(PBu 3 )]ClO 4 .H 2 O where Chel = cd3OMesalen, cd4OMesalen, cd5OMesalen: methyl-2-{[1-methyl-2-(2-hydroxy-3-, 4-, 5-methoxyphenyl)methylidynen-itrilo]ethyl}amino-1-cyclopentene-dithiocarboxylate, as acceptors, with some linear and cyclic amines as donors, in different solvents at constant ionic strength (I = 0.1 M NaClO 4 ), and at various temperatures (T = 283-313 K). The results revealed that the formation constants of the Co(III) Schiff base complexes toward a given amines donor are as follow: [Co(cd4OMesalMeen)(PBu 3 )] + > [Co(cd3OMesalMeen)(PBu 3 )] + > [Co(cd5OMesalMeen)(PBu 3 )] + . The trend of the formation constants of the donors (amines) toward a given cobalt(III) complex is as follow: Im > 4-MeIm > BzIm and n-butylamine > sec-butylamine > tert-butylamine. Also the effect of the solvents on the formation constants of a given cobalt(III) Schiff base complex toward a given donor are as follow: CH 3 CN > DMF > EtOH. The ligands and their cobalt complexes have been screened for their antibacterial activities. All the free Schiff base ligands exhibit higher antibacterial activity than the cobalt(III) complexes. KEY WORDS : Cobalt (III) Schiff base complex, Thermodynamic parameters, Amines, Antibacterial activity Bull. Chem. Soc. Ethiop. 2016 , 30(2), 209-220. DOI: http://dx.doi.org/10.4314/bcse.v30i2.5

Metal-based biologically active azoles and β-lactams derived from sulfa drugs

Metal complexes of Schiff bases derived from sulfamethoxazole (SMZ) and sulfathiazole (STZ), converted to their β-lactam derivatives have been synthesized and experimentally characterized by elemental analysis, spectral (IR, 1H NMR, 13C NMR, and EI-mass), molar conductance measurements and thermal analysis techniques. The structural and electronic properties of the studied molecules were investigated theoretically by performing density functional theory (DFT) to access reliable results to the experimental values. The spectral and thermal analysis reveals that the Schiff bases act as bidentate ligands via the coordination of azomethine nitrogen to metal ions as well as the proton displacement from the phenolic group through the metal ions; therefore, Cu complexes can attain the square planner arrangement and Zn complexes have a distorted tetrahedral structure. The thermogravimetric (TG/DTG) analyses confirm high stability for all complexes followed by thermal decomposition in different steps. In addition, the antibacterial activities of synthesized compounds have been screened in vitro against various pathogenic bacterial species. Inspection of the results revealed that all newly synthesized complexes individually exhibit varying degrees of inhibitory effects on the growth of the tested bacterial species, therefore, they may be considered as drug candidates for bacterial pathogens. The free Schiff base ligands (1–2) exhibited a broad spectrum antibacterial activity against Gram negative Escherichia coli, Pseudomonas aeruginosa, and Proteus spp., and Gram positive Staphylococcus aureus bacterial strains. The results also indicated that the β-lactam derivatives (3–4) have high antibacterial activities on Gram positive bacteria as well as the metal complexes (5–8), particularly Zn complexes, have a significant activity against all Gram negative bacterial strains. It has been shown that the metal complexes have significantly higher activity than corresponding ligands due to chelation process which reduces the polarity of metal ion by coordinating with ligands.

Persistent DNA binding, cleavage performance and eco-friendly catalytic nature of novel complexes having 2-aminobenzophenone precursor

This paper describes the synthesis of four novel bidentate metal(II) complexes having 2-aminobenzophenone precursor and a co-ligand (anthranilic acid). They are characterized by the usual spectral and analytical data. They adopt octahedral geometrical arrangements around the metal ions which have been confirmed by electronic absorption data. Moreover, the EPR study of Cu(II) complex has provided supportive evidence to the conclusion drawn on the basis of electronic spectrum and magnetic moment value. Powder XRD and SEM studies show that all the complexes are microcrystalline with homogenous morphology. The interaction of these complexes with CT-DNA has been explored by UV-absorption, fluorescence, viscosity, CV and CD techniques which reveal that the complexes could bind to CT-DNA through intercalation. The oxidative cleavage of the metal complexes with pBR322 DNA has also been investigated by gel electrophoresis. Moreover, the antimicrobial bustle shows that all metal chelates have superior activity than the free Schiff base ligand. The catalytic activity of the complexes has been evaluated towards the oxidation of aniline. All the complexes exhibit significant catalytic activity. Among them Cu(II) complex exhibits better catalytic activity than others. This catalytic process occurs at room temperature and it proceeds in water medium which suggests that this is an eco-friendly process.

SYNTHESIS, SPECTRAL CHARACTERIZATION AND THERMAL BEHAVIOUR OF NEW METAL(II) COMPLEXES WITH SCHIFF BASE DERIVED FROM AMOXICILLIN

ABSTRACT Metal complexes of Schiff base derived from different antibiotics are widely employed as biological active materials, especially as antibacterial agents. Two new metal (II) complexes with the Schiff, base (HL) derived from amoxicillin and salicylaldehyde were synthesized and investigated using elemental analysis, spectroscopic techniques (IR and UV-Vis), conductometric and magnetic measurements. The IR spectra illustrated a bidentate ligand which coordinates through phenolic oxygen atom and imino nitrogen atom from azomethine bond. UV-Vis spectrophotometry showed the characteristic adsorption bands corresponding to an octahedral geometry for both metal complexes. The general formula established from experimental data was found to be [ML 2 (H 2 O) 2 ] (M=Co(II) and Ni(II)). This composition was further confirmed by thermal analysis and their thermal stability in nitrogen atmosphere was investigated. Antibacterial study showed that the efficiency of metal complexes is higher than the one found for the free Schiff base ligand.

Polymer-anchoring Schiff base ligands and their metal complexes: Investigation of their electrochemical, photoluminescence, thermal and catalytic properties

In this study, we prepared three polymer-anchored Schiff base ligands and their Cu(II), Co(II) and Ni(II) transition metal complexes. For this purpose, we synthesized three Schiff base ligands from the reaction of 2,4-dihydroxybenzaldehyde with diamines in the ethanol solution and characterized by the analytical and spectroscopic methods. We investigated the electrochemical and photophysical properties of the free Schiff base ligands in different solvents and concentrations. In the electrochemical studies, we found that the ligands show the reversible and irreversible redox processes. In order to obtain the polymer-anchored ligands, we used Merrifield’s peptide resin (PS) as solid support. The surface morphologies of the polymer anchored Schiff base ligands were done with the scanning electron microscopy (SEM). We did alkene epoxidation and alkane oxidation reactions of the metal complexes and used the cyclohexene, styrene, cyclohexane and cyclooctane as the substrate and they show the low catalytic activity. The metal complexes have no selectivity in the oxidation reactions. The polymer anchored Schiff base ligands and their metal complexes have high thermal stability at the higher temperatures.

Coordination behavior of new bis Schiff base ligand derived from 2-furan carboxaldehyde and propane-1,3-diamine. Spectroscopic, thermal, anticancer and antibacterial activity studies

Novel bis Schiff base ligand, [N1,N3-bis(furan-2-ylmethylene)propane-1,3-diamine], was prepared by the condensation of furan-2-carboxaldehyde with propane-1,3-diamine. Its conformational changes on complexation with transition metal ions [Co(II), Ni(II), Cu(II), Mn(II), Cd(II), Zn(II) and Fe(III)] have been studied on the basis of elemental analysis, conductivity measurements, spectral (infrared, 1H NMR, electronic), magnetic and thermogravimetric studies. The conductance data of the complexes revealed their electrolytic nature suggesting them as 1:2 (for bivalent metal ions) and 1:3 (for Fe(III) ion) electrolytes. The complexes were found to have octahedral geometry based on magnetic moment and solid reflectance measurements. Thermal analysis data revealed the decomposition of the complexes in successive steps with the removal of anions, coordinated water and bis Schiff base ligand. The thermodynamic parameters were calculated using Coats–Redfern equation. The Anticancer screening studies were performed on human colorectal cancer (HCT), hepatic cancer (HepG2) and breast cancer (MCF-7) cell lines. The antimicrobial activity of all the compounds was studied against Gram negative (Escherichia coli and Proteus vulgaris) and Gram positive (Bacillus vulgaris and Staphylococcus pyogones) bacteria. It was observed that the coordination of metal ion has a pronounced effect on the microbial activities of the bis Schiff base ligand. All the metal complexes have shown higher antimicrobial effect than the free bis Schiff base ligand.

Synthesis, characterization, DNA binding, DNA cleavage and antimicrobial studies of Schiff base ligand and its metal complexes.

A series of Cu(II), Ni(II), Co(II), Mn(II) and Zn(II) complexes have been synthesized from the Schiff base ligand L. The Schiff base ligand 4-chloro-2-((4-oxo-4H-chromen-3yl) methylene amino) benzoic acid (L) has been synthesized by the reaction between chromone-3-carbaldehyde and 4-chloro-2-amino benzoic acid. The nature of bonding and geometry of the transition metal complexes as well as ligand L have been deduced from elemental analysis, FT-IR, UV-vis, (1)H NMR, (13)C NMR, ESR spectral studies, mass, magnetic susceptibility and molar conductance measurements. The complexes are found to have ML2 composition and are neutral in DMSO. Based on elemental, conductance and spectral studies, six-coordinated geometry was assigned for these complexes. The ligand L acts as tridentate and coordinates through nitrogen atom of azomethine group, hydroxyl of the carboxyl group and oxygen atom of keto group of γ-pyrone ring. The interaction of Cu(II) complex with CT-DNA was carried out by UV-vis, fluorescence titrations and viscosity measurements. The complex binds to DNA through intercalative binding mode. The nuclease activity of the above metal complexes shows that Cu(II) and Co(II) complexes cleave DNA through redox chemistry. The biological activity of the ligand and its complexes have been studied on four bacteria E. coli, B. subtilis, pseudomonas and Edwardella and two fungi penicillium and trichoderma by well disc and fusion method and found that the metal complexes are more active than the free Schiff base ligand.