Pyrazole-based azo-metal(II) complexes as potential bioactive agents: synthesis,characterization, antimicrobial,anti-tuberculosis,and DNA interaction studies

Abstract

In the present investigation, the bioactive azo-dye ligand 1,5-dimethyl-4-[(3-methyl-5-oxo-1-phenyl-4,5-dihydro-1H-pyrazol-4-yl)diazenyl]-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (L) and its transition metal complexes have been synthesized and characterized by various physical and spectroscopic techniques to elucidate their geometrical structures. The molar conductivity measurements confirmed the non-electrolytic nature of the complexes. EPR spectroscopy indicated that the metal complexes are monomeric in nature and exhibited octahedral geometry. The redox behavior of the copper complex was studied by the cyclic voltammetric technique in DMF solution and the complex showed well-established redox behavior at a scan rate of 0.05 V s^?1. The antimicrobial activity of the ligand and its metal complexes were screened against Escherichia coli, Bacillus subtilis, Aspergillus niger, and Candida albicans, and the results indicated increased activity after coordination of the ligand to the metal ions. The metal complexes exhibited enhanced antitubercular activity after chelation against M. tuberculosis. The DNA-binding experiments showed that the ligand and its metal complexes showed effective binding properties through intercalative mode against CT-DNA. All the synthesized molecules showed partial cleavage of supercoiled plasmid pUC18 DNA.     

Novel Schiff base metal complexes: synthesis,characterization, DNA binding,DNA cleavage and molecular docking studies

A novel Schiff base, 3-(((1H-1,2,4-triazol-3-yl)imino)methyl)-4H-chromen-4-one (L) was synthesized and used as ligand for the synthesis of Co(II), Ni(II), Cu(II), Zn(II) and Pd(II) complexes. The structural characterization of the ligand and its metal complexes was determined by using various physicochemical and spectroscopic methods. The IR data show that the Schiff base ligand acts as a bidentate donor coordinating through the oxygen atom of the chromone and nitrogen atom of the imine group. Based on all spectral data, tetrahedral geometry has been proposed for all the metal complexes except Cu(II) and Pd(II) complexes. However, square-planar geometry has been proposed for Cu(II) and Pd(II) complexes. DNA binding interaction of the ligand and its metal complexes was investigated by using UV–visible absorption, fluorescence and molecular docking studies. The binding constants were in the order of 10⁴ M^?1 suggesting good binding affinity towards CT-DNA. The DNA cleavage activity of the synthesized compounds was investigated by using agarose gel electrophoresis. In vitro antimicrobial activity of the synthesized compounds were screened against two gram-positive bacteria (Bacillus subtilis, Staphylococcus aureu) and two gram-negative bacteria (Escherichia coli, Proteus vulgaris) and one fungi strain Candida albicans using disc diffusion method. Antioxidant activity was carried out by DPPH radical scavenging method. In vitro anti-proliferative activity of the ligand and its metal complexes was also carried on the HEK-293, HeLa, IMR-32 and MCF-7 cancer cell lines using MTT assay.     

Studies on the manganese and copper complexes derived from chiral Schiff base: synthesis,structure, cytotoxicity and DNA/BSA interaction

Abstract

Three new manganese and copper complexes, [Mn(ONO-(S)L¹)₂] (1), [Cu(ONO-(R)L²)]₄·2CH₃OH (2), and [Mn₃(ONO-(S)L³)₄(OAc)₄(H₂O)₂] (3), {[H₂L¹ = (S)-2-phenyl-2-(2-hydroxy-5-chlorobenzylideneamino)ethane-1-ol], H₂L² = (R)-2-(2-hydroxy-5-chlorobenzylideneamino)butane-1-ol] and H₂L³ = (S)-2-phenyl-2-(2-hydroxy-3-methoxybenzylideneamino)ethane-1-ol]}, have been synthesized. The crystal structures of 1–3 were determined through single-crystal X-ray diffraction. The structure of mononuclear 1 shows a six-coordinate octahedral geometry around the manganese ion. Complex 2 is a five-coordinate tetranuclear copper complex with the central Cu atoms adopting distorted square pyramidal geometry. Complex 3 shows a trinuclear structure with the six-coordinate Mn ions surrounded by four L³ ligands and acetate ions. The in vitro cytotoxicity screening revealed that the 1–3 had substantial cytotoxicity against three cancer cell lines (HepG2, MDA-MB-231, and A549), even higher than that of cisplatin. Inspiringly, 2 derived from (R)-Schiff base ligand H₂L² was more potent against MDA-MB-231 cells. Interaction of 1–3 with calf-thymus DNA (CT-DNA) has been investigated using UV-vis, viscosity and thermal denaturation experiments. It was found that 1 binds with DNA through intercalation while 2 and 3 interact with DNA probably through groove-binding and electrostatic mode. In addition, the capability of the complexes to bind with bovine serum albumin was monitored using some spectral techniques. The metal ions, chiral and nuclearity have significant influences on the properties of the title compounds.     

Synthesis,characterization, DNA binding,cytotoxicity and molecular docking properties of three novel butterfly-like complexes with nitrogen-containing heterocyclic ligands

Three novel complexes, namely [Nd·L₁·HCOO·(H₂O)₄] ( 1 ), [Pr·L₁·HCOO·(H₂O)₄] ( 2 ) and [In·L₂·Cl·(H₂O)₂] ( 3 ) (L₁ = 1,1-bis(5-(pyrazin-2-yl)-1,2,4-triazol-3-yl)methane, L₂ = 1,1-bis(5-(pyrazin-2-yl)-1,2,4-triazol-3-yl)ketone), were synthesized and characterized. The molecular structures of 1 – 3 were confirmed using single-crystal X-ray diffraction. All three obtained complexes are zero-dimensional and connected to each other by hydrogen bonds. In 1 and 2 the metal is surrounded by nine donors and 3 has seven coordination sites. The interaction of 1 – 3 with calf thymus DNA (CT-DNA) was explored using UV absorption spectra and fluorescence spectra. The intrinsic binding constants of 1 – 3 with CT-DNA are about 1.9 × 10⁴, 1.4 × 10⁴ and 1.1 × 10⁴, respectively. Stern–Volmer quenching plots of 1 – 3 have slopes of 0.1508, 0.134 and 0.1205, respectively. The ability of these complexes to cleave pBR322 plasmid DNA was demonstrated using gel electrophoresis assay. Apoptosis studies of the three novel complexes showed a significant inhibitory effect on HeLa cells. Furthermore, MTT assays were used to evaluate the anticancer activity of the three complexes. The cytotoxicity study indicated that complex 1 possesses a higher inhibitory rate of HeLa cells than the other complexes. Especially, the efficacy of 1 was shown to be the highest for cisplatin at 24 h. A further molecular docking technique was introduced to understand the binding of the complexes toward the target DNA.     

Synthesis and in vitro biology of Co(II), Ni(II), Cu(II) and Zinc(II) complexes of functionalized beta-diketone bearing energy buried potential antibacterial and antiviral O,O pharmacophore sites

The clinically active functionalized β-diketones 1-(2′,4′-dihydroxyphenyl)-3-(2″-substitutedphenyl)-propane-1,3-dione (L₁)–(L₂) have been synthesized from Baker–Venkataraman transformation of 2,4-diaroyloxyacetophenones. Their transition metal complexes (1)–(8) have been prepared and characterized by physical, spectral and analytical data. The functionalized beta-diketone potentially acts as bidentate ligand and co-ordinate with the transition metal atom through beta-diketo system. The complexes have general formula [ML₂] where M = Co(II), Ni(II), Cu(II), Zinc(II) and L = ligand. The 1-(2′,4′-dihydroxyphenyl)-3-(2″-substitutedphenyl)-propane-1,3-dione and their transition metal complexes have been screened for in vitro antibacterial, antifungal and antioxidant bioassay. The biological activity data show that the transition metal complexes are more potent antibacterial, antifungal and antioxidant agents than the parent functionalized beta-diketone against different bacterial and fungal species. This constitutes a new group of compounds that can be used as potential metal derived drugs. Ultimately, here we can prompt about the use of metals for the drugs. The metal complexes were also studied for their thermogravimetric analyses.     

Synthesis, thermal stability, electronic features, and antimicrobial activity of phenolic azo dyes and their Ni(II) and Cu(II) complexes

Four water soluble azo dyes, 4-(isopropyl)-2-[(E)-(4-chlorophenyl)diazenyl]phenol (L ¹), 4-(isopropyl)-2-[(E)-(2,4-dichlorophenyl)diazenyl]phenol (L²), 4-(sec-butyl)-2-[(E)-(4-chlorophenyl) diazenyl]phenol (L ³), 4-(sec-butyl)-2-[(E)-(2,4-dichlorophenyl)diazenyl]phenol (L ⁴), and their Cu(II) and Ni(II) complexes were synthesized and characterized using spectroscopic methods. Examination of their thermal stability revealed similar decomposition temperature of approximately 260–300°C and that they were more thermally stable than their metal complexes. Ni(II) complexes of ligands L² and L⁴ were more stable than the other coordination compounds. Among the synthesized ligands, L² and the complexes Cu(L³)₂ and Ni(L⁴)₂ showed both antimicrobial and antifungal activity. However, the other ligands and the complexes were poorly active against selected microorganisms.     

DNA binding,cleavage, and cytotoxicity of binuclear phenolate nickel(II) complexes

Three binuclear phenolate complexes, [Ni₂(L¹)₂(OAc)](BPh₄)·DMF (1), [Ni₂(L²)₂(OAc)](BPh₄) (2), and [Ni₂(L³)₂(OAc)](OH)·3H₂O (3), where L¹ = 2-{[bis-(2-hydroxy-ethyl)-amino]-methyl}-4-methyl-phenol, L² = 2-{[bis-(2-hydroxy-ethyl)-amino]-methyl}-4-methoxy-phenol, and L³ = 2-{[bis-(2-hydroxy-ethyl)-amino]-methyl}-4-tert-butyl-phenol), have been synthesized. Single-crystal diffraction reveals that all the metal atoms are in a distorted octahedral geometry. The interactions of the complexes with calf thymus DNA (CT-DNA) have been investigated by UV–vis absorption, fluorescence emission, and circular dichroism spectroscopy and viscosity measurements. Furthermore, DNA cleavage mechanism shows that the complexes may be capable to promote DNA cleavage through oxidative DNA damage pathway, which is indicative of the involvement of hydroxyl radical, singlet oxygen, or singlet oxygen-like entity in the cleavage process. Cytotoxicity studies on the Hela and MCF-7 cancer cell lines show that complexes 1–3 exhibit excellent activity toward the tested tumor cell lines with respect to the standard drug carboplatin, revealing that they have the potential to act as effective metal-based anticancer drugs.     

Synthesis and characterization studies of 3-formyl chromone Schiff base complexes and their application as antitumor,antioxidant and antimicrobial

A novel Schiff base namely (E)-3-((2,6-dihydroxypyrimidin-4-ylimino)methyl)-4H-chromen-4-one and its Co (II), N (II)i, Cu (II) and Cd (II) complexes have been synthesized and proved by elemental analysis, molar conductance, thermal analysis (TGA), Inductive Coupled plasma (ICP), magnetic moment measurements, X-ray powder diffraction, IR, EI-mass,¹H NMR, ¹³C NMR,UV–Vis. and ESR spectral studies. On the basis of these data, it is evident that the Schiff base acts as bidentate via oxygen atom of carbonyl group and azomethine nitrogen atom for Co (II) complex; monobasic bidentate ligand for Ni (II), Cu (II) and Cd (II) complexes via oxygen atom of hydroxyl group and nitrogen atom of pyrimidine ring. The results showed all complexes have octahedral geometry. The average particle size of the ligand and its complexes were found to be 1.010–0.343 nm. The pharmacological action (antioxidant, antimicrobial and anticancer) of the prepared compounds is studied. The antitumor activity of the ligand and its metal complexes is evaluated against human liver carcinoma (HEPG2) cell. The data displayed the Co (II) complexes strong cytotoxicity where IC₅₀ values of Co (II) complex and 5-fluorouracil (stander drug) are 9.33 and 7.86 μg/ml respectively. The Co (II) and Cd (II) complexes have antibacterial activity more than ampicillin (stander drug). The interaction of the synthesized compounds with calf-thymus DNA (CT-DNA) has been performed via absorption spectra and viscosity technique. The DNA- binding constants have been determined.     

In-vitro antibacterial activity of Ni(II), Cu(II), and Zn(II) complexes incorporating new azo-azomethine ligand possessing excellent antioxidant,anti-inflammatory activity and protective effect of free radicals against plasmid DNA

Azo Schiff base ligand 2-hydroxy-3-methoxy-5-(tolyldiazenyl)benzaldehyde oxime (HL¹) and 2-hydroxy-3-methoxy-5-(methoxyphenyl)benzaldehyde oxime (HL²) were prepared along with their transition metal complexes of Ni(II), Cu(II), and Zn(II). Ligands and their metal complexes were characterized by several analysis techniques. In- vitro antibacterial, antioxidant and anti-inflammatory activities of synthesized ligands and their metal complexes have been studied. Biological study showed that amongst all the synthesized compounds, Cu(II) complexes possessed excellent antibacterial activity than standard antibiotic Chloramphenicol. Ligands (HL¹) and (HL²) showed excellent antioxidant as well as anti-inflammatory activity. Both the ligands were tested for their protective effect of free radicals against plasmid DNA and it was found that both the ligands showed good DNA nicking activity.     

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 (L^a and L^b) were prepared from the condensation of quinoline 2‐aldehyde with 2‐aminopyridine (ligand L^a) and from the condensation of oxamide with furfural (ligand L^b). Mixed ligand complexes of the type M⁺²L^a/b L^c were prepared, where (L^a and L^b) the primary ligands and L^c was 2,6‐pyridinedicarboxylic acid as secondary ligand. Metal ions used were Fe(II), Co(II), Ni(II) and Zn(II) for mixed ligands L^a L^c and Fe(II), Co(II), Ni(II), Cu(II), Hg(II) and Zn(II) for L^bL^c mixed ligands. L^a and L^b Schiff base ligands were both characterized using elemental analyses, molar conductance, IR, ¹H and ¹³C NMR. Mass spectra for L^b, [Zn(L^a)L^cCl]Cl and [Cu(L^b)L^cCl]Cl were also studied. ESR spectrum of the [Cu(L^b) L^cCl]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 L^a and L^b ligands behaved as neutral bidentate ligands with N₂ donation sites (quinoline N and azomethine N for L^a and two azomethine N for L^b). 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 L^a, L^b 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.     

Synthesis,Characterization, Crystal Structure,and Biological Activities of Transition Metal Complexes with 1‐Phenyl‐3‐methyl‐5‐hydroxypyrazole‐4‐methylene‐8′‐quinolineimine

The Schiff base ligand, 1‐phenyl‐3‐methyl‐5‐hydroxypyrazole‐4‐methylene‐8′‐quinolineimine, and its Cu^II, Zn^II, and Ni^II complexes were synthesized and characterized. The crystal structure of the Zn^II complex was determined by single‐crystal X‐ray diffraction, indicating that the metal ions and Schiff base ligand can form mononuclear six‐coordination complexes with 1:1 metal‐to‐ligand stoichiometry at the metal ions as centers. The binding mechanism and affinity of the ligand and its metal complexes to calf thymus DNA (CT DNA) were investigated by UV/Vis spectroscopy, fluorescence titration spectroscopy, EB displacement experiments, and viscosity measurements, indicating that the free ligand and its metal complexes can bind to DNA via an intercalation mode with the binding constants at the order of magnitude of 105–106 M ^–1, and the metal complexes can bind to DNA more strongly than the free ligand alone. In addition, antioxidant activities of the ligand and its metal complexes were investigated through scavenging effects for hydroxyl radical in vitro, indicating that the compounds show stronger antioxidant activities than some standard antioxidants, such as mannitol. The ligand and its metal complexes were subjected to cytotoxic tests, and experimental results indicated that the metal complexes show significant cytotoxic activity against lung cancer A 549 cells.     

Preparation,characterization of some transition metal complexes of hydrazone derivatives and their antibacterial and antioxidant activities

A new series of metal complexes of Pd(II), Cd(II) and Cu(II, I) of polydentate Schiff base ligand (H₂L), namely ((Z)-2-(phenylamino)-N'-(thiophen-2-ylmethylene) acetohydrazide) have been prepared. The ligand and its metal complexes have been characterized based on various physicochemical studies as elemental analyses, molar conductance, spectral (UV–Vis, MS, IR, ¹H NMR, ¹³C NMR and XRD), magnetic moment measurements and thermal studies (TG, DTG). In the view of previous studies, the ligand (H₂L) acts as polydentate one and coordinates with metal ions to form all metal complexes. The kinetic and thermodynamic parameters of decomposition process (ΔG, ΔH, ΔS) were calculated. The possible structures of the metal complexes have been computed using the molecular mechanic calculations using the hyper chem. 8.03 molecular modeling program. The calculations are performed to obtain the optimized molecular geometry. The antibacterial study of the selected compounds was assayed against two pathogenic bacteria. Moreover, the complexes (Cu II, I), Cd(II), Pd(II)) and the ligand revealed excellent antioxidant properties and could be useful in fighting the free radicals which occur in close connection with cancerous cells. It was remarkable that the two complexes (Cu II, I) demonstrated stronger antioxidant effects than their parent compounds. It is clear that the new complexes are good active compounds for use in a variety of applications.     

Synthesis,characterization and α‐amylase and α‐glucosidase inhibition studies of novel vanadyl chalcone complexes

A series of chalcone ligands and their corresponding vanadyl complexes of composition [VO (L^I–IV)₂(H₂O)₂]SO₄ (where L^I = 1,3‐Diphenylprop‐2‐en‐1‐one, L^II = 3‐(2‐Hydroxy‐phenyl)‐1‐phenyl‐propenone, L^III = 3‐(3‐Nitro‐phenyl)‐1‐phenyl‐propenone, L^IV = 3‐(4‐Methoxy‐phenyl)‐1‐phenyl‐propenone) have been synthesized and characterized using various spectroscopic (Fourier‐transform infrared, electrospray ionization mass, nuclear magnetic resonance, electron paramagnetic resonance, thermogravimetric analysis, vibrating sample magnetometer) and physico‐analytic techniques. Antidiabetic activities of synthesized complexes along with chalcones were evaluated by performing in vitro and in silico α‐amylase and α‐glucosidase inhibition studies. The obtained results displayed moderate to significant inhibition activity against both the enzymes by vanadyl chalcone complexes. The most potent complexes were further investigated for the enzyme kinetic studies and displayed the mixed inhibition for both the enzymes. Further, antioxidant activity of vanadyl chalcone complexes was evaluated for their efficiency to release oxidative stress using 2,2‐diphenyl‐1‐picryl‐hydrazyl‐hydrate assay, and two complexes (Complexes 2 and 4 ) have demonstrated remarkable antioxidant activity. All the complexes were found to possess promising antidiabetic and antioxidant potential.     

Synthesis,spectral characterization,theoretical, antimicrobial,DNA interaction and in vitro anticancer studies of Cu(II) and Zn(II) complexes with pyrimidine-morpholine based Schiff base ligand

Novel Cu(II) (1) and Zn(II) (2) complexes with 4-(1-(4-morpholinophenyl)ethylideneamino)pyrimidine-5-carbonitrile) (L) have been synthesized and characterized by various spectroscopic and analytical techniques. DFT (density functional theory) studies result confirms that, LMCT mechanism have been done between L and M(II) ions. The antimicrobial studies indicate that the ligand L and complexes 1 & 2 exhibit higher activity against the E. coli bacteria and C. albicans fungi. The groove binding mode of ligand L and complexes 1 & 2 with CT-DNA have been confirmed by electronic absorption, competitive binding, viscometric and cyclic voltammetric studies. The electronic absorption titration of ligand L and complexes 1 & 2 with DNA have been carried out in different buffer solutions (pH 4.0, 7.0 & 10.0). The K_b values of ligand L and complexes 1 & 2 are higher in acidic buffer at pH 4.0 (K_b = 2.42 × 10⁵, L; 2.8 × 10⁵, 1; 2.65 × 10⁵, 2) and the results revealed that, the interaction of synthesized compounds with DNA were higher in the acidic medium than basic and neutral medium. Furthermore, CT-DNA cleavage studies of ligand L and complexes 1 & 2 have been studied. The in vitro anticancer activities results show that complexes 1 & 2 have moderate cytotoxicity against cancer cell lines and low toxicity on normal cell line than ligand L.     

Synthesis,structure, and DNA binding of three reduced amino-acid Schiff-base zinc(II), nickel(II), and cadmium(II) complexes

Three new reduced amino-acid Schiff-base complexes, [Zn(HL)₂] · H₂O (1), [Ni(HL)₂] · H₂O (2), and [Cd(HL)₂] · H₂O (3), where H₂L is a reduced Schiff base derived from condensation of N-(2-hydroxybenzaldehyde) and L-histidine, have been synthesized and characterized by elemental analysis, UV-Vis absorption spectra and single crystal X-ray diffraction. Complexes 1–3 are isostructural. All metal centers are six-coordinate with O₂N₄ donor sets in slightly distorted octahedra. Unlike its Schiff-base counterpart, the deprotonated monoanionic ligand HL^? has a more flexible backbone and two HL^? are tridentate to one metal. Moreover, the binding interactions of these complexes with calf thymus DNA (CT-DNA) have been investigated by UV-Vis spectra and fluorescence quenching, which show that the complexes bind in an intercalative mode.     

Synthesis,characterization and antioxidant,antibacterial activity Zn2+, Cu2+, Ni2+ and Co2+, complexes of ligand [2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzo[d]imidazole]

New metal complexes of (Zn(II), Co(II), Ni(II) and Cu(II)) based on the ligand 2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzo[d]imidazole] were synthesized, whose structures were determined with the different spectroscopic techniques ¹H NMR,¹³C NMR, FT-IR, UV–Visible and by mass spectrometry. The thermal analysis was performed by TG-DTA. The antioxidant activity of the ligand and its complexes was evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl) method, in comparison with the synthetic antioxidant, ascorbic acid. The results obtained showed that the antioxidant activity of the ligand and its complexes is moderate and that the copper complex has a high activity that exceeds that of ascorbic acid. Antimicrobial activity of the ligand and its metal complexes was studied against two Gram-positive bacteria: Bacillus subtilis ILP1428B, Staphylococcus aureus CIP543154 and two Gram-negative bacteria: Pseudomonas aeruginosa ATCC27653, Escherichia coli CIP5412 (American Type Culture Collection)the activity data show that the metal complexes are more potent than the free ligand.     

Ligational behavior of thiosemicarbazone,semicarbazone and thiocarbohydrazone ligands towards VO(IV), Ce(III), Th(IV) and UO2(VI) ions: Synthesis,structural characterization and biological studies

Mono- and binuclear VO(IV), Ce(III), Th(IV) and UO₂(VI) complexes of thiosemicarbazone, semicarbazone and thiocarbohydrazone ligands derived from 4,6-diacetylresorcinol were synthesized. The structures of these complexes were elucidated by elemental analyses, IR, UV–vis, ESR, ¹H NMR and mass spectra as well as conductivity and magnetic susceptibility measurements and thermal analyses. The thiosemicarbazone (H₄L¹) and the semicarbazone (H₄L²) ligands behave as dibasic pentadentate ligands in case of VO(IV) and UO₂(VI) complexes, tribasic pentadentate in case of Ce(III) complexes and monobasic pentadentate in case of Th(IV) complexes. However, the thiocarbohydrazone ligand (H₃L³) acts as a monobasic tridentate ligand in all complexes except the VO(IV) complex in which it acts as a dibasic tridentate ligand. The antibacterial and antifungal activities were also tested against Rhizobium bacteria and Fusarium-Oxysporium fungus. The metal complexes of H₄L¹ ligand showed a higher antibacterial effect than the free ligand while the other ligands (H₄L² and H₃L³) showed a higher effect than their metal complexes. The antifungal effect of all metal complexes is lower than the free ligands.     

Synthesis,physico-chemical and antimicrobial screening studies of some transition metal complexes with O:O donor ligands

The solid complexes of Mn^II, Fe^III, Co^II, Ni^II and Cu^II with 3-(3-furan-2yl-acryloyl)-6-methyl-pyran-2,4-dione(L¹) and 3-(3-thiophene-2yl-acryloyl)-6-methyl-pyran-2,4-dione (L²) have been synthesized and characterized by elemental analysis, conductometry, thermal analysis, magnetic, i.r., P-n.m.r., u.v.–vis, X-ray diffraction and antimicrobial study. From the analytical and spectral data, the stoichiometry of the complexes has been found to be 1:2 (metal:ligand). I.r. spectral data suggest that the ligand behaves as a dibasic bidentate ligand with O:O donor sequence towards metal ions. The physico-chemical data suggests distorted octahedral geometry for Cu^II complexes and octahedral geometry for all other complexes. The X-ray diffraction suggests an Orthorhombic crystal system for the Cu^II complex and Monoclinic crystal system for Co^II and Ni^II complexes of ligand L¹. The ligands and their metal complexes were screened for antibacterial activity against Staphylococcus aureus and Escherichia coli, and the fungicidal activity against Aspergillus flavus, Curvularia lunata and Penicillium notatum.     

Synthesis,characterization, and biological activities of macrocyclic polyamine complexes

Two new dinuclear macrocyclic complexes, [Ni₂L¹(OAc)]·ClO₄ (1) and [Co₂L²(OAc)]·1.5(ClO₄)·0.5Na·2(CH₃OH) (2) (where H₂L¹ and H₂L² are the condensation products of N,N-bis(3-aminopropyl)-4-methoxybenzylamine with 2,6-diformyl-4-brominephenol and 2,6-diformyl-4-methylphenol in the presence of metal ions, respectively) have been synthesized and characterized by infrared spectra, elemental analysis, electrospray mass spectra, and X-ray single crystal diffraction. The interactions of the complexes with CT-DNA have been measured by UV-absorption titrations and fluorescence quenching experiments.     

Synthesis,characterization, catalytic,antimicrobial, DNA binding and cleavage studies of N-functionalized tetraazamacrocyclic binuclear copper(II) complexes

A series of binuclear copper(II) complexes of N-functionalized cyclam derivatives has been prepared by the Schiff base condensation of 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC-a), 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC-b) with appropriate aliphatic diamines, and copper(II) perchlorate. All the complexes were characterized by elemental, FT-IR, UV–Vis, ESI and ESR spectral analysis. The room temperature magnetic moment studies depicts the presence of an antiferromagnetic interaction in the binuclear complexes, which is also observed from the broad ESR spectra with a g value of 2.10–2.11. Variable-temperature magnetic susceptibility study of the complex [Cu₂L^2a](ClO₄)₂ shows that the calculated ?2J value is 219 cm^?1, which conveys a spin–spin interaction between the two copper(II) ions. The catechol oxidation and hydrolysis of 4-nitrophenylphosphate were carried out by using the complexes as a catalyst. All the above metal complexes were screened for antimicrobial and human pathogenic fungal activity. The binding of the complexes to calf thymus DNA (CT-DNA) has been investigated with UV–Vis and fluorescence spectroscopy. All complexes display significant cleavage property of circular plasmid pBR322 DNA into linear form. Spectral, electrochemical, magnetic and catalytic studies support the distortion of the copper ion geometry that arises as the macrocyclic ring size increases.