A. Sakthivel

Transition metal complexes with Schiff-base ligands: 4-aminoantipyrine based derivatives–a review

The survey highlights structural properties and biological studies of transition metal complexes derived from 4-aminoantipyrine. The most important results of extensive studies (syntheses, spectral, magnetic, redox, structural characteristics, antimicrobial and DNA cleavage) of the metal complexes with heterocyclic Schiff bases of 4-aminoantipyrine with some aldehydes and oximes are reviewed.

Novel metal-based pharmacologically dynamic agents of transition metal(II) complexes: Designing, synthesis, structural elucidation, DNA binding and photo-induced DNA cleavage activity

Novel Schiff base Cu(II), Ni(II), Co(II) and Zn(II) complexes have been designed and synthesized using the macrocyclic ligand derived from the condensation of diethylphthalate with Schiff base, obtained from benzene-1,2-diamine and 3-benzylidene-pentane-2,4-dione. The ligand and its complexes have been characterized by analytical and spectral techniques. DNA binding properties of these complexes have been investigated by UV-vis, viscosity measurements, cyclic voltammetric and differential pulse voltammogram studies. The intrinsic binding constants for Co(II), Ni(II), Cu(II) and Zn(II) complexes are 1.6x10(6), 1.8x10(6), 2.0x10(6) and 1.5x10(6) M(-1) respectively which are obtained from electronic absorption experiment. Control DNA cleavage experiments using pUC19 supercoiled (SC) DNA and minor groove binder (distamycin) suggest the major groove binding tendency for the synthesized complexes. In the presence of a reducing agent like 3-mercaptopropionic acid (MPA), the synthesized complexes show chemical nuclease activity under dark reaction condition. The complexes also show efficient photo-induced DNA cleavage activity on irradiation with a monochromatic UV light of 360 nm in the presence of inhibitors. Control experiments show inhibition of cleavage in the presence of singlet oxygen quencher like sodium azide and enhancement of cleavage in D(2)O, suggesting the formation of singlet oxygen as a reactive species in a type-II process.

Design, structural elucidation, DNA interaction and antimicrobial activities of metal complexes containing tetraazamacrocyclic Schiff bases

Tetraazamacrocyclic Schiff bases, designed and synthesized from 3-hydroxy-4-nitrobenzylideneacetoacetanilide/3-hydroxy-4-nitrobenzylidene-o-acetoacetotoluidide and 1,2-diaminobenzene, are tetradentate ligands and form solid cationic complexes with CuII, NiII, CoII, ZnII, MnII, and VOIV salts in ethanol. Microanalytical data, magnetic moment, electronic, IR, Mass, 13C NMR, IH NMR, and electron spin resonance (ESR) techniques were used to characterize the synthesized compounds. Electronic absorption and IR spectra suggest that all the complexes are square planar, while the oxovanadium complexes are square pyramidal. Elemental analyses and mass spectra suggest that the general formula of the complexes is [ML]X (where L = L1 or L2, X = 2Cl− or ). Electrolytic behavior of the chelates was assessed from conductance data. The X-band ESR spectra of copper and oxovanadium complexes, recorded in dimethyl sulfoxide at 300 and 77 K, are discussed. Binding of the metal complexes with DNA has been investigated by spectroscopic, viscometric, and voltammetric methods. These data suggest that the complexes interact with DNA by intercalative binding. A comparative study of minimum inhibitory concentration values of the ligands and their complexes indicates that the complexes exhibit higher antimicrobial activity than the free ligands. The nuclease activity shows that the copper, manganese, nickel, and vanadium complexes cleave DNA through redox chemistry.

Binuclear copper and zinc complexes possessing bio-potential ligands: synthesis, characterization, antimicrobial, SOD mimetic, DNA binding, and cleavage studies

Schiff bases (L) viz, N,N′,N′′,N′′′-tetra-3,4-dimethoxybenzalidene-3,3′-diaminobenzidine (TDBD), N,N′,N′′,N′′′-tetra-4-hydroxy-3-methoxybenzalidene-3,3′-diaminobenzidine (THMBD), and N,N′,N′′,N′′′-tetra-3-hydroxy-4-nitrobenzalidene-3,3′-diaminobenzidine (THNBD) afford binuclear [M2LCl4] complexes where M = Cu(II) or Zn(II). These Schiff bases and their binuclear complexes have been characterized by analytical and spectral data showing square-planar geometry on metalation with Cu2+. Intercalative binding of these complexes with DNA has been investigated by electronic absorption spectroscopy, viscosity measurements, cyclic voltammetry, and differential pulse voltammetry. Control DNA cleavage experiments using pUC19 supercoiled (SC) DNA and minor groove binder distamycin suggest that these synthesized complexes bind to the major groove. In the presence of a reducing agent like 3-mercaptopropionic acid (MPA), they show chemical nuclease activity. They also show an efficient photo-induced DNA cleavage on irradiation with a monochromatic UV light of 360 nm in the presence of inhibitors. Control experiments indicate the inhibition of cleavage in the presence of singlet oxygen quencher like sodium azide and the enhancement of cleavage in D2O show the formation of singlet oxygen as reactive species. The superoxide dismutase (SOD)-mimetic activity of the synthesized complexes has been assessed for their ability to inhibit the reduction of nitroblue tetrazolium chloride (NBT). The complexes have promising SOD-mimetic activity. The antimicrobial results indicate that the complexes inhibit the growth of bacteria and fungi more than free ligands.

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.

Exploring DNA binding and nucleolytic activity of few 4-aminoantipyrine based amino acid Schiff base complexes: A comparative approach

A series of novel Co(II), Cu(II), Ni(II) and Zn(II) complexes were synthesized from Schiff base(s), obtained by the condensation of 4-aminoantipyrine with furfural and amino acid (glycine(L1)/alanine(L2)/valine(L3)) and respective metal(II) chloride. Their structural features and other properties were explored from the analytical and spectral methods. The binding behaviors of the complexes to calf thymus DNA were investigated by absorption spectra, viscosity measurements and cyclic voltammetry. The intrinsic binding constants for the above synthesized complexes are found to be in the order of 10(2) to 10(5) indicating that most of the synthesized complexes are good intercalators. The binding constant values (Kb) clearly indicate that valine Schiff-base complexes have more intercalating ability than alanine and glycine Schiff-base complexes. The results indicate that the complexes bind to DNA through intercalation and act as efficient cleaving agents. The in vitro antibacterial and antifungal assay indicates that these complexes are good antimicrobial agents against various pathogens. The IC50 values of [Ni(L1)2] and [Zn(L1)2] complexes imply that these complexes have preferable ability to scavenge hydroxyl radical.

Synthesis, characterization, DNA binding, photo-induced DNA cleavage, and antimicrobial activity of metal complexes of a Schiff base derived from bis(3-aminophenyl)malonamide

The peptide linkage Schiff base (H2L) and its complexes have been synthesized and fully characterized by elemental analysis, UV–Vis, FTIR, 1H-NMR, 13C-NMR, EPR, and FAB-mass spectra. The stoichiometry of the complexes is [ML] (where M = Cu(II), Co(II), Ni(II), Zn(II), and VO(IV)). All the complexes exhibit square-planar geometry except the vanadyl complex which has square-pyramidal geometry. Interactions of the complexes and free ligand with double-stranded calf thymus DNA (CT-DNA) are studied by UV-spectrophotometric, electrochemical, and viscosity measurements. The data suggest that all the complexes form adducts with DNA and distort the double helix by changing the base stacking. Vanadyl complex forms a weaker adduct to CT-DNA than other complexes, probably due to the square-pyramidal geometry. CT-DNA induces extensive distortion in the planarity of vanadyl complex as EPR spectral calculations reveal. The intrinsic binding constants (K b) of [ZnL], [CuL], [CoL], and [NiL] are 1.1 × 105, 1.4 × 105, 0.8 × 105, and 0.6 × 105 M−1, respectively. Photo-induced DNA cleavage indicates that all complexes cleave DNA effectively. Control DNA cleavage experiments using pUC19 supercoiled (SC) DNA and minor groove binder distamycin suggest major groove binding for the synthesized complexes. The antimicrobial results indicate that the complexes inhibit the growth of bacteria and fungi more than the free ligand.

Synthesis, structural characterization, antimicrobial, DNA-binding, and photo-induced DNA cleavage activity of some bio-sensitive Schiff base copper(II) complexes

Schiff base mixed-ligand copper complexes [CuL1(phen)Cl2], [CuL1(bipy)Cl2], [Cu(L1)2Cl2], [Cu(L2)2Cl2], [CuL2(bipy)Cl2], and [CuL2(phen)Cl2] (where L1 = 4-[3,4-dimethoxy-benzylidene]-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazole-3-one; L2 = 4-[3-hydroxy-4-nitro-benzylidene]-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazole-3-one; phen = 1,10-phenanthroline; and bipy = 2,2′-bipyridine) have been synthesized and characterized. Their DNA-binding properties have been studied by electronic absorption spectra, viscosity, and electrochemical measurements. The absorption spectral and viscosity results suggest that the copper(II) complexes bind to DNA via partial intercalation. The addition of DNA resulting in the decrease of the peak current of the copper(II) complexes indicates their interaction. Interaction between the complexes and DNA has also been investigated by submarine gel electrophoresis. The copper complexes cleave supercoiled pUC19 DNA to nicked and linear forms through hydroxyl radical and singlet oxygen in the presence of 3-mercaptopropionic acid as the reducing agent. These copper complexes promote the photocleavage of pUC19 DNA under irradiation at 360 nm. Mechanistic study reveals that singlet oxygen is likely to be the reactive species responsible for the cleavage of plasmid DNA by the synthesized complexes. The in vitro antimicrobial study indicates that the metal chelates have higher activity against the bacterial and fungal strains than the free ligands.

TEMPLATE SYNTHESIS OF NOVEL 14-MEMBERED TETRAAZAMACROCYCLIC TRANSITION METAL COMPLEXES: DNA CLEAVAGE AND ANTIMICROBIAL STUDIES

ABSTRACT A new series of 14 membered tetraazamacrocyclic complexes of type [ML]X 2 , where M=Ni(II), Co(II), Cu(II), Zn(II), Hg(II), VO(IV), Cd(II) and Mn(II); X 2 = 2Cl - ; SO 42- , have been synthesized by incorporating an N 4 donor site via. the template condensation of o-phenylenediamine, formaldehyde, p-anisidine and metal salt. The structural features of the complexes have been confirmed by spectral and analytical data. From the data, a square-planar geometry around the central metal ion has been suggested except VO(IV) complex which has square-pyramidal geometry. The antimicrobial screening data show good results. From the nuclease activity of the above metal complexes, it is inferred that only the copper and nickel complexes cleave DNA through redox chemistry.Key words: o-phenylenediamine, p-anisidine, CT DNA, antimicrobial activity, nuclease activity INTRODUCTION Tetraaza metal complexes are considered to be models for metalloporphyrins and metallocorrins due to their intrinsic structural properties. The uses of macrocyclic metal complexes as bioinorganic models have able portrayed in many reviews such as that of Vogt et al

SYNTHESIS, STRUCTURAL CHARACTERIZATION AND ANTIMICROBIAL STUDIES OF NOVEL SCHIFF BASE COPPER(II) COMPLEXES

ABSTRACT Five novel copper(II) complexes have been synthesized using Schiff base ligands, synthesized by the condensation reaction of anthranilic acid and Knoevenagel b-ketoanilide condensates (obtained by the condensation of acetoacetanilide and substituted benzaldehydes). The ligands and copper(II) complexes have been characterized on the basis of Microanalytical, Mass, UV-Vis., IR, 1 H NMR, ESR, XRD and CV spectral studies, as well as magnetic susceptibility and conductivity data. On the basis of spectral studies, a square-planar geometry has been proposed for the copper(II) complexes. From the XRD data, the CuL 1 complex has the crystallite size of 50 nm respectively. The in vitro antimicrobial activity of the compounds is tested against the bacteria Escherichia coli, Salmonella typhi, Staphylococcus aureus, Klebsiella pneumoniae and Pseudonomas aeruginosa and fungi Aspergillus niger , Rhizopus stolonifer , Aspergillus flavus, Rhizoctonia bataicola and Candida albicans by well diffusion method. The complexes show stronger antimicrobial activity than the free ligands. They represent a novel class of metal-based antimicrobial agents which provide opportunities for a large number of synthetic variations for modulation of the activities.