DNA binding, photoactivated DNA cleavage and cytotoxic activity of Cu(II) and Co(II) based Schiff-base azo photosensitizers.

A new class of Cu(II) and Co(II) complexes of azo-containing Schiff base of the type [Cu(L1)2] and [Co(L1)2], where L1=4-[(E)-{2-hydroxy-3-[(E)-(4-bromophenyl)diazenyl]benzylidene}amino]benzoic acid have been synthesized and characterized. Extension of conjugation and the presence of free carboxylic acid group of the ligand L1 increased the wavelength of the complexes from visible region to the near IR region (620-850 nm). The Cu(II) and Co(II) complexes interacted with CT-DNA via intercalative mode with the respective Kb value of 3.2×10(4) M(-1) and 2.9×10(4) M(-1) and acted as proficient photocleavers of SC pUC19 DNA in UV-A light, forming (1)O2 as the reactive oxygen species with the quantum yield of 0.38 and 0.36, respectively. Furthermore, the Cu(II) and Co(II) complexes showed photocytotoxicity toward two selected tumor cell lines MCF-7 and A549 by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) method, and the Cu(II) complex exhibits higher photocytotoxicity than Co(II) complex against each of the selected cell lines, this result is identical with their DNA binding ability order.

Luminescence properties of blue-red emitting multilayer coated single structure ZnS/MnS/ZnS nanocomposites.

Uncoated ZnS, MnS and ZnS/MnS/ZnS nanocomposites were successfully synthesized by chemical co-precipitation method in air atmosphere by varying the thicknesses of MnS layer. Characterization techniques such as X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), UV-visible absorption and photoluminescence (PL) spectroscopy were used to characterize the novel ZnS/MnS/ZnS nanocomposites. The obtained particles were highly crystalline and monodispersed with an average particles size of 4.5-6.5 nm. The room temperature photoluminescence (PL) study of ZnS/MnS/ZnS nanocomposites showed an enhanced intensity with different concentration of manganese acetate. The presences of MnS layer in the nanocomposite have tuned the PL emission in the IR region. Addition of manganese acetate (0.1-0.4 M) in the nanocomposite showed a distinct PL emission peak centered at 740 nm i.e. in the red region with significant red shift. The PL emission of ZnS and MnS were tuned in the nonvisible IR region. It is shown that the variation in thickness of MnS layer leads to an enhanced photoluminescence intensity/efficiency of ZnS/MnS/ZnS nanocomposites.

Metal based photosensitizers of tetradentate Schiff base: promising role in anti-tumor activity through singlet oxygen generation mechanism.

In the present investigation, a Schiff base N'(1),N'(3)-bis[(Z)-(2-hydroxynapthyl)methylidene]benzene-1,3-dicarbodihydrazide (L1) and its Co(II), Ni(II) and Cu(II) complexes have been synthesized and characterized as novel photosensitizing agents for photodynamic therapy (PDT). The interaction of these complexes with calf thymus DNA (CT DNA) has been explored using absorption, thermal denaturation and viscometric studies. The experimental results revealed that Co(II) and Ni(II) complexes on binding to CT DNA imply a covalent mode, most possibly involving guanine N7 nitrogen of DNA, with an intrinsic binding constant Kb of 4.5×10(4)M(-1) and 4.2×10(4)M(-1), respectively. However, interestingly, the Cu(II) complex is involved in the surface binding to minor groove via phosphate backbone of DNA double helix with an intrinsic binding constant Kb of 5.7×10(4)M(-1). The Co(II), Ni(II) and Cu(II) complexes are active in cleaving supercoiled (SC) pUC19 DNA on photoexposure to UV-visible light of 365nm, through (1)O2 generation with quantum yields of 0.28, 0.25 and 0.30, respectively. Further, these complexes are cytotoxic in A549 lung cancer cells, showing an enhancement of cytotoxicity upon light irradiation.

Synthesis, DNA-binding, DNA-photonuclease profiling and antimicrobial activity of novel tetra-aza macrocyclic Ni(II), Co(II) and Cu(II) complexes constrained by thiadiazole.

A new tetra-aza macrocyclic ligand, L (C(24)H(16)N(12)O(2)S(4)) and its complexes of type, [MLCl(2)] and [CuL]Cl(2) (where M=Ni(II), Co(II); L=N,N'-(benzene-1,3-diyldi-1,3,4-thiadiazole-5,2-diyl)bis{2-[(5-benzene-1,3-diyl-1,3,4-thiadiazol-2-yl)amino]acetamide}) were synthesized and characterized by the spectral and analytical techniques. An octahedral geometry has been proposed for Ni(II) and Co(II) complexes while Cu(II) complex exhibit a square planar geometry. All the synthesized metal complexes were screened for their in vitro antimicrobial activity against selected species of pathogenic bacteria and fungi. The binding property of the complexes with CT-DNA was studied by absorption spectral analysis, followed by viscosity measurement and thermal denaturation studies. The photo induced cleavage studies revealed that the complexes possess photonuclease property against pUC19 DNA under UV-visible irradiation.

Synthesis, DNA binding and cleavage studies of Ni(II) complexes with fused aromatic N-containing ligands.

The three Ni(II) complexes of fused aromatic N-containing ligands such as [Ni(bnp)(3)](PF(6))(2) (1), [Ni(phen)(2)(bnp)](PF(6))(2) (2) and [Ni(bpy)(2)(bnp)](PF(6))(2) (3) (where bnp=dibenzo(b)1,8-naphthpyridine, phen=1,10-phenanthroline and bpy=bipyridine) were synthesized and structurally characterized. Elemental analysis, magnetic and spectroscopic data suggested octahedral geometry for all the complexes. Binding of these complexes with (ds)DNA were analyzed by absorption spectra, viscosity and thermal denaturation studies. Detailed analysis revealed that the metal complexes intercalates into the DNA base stack as intercalator. The oxidative cleavage activities of the complexes were studied with supercoiled (SC)pUC19 DNA by using gel electrophoresis, and the results show that complexes have potent nuclease activity.

Binding and oxidative cleavage studies of DNA by mixed ligand Co(III) and Ni(II) complexes of quinolo [3,2-b]benzodiazapine and 1,10-phenanthroline.

Two mixed ligand complexes of the type [M(phen)(2)(qbdp)](PF(6))n.xH(2)O where M = Co(III) and Ni(II), qbdp = quinolo[3,2-b] benzodiazepine and phen = 1,10-phenanthroline, n = 3 or 2, x = 2 or 3 have been synthesized and characterized by employing analytical and spectral methods. The DNA binding property of the complexes with calf thymus-DNA has been investigated by using absorption spectra, viscosity measurements as well as thermal denaturation studies. The absorption spectral results indicate that the Co(III) and Ni(II) complexes intercalate between the base pairs of the DNA tightly with intrinsic DNA binding constant of 6.4 x 10(4) and 4.8 x 10(4) M(-1) in Tris HCl buffer containing 50 mM NaCl, respectively. The large enhancement in the relative viscosity of DNA on binding to the quinolo [3,2-b] benzodiazepine supports the proposed DNA binding modes. The complexes on reaction with super coiled (SC) DNA shows nuclease activity.

Co(III) and Ni(II) complexes containing bioactive ligands: synthesis, DNA binding, and photocleavage studies.

DNA binding and photocleavage characteristics of a series of mixed ligand complexes of the type [M(bpy)(2)qbdp](PF(6))(n).xH(2)O (where M = Co(III) or Ni(II), bpy = 2.2'-bipryidine, qbdp = Quinolino[3,2-b]benzodiazepine, n = 3 or 2 and x = 5 or 2) have been investigated. The DNA binding property of the complexes with calf thymus DNA has been investigated by using absorption spectra, viscosity measurements, as well as thermal denaturation studies. Intrinsic binding constant (K(b)) has been estimated under similar set of experimental conditions. Absorption spectral studies indicate that the Co(III) and Ni(II) complexes intercalate between the base pairs of the CT-DNA tightly with intrinsic DNA binding constant of 1.3 x 10(6) and 3.1 x 10(5) M(-1) in Tris-HCl buffer containing 50 mM NaCl, respectively. The proposed DNA binding mode supports the large enhancement in the relative viscosity of DNA on binding to quinolo[3,2-b]benzodiazepine. The oxidative as well as photo-induced cleavage reactions were monitered by gel electrophoresis for both complexes. The photocleavage experiments showed that the cobalt(III) complex can cleave pUC19 DNA effectively in the absence of external additives as an effective inorganic nuclease.