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Metal-based photosensitizers of the type [Co(L)Cl2] (1), [Ni(L)Cl2] (2) and [Cu(L)]Cl2 (3), where L = N′1,N′3-bis[(E)-thiophen-2-ylmethylidene]benzene-1,3-dicarbohydrazide have been synthesized and characterized by advanced spectroscopic and analytical techniques. The interactions of the complexes with CT DNA were investigated by viscosity analysis, thermal denaturation and absorption spectroscopic techniques. Absorption spectral (Kb = 5.57 × 104 M−1 (1), 4.45 × 104 M−1 (2), 2.8 × 104 M−1 (3)), thermal denaturation and viscosity measurements reveal that 1, 2 and 3 interact with DNA through intercalation. The complexes are photocleavers of SC pUC19 DNA in UV-A light forming 1O2 as the reactive oxygen species. The in-vitro cytotoxicity of 1, 2 and 3 towards MCF-7 tumor cell lines has been evaluated by MTT method, and show an enhancement of cytotoxicity in UV-A light. The results revealed that complex 1 has superior prospectus to act as cancer chemotherapeutic candidate than that of complex 2 and complex 3.

In the present investigation, a Schiff base N'1,N'3-bis[(E)-(5-bromo-2-hydroxyphenyl)methylidene]benzene-1,3-dicarbohydrazide and its metal complexes have been synthesized and characterized. The DNA-binding studies were performed using absorption spectroscopy, emission spectra, viscosity measurements and thermal denatuaration studies. The experimental evidence indicated that, the Co(II), Ni(II) and Cu(II) complexes interact with calf thymus DNA through intercalation with an intrinsic binding constant Kb of 2.6×10(4) M(-1), 5.7×10(4) M(-1) and 4.5×10(4) M(-1), respectively and they exhibited potent photodamage abilities on pUC19 DNA, through singlet oxygen generation with quantum yields of 0.32, 0.27 and 0.30 respectively. The cytotoxic activity of the complexes resulted that they act as a potent photosensitizers for photochemical reactions.

A new tetra-aza macrocyclic ligand, L (C24H16N12O2S4) and its complexes of type, [MLCl2] and [CuL]Cl2 (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.

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 × 104 M−1 and 2.9 × 104 M−1 and acted as proficient photocleavers of SC pUC19 DNA in UV-A light, forming 1O2 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.