# Effect of charge transfer bands on the photo-induced DNA cleavage activity of [1-(2-thiazolylazo)-2-naphtholato]copper(II) complexes

Dhar, Shanta and Nethaji, Munirathinam and Chakravarty, Akhil R (2005) Effect of charge transfer bands on the photo-induced DNA cleavage activity of [1-(2-thiazolylazo)-2-naphtholato]copper(II) complexes. In: Journal of Inorganic Biochemistry, 99 (3). pp. 805-812.

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## Abstract

Ternary copper(II) complex $[Cu(TAN)(O_2CMe)]$ (1), where H-TAN is 1-(2-thiazolylazo)-2-naphthol, is prepared and structurally characterized by X-ray crystallography. The complex has a distorted square pyramidal (4+1) $CuN_2O_3$ coordination geometry with the acetate showing chelating axial-equatorial binding mode and TAN as a tridentate ligand bonded to the metal in the basal plane. Complex 1 is one-electron paramagnetic and displays ligand-to-metal charge transfer bands at 575 and 398 nm in dimethylformamide. The reactions of 1 with bases (B) like 1,10-phenanthroline (phen) and kanamycin-A (kan-A) afford ternary complexes of formulation $[Cu(TAN)B]^+$ (B=phen, 2; kan-A, 3) under in situ reaction conditions. Complexes 2 and 3, prepared to explore their DNA binding and photo-induced DNA cleavage activity, display good binding propensity to calf thymus (CT) DNA giving a relative order: 2-3>1. The apparent binding constant ($K_a_p_p$) for 1 is determined as $9.8 \times 10^5M^-^1$ from fluorescence quenching experiments using ethidium bromide. The quenching constants (K) values of 1-3, obtained from the Stern-Volmer plots, are 0.28, 0.52 and 0.49, respectively. All the complexes show photo-induced DNA cleavage activity when irradiated with a monochromatic UV light of 365 nm wavelength. A 200 $\mu M$ complex 1 cleaves approximately $\sim75$ % supercoiled (SC) DNA on 2h exposure time at 365 nm. A 50 $\mu M$ solution of 1 in presence of 100 $\mu M$ phen and kanamycin-A cleaves approximately $\sim99$ % and approximately $\sim60$ % SC DNA to its nicked circular form, respectively, for an exposure of 30 min. The complexes also exhibit significant cleavage of SC DNA on irradiation with visible light of wavelengths 532, 575 and 632.8 nm. Control experiments reveal the minor groove binding nature of the complexes. The cleavage reactions involve the formation reactive hydroxyl species as significant inhibition in the presence of dimethyl sulfoxide (DMSO) and catalase is observed. There is no apparent inhibition in cleavage in the presence of singlet oxygen quenchers like sodium azide. The cleavage activity has been found to be higher at the CT band position of 575 nm in comparison to those at 532 and 632.8 nm. The results indicate the involvement of the CT band in the photo-excitation process.

Item Type: Journal Article The Copyright belongs to Elsevier. Copper;DNA photo-cleavage;Crystal structure;Thiazolylazo-2-naphthol; Supramolecular structure Division of Chemical Sciences > Inorganic & Physical Chemistry 27 Feb 2006 19 Sep 2010 04:24 http://eprints.iisc.ernet.in/id/eprint/5679