Dhar, S.; Nethaji, M.; Chakravarty, A. R. Effect of charge transfer bands on the photo-induced DNA cleavage activity of [1-(2-thiazolylazo)-2-naphtholato]copper(II) complexes.
Journal of Inorganic Biochemistry 2005,
99, 805-812.
Abstract
Ternary copper(II) complex [Cu(TAN)(O2CMe)] (1), where H-TAN is 1-(2-thiazolylazo)-2-naphthol, is prepd. and structurally characterized by X-ray crystallog. The complex has a distorted square pyramidal (4 + 1) CuN2O3 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 DMF. 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, prepd. 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 const. (K app) for 1 is detd. as 9.8 × 105 M-1 from fluorescence quenching expts. using ethidium bromide. The quenching consts. (K) values of 1-3, obtained from the Stern-Volmer plots, are 0.28, 0.52 and 0.49, resp. All the complexes show photo-induced DNA cleavage activity when irradiated with a monochromatic UV light of 365 nm wavelength. A 200 μM complex 1 cleaves ∼75% supercoiled (SC) DNA on 2 h exposure time at 365 nm. A 50 μM soln. of 1 in presence of 100 μM phen and kanamycin-A cleaves ∼99% and ∼60% SC DNA to its nicked circular form, resp., for an exposure of 30 min. The complexes also exhibit significant cleavage of SC DNA on irradn. with visible light of wavelengths 532, 575 and 632.8 nm. Control expts. 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 DMSO and catalase is obsd. 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. [on SciFinder(R)]