Metal-assisted light-induced DNA cleavage activity of 2-(methylthio)phenylsalicylaldimine Schiff base copper(II) complexes having planar heterocyclic bases

Reddy, Pattubala AN and Santra, Bidyut K and Nethaji, Munirathinam and Chakravarty, Akhil R (2004) Metal-assisted light-induced DNA cleavage activity of 2-(methylthio)phenylsalicylaldimine Schiff base copper(II) complexes having planar heterocyclic bases. In: Journal of Inorganic Biochemistry, 98 (2). pp. 377-386.

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Abstract

Ternary copper(II) complexes [CuLL']$(ClO_4)$, where HL is NSO-donor Schiff base (2-(methylthio)phenyl)salicylaldimine and L' is NN-donor phenanthroline bases like 1,10-phenanthroline (phen), dipyridoquinoxaline (dpq) and 2,9-dimethyl-1,10-phenanthroline (dmp), are prepared and structurally characterized by X-ray crystallography. The complexes have a distorted square-pyramidal (4+ 1) $CuN_3OS$ coordination geometry. While $[CuL(phen)](ClO_4)$ and $[CuL(dpq)](ClO_4)$ show axial sulfur ligation, $[CuL(dmp)](ClO_4)$ has the sulfur bonded at the equatorial site. The one-electron paramagnetic complexes exhibit axial electron paramagnetic resonance (EPR) spectra in dimethylformamide glass at 77 K. The complexes are redox active and a quasireversible electron transfer process near 0.0 V vs saturated calomel electrode (SCE) in DMF–Tris buffer (1:4 v/v at pH 7.2) involving Cu(II)/ Cu(I) couple is observed for the phen and dpq complexes. The dmp complex exhibits an irreversible reduction proces forming bis(dmp)copper(I) species. A profound effect of the substituents of the phenanthroline bases is observed on the binding of the complexes to the calf thymus (CT) and in the cleavage of supercoiled (SC) pUC19 DNA. The phen and dpq complexes show DNA cleavage activity in presence of mercaptopropionic acid (MPA). The dmp complex is cleavage inactive in presence of MPA. All the complexes show photocleavage activity when irradiated with a monochromatic UV light of 312 nm. The dpq complex also cleaves SC DNA on visible light irradiation at 436, 532 and 632.8 nm but with a longer exposure time and higher complex concentration. The cleavage reactions in presence of MPA are found to involve hydroxyl radical. The photocleavage reactions are found to occur under aerobic conditions showing an enhancement of cleavage in $D_2O$ and inhibition with azide addition suggesting formation of singlet oxygen as a reactive species The roles of sulfur of the Schiff base as photosensitizer and the phenanthroline bases as minor groove binder, and their influence on the photocleavage activity are discussed. The quinoxaline ligand exhibits significant photosensitizing effect assisted by the copper(II) center.

Item Type:	Journal Article
Publication:	Journal of Inorganic Biochemistry
Publisher:	Elsevier
Additional Information:	The copyright belongs to Elsevier.
Keywords:	Copper;DNA photocleavage;Schiff base;Crystal structure;Phenanthroline bases
Department/Centre:	Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited:	31 May 2006
Last Modified:	19 Sep 2010 04:28
URI:	http://eprints.iisc.ac.in/id/eprint/7149

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