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Oxidative cleavage of DNA by a dipyridoquinoxaline copper(II) complex in the presence of ascorbic acid

Santra, Bidyut K. and Reddy, Pattubala AN and Neelakanta, Girish and Mahadevan, Subramony and Nethaji, Munirathinam and Chakravarty, Akhil R (2002) Oxidative cleavage of DNA by a dipyridoquinoxaline copper(II) complex in the presence of ascorbic acid. In: Journal of Inorganic Biochemistry, 89 (3-4). pp. 191-196.

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Complex $[Cu(dpq)_2(H_2O)](ClO_4)_2.H_2O (1)$, where dpq is dipyrido-[3,2-d:2′,3′-f]-quinoxaline, has been prepared by reacting copper(II) perchlorate hexahydrate with dpq in methanol and structurally characterized. The complex crystallizes in the triclinic space group P-1 with the unit cell parameters a=8.646(2) $\AA, b=12.290(5) \AA, c=14.283(4) \AA, α=94.01(2)°, \beta=91.69(2)°,γ=101.60 (3)°, V=1481.7(8) \AA^3$ and Z=2. The structure, refined to R=0.0505 and $R_w=0$.1441 for 5212 reflections with $I>2\sigma$ (I) using 440 parameters, shows the presence of a $CuN_4O$ chromophore in an axially compressed distorted trigonal–bipyramidal structure. The Cu–N distances lie in the range 1.969(3)–2.103(3) $\AA$. The $Cu–OH_2$ distance is 2.145(3) $\AA$. The complex is one-electron paramagnetic and exhibits a visible spectral d–d band at 718 nm in MeCN. It shows a quasi-reversible cyclic voltammetric response at 0.091 V $(ΔE_p=229 mV)$ at 50 $mV s^{−1}$ in MeCN–0.1 M TBAP for the Cu(II)/Cu(I) couple. In 50 mM Tris–HCl/0.1 M KCl buffer–DMF mixture (1:4 v/v, pH 7.2), the couple appears at 0.089 V versus SCE. The complex undergoes facile reduction with sodium ascorbate in an aqueous DMF mixture (4:1 v/v) to form an unstable brown Cu(I) species $(\lambda_max=440 nm$, $\varepsilon=7480 M^{−1} cm^{−1})$ which converts to 1 on exposure to air giving a turnover frequency of ca. 400. Binding studies revealed that 1 is an efficient binder to calf thymus DNA. Complex 1 on reaction with supercoiled (SC) DNA in presence of ascorbic acid in a 50 mM Tris–HCl/50 mM NaCl buffer (pH 7.2) shows nuclease activity which is 4.5 times greater than that of the phen analogue.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Elsevier Science Inc.
Keywords: Copper(II) complex;Nuclease activity;Crystal structure;Redox property
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 01 Feb 2008
Last Modified: 19 Sep 2010 04:41
URI: http://eprints.iisc.ac.in/id/eprint/12622

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