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New insights into the visible-light-induced DNA cleavage activity of dipyridoquinoxaline complexes of bivalent 3d-metal ions

Roy, Mithun and Pathak, Biswarup and Patra, Ashis K and Jemmis, Eluvathingal D and Nethaji, Munirathinam and Chakravarty, Akhil R (2007) New insights into the visible-light-induced DNA cleavage activity of dipyridoquinoxaline complexes of bivalent 3d-metal ions. In: Inorganic Chemistry, 46 (26). pp. 11122-11132.

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Dipyridoquinoxaline (dpq) complexes of bivalent 3d-metal ions, viz., $[Fe^{II}(dpq)_3](PF_6)_2 (1), [Co^{II}(dpq)_3](ClO_4)_2 (2)$, $[Ni^{II}(dpq)_3](ClO_4)_2 (3)$, $[Cu^{II}(dpq)_2(H_2O)](ClO_4)_2 (4)$, $[Zn^{II}(dpq)_3](ClO_4)_2 (5)$, and $[Zn^{II}(dpq)_2(DMF)_2](ClO_4)_2 (5a)$ (DMF = N,N-dimethylformamide), are prepared and their photoinduced DNA cleavage activity studied. Structural characterization for the complexes 1 and 5a is done by single-crystal X-ray crystallography. All the complexes show efficient binding propensity to calf thymus DNA with a binding constant (K) value of $\sim 10^5 M^{-1}$. Complexes 1, 2, and 4 show metal-based cyclic voltammetric responses at 1.2, 0.4, and 0.09 V (vs SCE) in DMF 0.1 M $[Bu^n_4N](ClO_4)$ assignable to the respective $Fe^{III}/Fe^{II}, Co^{III}/Co^{II}$, and $Cu^{II}/Cu^{I}$ couples. The $Ni^{II}$ and $Zn^{II}$ complexes do not show any metal-based redox process. The dpq-based reductions are observed in the potential range of -1.0 to -1.7 V vs SCE. DNA melting and viscosity data indicate the groove-binding nature of the complexes. Control experiments using distamycin-A suggest a minor groove-binding propensity of the complexes. The complexes exhibit photoinduced cleavage of supercoiled pUC19 DNA in UV light of 365 nm. The diamagnetic $d^6-Fe^{II}$ and $d^{10}-Zn^{II}$ complexes are cleavage-inactive on irradiation with visible light. The paramagnetic $d^7-Co^{II}$ and $d^9-Cu^{II}$ complexes exhibit efficient DNA cleavage activity on photoirradiation at their respective d-d band. The paramagnetic $d^8-Ni^{II}$ complex displays only minor DNA cleavage activity on irradiation at its d-d band. The DNA cleavage reactions at visible light under aerobic conditions involve the formation of hydroxyl radical. The $Co^{II}$ complex shows photocleavage of DNA under an argon atmosphere. Theoretical calculations on the complexes suggest a photoredox pathway in preference to a type-2 process forming singlet oxygen for the visible-light-induced DNA cleavage activity of the 3d-metal complexes. The theoretical data also predict that the photoredox pathway is favorable for the $3d^7-Co^{II}$ and $3d^9-Cu^{II}$ complexes to exhibit DNA cleavage activity, while the analogous $3d^6-Fe^{II}$ and $3d^8-Ni^{II}$ complexes are energetically unfavorable for the exhibition of such activity under visible light. The CoII and CuII complexes are better suited for designing and developing new metal-based PDT agents than their cleavage-inactive $Fe^{II}, Ni^{II}$, and $Zn^{II}$ analogues.

Item Type: Journal Article
Publication: Inorganic Chemistry
Publisher: American Chemical Society
Additional Information: Copyright of this article belongs to American Chemical Society.
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 13 Feb 2008
Last Modified: 19 Sep 2010 04:42
URI: http://eprints.iisc.ac.in/id/eprint/13036

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