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Issue 48, 2008
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DNA cleavage in red light promoted by copper(II) complexes of α-amino acids and photoactive phenanthroline bases

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Ternary copper(II) complexes [Cu(L-trp)(B)(H2O)](NO3) (1–3) and [Cu(L-phe)(B)(H2O)](NO3) (4–6) of L-tryptophan (L-trp) and L-phenylalanine (L-phe) having phenanthroline bases (B), viz. 1,10-phenanthroline (phen, 1 and 4), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 2 and 5) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 3 and 6), were prepared and characterized by physico-chemical techniques. Complexes 3 and 6 were structurally characterized by X-ray crystallography and show the presence of a square pyramidal (4 + 1) CuN3O2 coordination geometry in which the N,O-donor amino acid (L-trp or L-phe) and N,N-donor phenanthroline base bind at the equatorial plane with an aqua ligand coordinated at the elongated axial site. Complex 3 shows significant distortion from the square pyramidal geometry and a strong intramolecular π–π stacking interaction between the pendant indole ring of L-trp and the planar dppz aromatic moiety. All the complexes display good binding propensity to the calf thymus DNA giving an order: 3,6 (dppz) > 2,5 (dpq) > 1,4 (phen). The binding constant (Kb) values are in the range of 2.1 × 104–1.1 × 106 mol−1 with the binding site size (s) values of 0.17–0.63. The phen and dpq complexes are minor groove binders while the dppz analogues bind at the DNA major groove. Theoretical DNA docking studies on 2 and 3 show the close proximity of two photosensitizers, viz. the indole moiety of L-trp and the quinoxaline/phenazine of the dpq/dppz bases, to the complementary DNA strands. Complexes 2 and 3 show oxidative DNA double strand breaks (dsb) of supercoiled (SC) DNA forming a significant quantity of linear DNA along with the nicked circular (NC) form on photoexposure to UV-A light of 365 nm and red light of 647.1 nm (Ar–Kr laser). Complexes 1, 5 and 6 show only single strand breaks (ssb) forming NC DNA. The red light induced DNA cleavage involves metal-assisted photosensitization of L-trp and dpq/dppz base resulting in the formation of a reactive singlet oxygen (1O2) species.

Graphical abstract: DNA cleavage in red light promoted by copper(ii) complexes of α-amino acids and photoactive phenanthroline bases

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The article was received on 20 Feb 2008, accepted on 11 Jul 2008 and first published on 21 Oct 2008

Article type: Paper
DOI: 10.1039/B802948B
Citation: Dalton Trans., 2008,0, 6966-6976
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    DNA cleavage in red light promoted by copper(II) complexes of α-amino acids and photoactive phenanthroline bases

    A. K. Patra, T. Bhowmick, S. Ramakumar, M. Nethaji and A. R. Chakravarty, Dalton Trans., 2008, 0, 6966
    DOI: 10.1039/B802948B

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