Oxidative strand scission of nucleic acids by a multinuclear copper(II) complex

Abstract

The compound [Cu₂ ^II(D¹)(H₂O)₂](ClO₄)₄ ^. 2H₂O [D¹=binucleating ligand with tris(2-pyridylmethyl)amine (TMPA) moieties linked in the 5-pyridyl position by a -CH₂CH₂- bridge] mediated efficient oxidative cleavage of pBR322 plasmid DNA under reducing conditions. A mononuclear analogue, [Cu(TMPA)(H₂O)](ClO₄)₂, was less effective at linearizing supercoiled (Form I) plasmid DNA as compared to the binuclear complex. A new method for quenching the copper-dependent reactions has been developed to avoid plasmid scission by the binuclear complex and the standard gel loading buffer. EDTA was not sufficient for retarding copper reaction, but diethyldithiocarbamic acid was capable of inhibiting all reactivity. Investigation of oxidative cleavage of double-helical oligonucleotides by [Cu₂ ^II(D¹)(H₂O)₂](ClO₄)₄ confirmed the enhanced reactivity of the binuclear over the mononuclear complex and provided mechanistic insights into the nature of the reaction. Cleavage of DNA required both the binuclear complex and a reductant and likely proceeded through an O₂-derived intermediate that does not include a diffusible hydroxyl radical. The greater efficiency of the binuclear complex relative to the mononuclear analogue is consistent with their relative abilities to activate dioxygen. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00775-002-0369-8.