Free radical generation is an inevitable consequence of aerobic existence and is implicated in a wide variety of pathological conditions including cancer, cardiovascular disease, ageing and neurodegenerative disorder. Free radicals can, however, be used to our advantage since their production is catalysed by synthetic inorganic molecules-termed artificial metallonucleases-that cut DNA strands by oxidative cleavage reactions. Here, we report the rational design and DNA binding interactions of a novel di-Cu2+ artificial metallonuclease [Cu-2(tetra-(2-pyridyl)NMe-naphthalene)Cl-4] (Cu-2 TPNap). Cu-2 TPNap is a high-affinity binder of duplex DNA with an apparent binding constant (K-app) of 10(7) M(bp)(-1). The agent binds non-intercalatively in the major groove causing condensation and G-C specific destabilization. Artificial metallonuclease activity occurs in the absence of exogenous reductant, is dependent on superoxide and hydrogen peroxide, and gives rise to single strand DNA breaks. Pre-associative molecular docking studies with the 8-mer d(GGGGCCCC)(2), a model for poly[d(G-C)(2)], identified selective major groove incorporation of the complex with ancillary Cu2+-phosphate backbone binding. Molecular mechanics methods then showed the d(GGGGCCCC)(2) adduct to relax about the complex and this interaction is supported by UV melting experiments where poly[d(G-C)(2)] is selectively destabilized.