Towards mismatched DNA photoprobes and photoreagents: “elbow-shaped” Ru(ii) complexes†
Due to their potentially harmful consequences, the detection of mismatched DNA is a subject of high interest. In order to probe DNA mismatches by means of luminescent sensitive Ru(II) complexes, “elbow-shaped” extended planar ligands based on an acridine or phenazine core have been synthesized (npp = naphtho[1,2-b]pyrido[3,2-f][1,7]phenanthroline and bdppz = benzo[h]dipyrido[3,2-a:2′,3′-c]phenazine). The photophysical studies revealed that [Ru(bpy)2npp]2+ (bpy = 2,2′-bipyridine) allows emission from a 3MLCTbpy/npp excited state, while the lowest 3MLCT for [Ru(bpy)2bdppz]2+ shifts from a bright 3MLCTbpy/pz state towards a poorly luminescent 3MLCTbdp state, probably due to the formation of H-bonds with water molecules in the excited state. Studies of the complexes in the presence of DNA demonstrate that they strongly bind to polynucleotides. In the presence of single base mismatched hairpin oligonucleotides, while [Ru(bpy)2npp]2+ does not show remarkable sensitivity to the nature of the mismatch site, [Ru(bpy)2bdppz]2+ exhibits noticeably differential luminescence behavior correlated to the nature and stability of the mismatch compared to the well-matched sequence. Photooxidant analogues of these complexes were prepared, replacing bpy ancillary ligands by bpz (2,2′-bipyrazine). A photo-induced electron transfer from dGMP and polynucleotides to the excited states of [Ru(bpz)2npp]2+ and [Ru(bpz)2bdppz]2+ is observed. These results emphasized the role of “elbow-shaped” Ru(II) complexes as promising candidates for the development of mismatch-sensitive DNA photoprobes.